Non-technical Summary
Turritelline-dominated assemblages (TDAs) are globally very common and appear in marine sedimentary successions from the Late Jurassic onward. This study describes a diverse TDA from the early Miocene of Dwarka Basin, western India. The TDA shows a remarkable diversity of 42 gastropod species, four of which are new. The turritelline gastropods also show a notable diversity of eight species assigned to two genera. Petrographic studies and associations of foraminifera such as Lockhartia sp., Miogypsina sp., Operculina sp., Ammonia sp., and so on suggest a shallow-marine subtidal–intertidal, tropical, warm, nutrient-rich, and well-oxygenated paleoenvironment during the deposition of the TDA bed.
Introduction
Turritelline gastropods (family Turritellidae Lovén, Reference Lovén1847) are one of the most frequent faunal elements of benthic marine assemblages from the Late Jurassic to the present times (Allmon and Harris, Reference Allmon and Harris2008; Das et al., Reference Das, Saha, Bardhan, Mallick and Allmon2018). These gastropods often dominate the faunal composition, sometimes being the sole macrofaunal component, forming a turritelline-dominated assemblage (TDA; sensu Allmon, Reference Allmon2007). TTDAs are assemblages in which the turritelline gastropods either: (1) constitute at least 20% of the entire biomass, or (2) are at least two or three times more abundant than other macrofauna within the assemblage (Allmon and Knight, Reference Allmon and Knight1993; Allmon, Reference Allmon2007; Allmon and Cohen, Reference Allmon and Cohen2008; Allmon and Harris, Reference Allmon and Harris2008).
TDAs are globally very common and appear in both siliciclastic and carbonate sedimentary successions through the ages (see Allmon and Knight, Reference Allmon and Knight1993). Over the past few decades, significant studies have focused on their diversity, ecology, and taphonomic characteristics (Allmon and Knight, Reference Allmon and Knight1993; Allmon and Cohen, Reference Allmon and Cohen2008; Allmon and Harris, Reference Allmon and Harris2008; Anderson et al., Reference Anderson, Hendy, Johnson and Allmon2017; Nebelsick et al., Reference Nebelsick, Rasser, Höltke, Thompson and Bieg2020, and many more). In the Indian subcontinent, extensive studies on TDAs have been conducted mainly from the Late Jurassic of western India (Kutch Basin) (Das et al., Reference Das, Saha, Bardhan, Mallick and Allmon2018, Reference Das, Mondal, Saha, Bardhan and Saha2019, Reference Das, Saha, Bardhan, Mondal, Paul, Mallick, Saha and Allmon2024; Bardhan et al., Reference Bardhan, Saha, Das and Saha2021), the Late Cretaceous of southern India (Rajahmundry Basin) (see Mallick et al., Reference Mallick, Bardhan, Paul, Mukherjee and Das2013, Reference Mallick, Bardhan, Das, Paul and Goswami2014) and central India (Narmada Basin) (see Mondal et al., Reference Mondal, Das, Bhattacharya and Halder2024), and the early Miocene of western India (Kutch Basin) (see Goswami et al., Reference Goswami, Das, Bardhan and Paul2021). However, no such studies have been conducted in the Dwarka Basin of western India, which contains a vast record of Cenozoic marine mollusks (Jain, Reference Jain2014).
Jain (Reference Jain2014) first mentioned the presence of a “turritella” bed in the area north of Bhatiya Village of Devbhumi Dwarka District of Gujarat, India. This bed is stratigraphically classified into the Nandana Member of the Gaj Formation (Burdigalian, early Miocene). However, Jain (Reference Jain2014) did not undertake a detailed study on this bed. In the present study, extensive sampling has been done on this bed to shed further light on its gastropod diversity.
Our collection from this bed revealed a high diversity of micro-mollusks alongside the turritelline gastropods, prompting a systematic study on these smaller species. Micro-mollusks are a major component of marine and terrestrial molluscan communities, characterized by their extremely small size even in their adulthood (size range generally less than 5 mm) (Geiger et al., Reference Geiger, Marshall, Ponder, Sasaki and Waren2007). Due to their minute size, these tiny mollusks are often overlooked and are among the most understudied marine faunal elements (for some notable studies on Indo–western Pacific modern micro-mollusks, see Sasaki, Reference Sasaki2008; Zuschin et al., Reference Zuschin, Janssen and Baal2009; Janssen et al., Reference Janssen, Zuschin and Baal2011). A recent study by Banerjee and Halder (Reference Banerjee and Halder2024) also recorded several micro-mollusks from the Ypresian (early Eocene) succession of the Cambay Basin, western India. The Miocene marine sequences, in particular, are terra-incognita for these tiny molluscan faunas. Only two notable studies exist on seagrass-associated micro-gastropod assemblages of the early Miocene (Burdigalian) of Quilon, southern India (Harzhauser, Reference Harzhauser2014), and Banyunganti, south-central Java, Indonesia (Reich et al., Reference Reich, Wesselingh and Renema2014). In the present study, we describe a considerable number of Miocene micro-gastropod species found in the studied gastropod assemblage and briefly discuss the depositional environment of the TDA bed.
Geological settings and stratigraphy
The specimens examined in this study were collected from three fossil localities within the Nandana Shale–Siltstone Unit (Nmb Unit) of the Nandana Member, Gaj Formation of the Dwarka Basin, western India (see Fig. 1). The Dwarka Basin is a peri-cratonic shelf basin situated on the western margin of the Kathiawar Peninsula, featuring an extensive succession of Neogene marine sediments (Jain, Reference Jain2014; Bose et al., Reference Bose, Das and Saha2023). The stratigraphic succession is divided into three formations—in ascending order, they are the Gaj, Dwarka, and Miliolite Limestone formations—which collectively span from the early Miocene (Burdigalian) to the Holocene. This succession unconformably overlies the Deccan Traps and associated laterite (Jain, Reference Jain2014; Bose et al., Reference Bose, Das and Saha2023).
Figure 1. Geographic location of the Devbhumi Dwarka District of Gujarat, India, shown in the upper panel; lower panel shows fossil-bearing localities in the Dwarka Basin.
The Gaj Formation (early Miocene–middle Miocene) is further subdivided into seven lithostratigraphic members: Nandana Member, Kuranga Member, Ranjitpur Member, Ashapuramata Member, Charkala Member, Lowrali Member, and Dabla Mandir Member (Fig. 2; Jain, Reference Jain2014; Bose et al., Reference Bose, Das and Saha2023). Among these, the Nandana Member forms an ~10 m thick succession that unconformably overlies the Deccan Traps, laterites, and weathered trap derivatives. This member is extensively exposed around the villages of Pindara, Mahadeviya, Nandana, Bhatiya, and Hadmatiya in Gujarat, India (Bose et al., Reference Bose, Das and Saha2023).
Figure 2. Lithostratigraphic table of the Cenozoic succession of the Dwarka Basin (after Jain, Reference Jain2014) along with a composite litholog showing four different units (Nma, Nmb, Nmc, and Nmd) of the Nandana Member of the Gaj Formation. w = wackestone; p = packstone; g = grainstone; b = boundstone; f = fine; m = medium; c = coarse. For different unit abbreviations, see Geology section.
The Nandana Member is further subdivided into four lithounits—in ascending stratigraphic order, these are: (1) Basal Nandana Limestone Unit (Nma), composed of highly fossiliferous packstone containing abundant fossils of bivalves, gastropods, corals, echinoids, and crabs (Bose et al., Reference Bose, Das and Saha2023); (2) Nandana Shale–Siltstone Unit (Nmb) (Figs. 2, 3), characterized by highly fossiliferous brown shale interbedded with a thin (~20 cm) fossiliferous siltstone layer, consistently hosting a TDA along with bivalves, echinoids, and crabs (Bose et al., Reference Bose, Das and Saha2023); (3) Nandana Sandstone Unit (Nmc), characterized by medium-grained shell-hash beds and medium-grained sandstone (Bose et al., Reference Bose, Das and Saha2023); and (4) upper Nandana Limestone Unit (Nmd), composed of sparsely fossiliferous wackestone, strongly bioturbated at the base with large burrow infills and karstic top surfaces. Fossils include corals and mollusks (oysters and gastropods) (Bose et al., Reference Bose, Das and Saha2023).
Figure 3. Field photographs showing two different litho-sections of the Nandana Member of the Gaj Formation, Dwarka Basin. The left photograph shows a litho-section 3 km northwest of Bhatiya Village showing Nma, Nmb, and Nmc units. The right and bottom photographs are from a litho-section 2.7 km north-northeast of Gokalpar Village showing Nmb and Nmc units. The bottom photograph shows abundant turritelline gastropods lying around. The hammer represents the scale, with length 34 cm.
Materials and methods
The gastropod specimens were collected from three different fossil-bearing localities within the Nandana Shale–Siltstone Unit (Nmb) of the Gaj Formation in the Dwarka Basin, Gujarat, India. These localities are identified as Loc. 1 (Nmb1), Loc. 2 (Nmb2), and Loc. 3 (Nmb3). Loc. 1 (Nmb1) is situated 2.7 km north-northeast of Gokalpar Village and 2.2 km south of Bhatiya Village, Devbhoomi Dwarka District (22°04ʹ01.0"N, 69°16ʹ07.9"E). Loc. 2 (Nmb2) is located 2.4 km northwest of Bhatiya Village (22°06ʹ13.0"N, 69°15ʹ11.2"E), and Loc. 3 (Nmb3) is located at a laterite quarry, 770 m northwest of Pindara Village (22°14ʹ55.9"N, 69°14ʹ59.1"E) (Fig. 1).
Three bulk collections were made from these localities: Bulk 1 and Bulk 2, each from a 3 m × 3 m grid at Loc. 1, and Bulk 3 from a 1 m × 1 m grid at Loc. 2, where exposures were substantially scattered. The specimens were collected in random from Loc. 3 since the exposure was not suitable for bulk collection. These collections yielded a total sample size of 7,323 gastropod specimens. In the laboratory, the specimens were separated from the bulk samples using sieves of varying mesh sizes (ASTM 12: 1.70 mm; ASTM 14: 1.40 mm; ASTM 18: 1.00 mm). The specimens were then identified at the supraspecific and species levels, following the morphological criteria and terms established in previous literature (e.g., Vredenburg, Reference Vredenburg1925, Reference Vredenburg1928; Harzhauser et al., Reference Harzhauser, Reuter, Piller, Berning, Kroh and Mandic2009; Kulkarni et al., Reference Kulkarni, Kapoor and Borkar2010; Jain, Reference Jain2014). The classification of Bouchet et al. (Reference Bouchet, Rocroi, Hausdorf, Kaim, Kano, Nützel, Parkhaev, Schrödl and Strong2017) is followed for systematic arrangement of the gastropods.
For detailed study, macro-specimens were examined under a stereo microscope (Olympus SZX16, IISER, Kolkata) while micro-specimens were photographed using a Leica DVM6 microscope (ISI, Kolkata) and a scanning electron microscope (Jeol JSM 6490, IIT Kharagpur). The protoconchs of the turritelline specimens were studied and photographed using a scanning electron microscope, (JEOL JSM-IT800, IIT Bombay) (Supplementary Figs. 2–6). The apical sculpture formula of the turritelline species were assessed following Allmon (Reference Allmon1996).
The taxonomic diversity of the gastropods was systematically tabulated and visualized through simple pie charts and bar plots at the family, genus, and species levels (Fig. 4; Table 1). The adequacy of the specimen collection and species richness was evaluated by generating a rarefaction curve using PAST software (Supplementary Fig. 1). To further explore the ecological diversity, a three-dimensional ecological morphospace was constructed using the Bambachian Cube concept (Mondal and Harries, Reference Mondal and Harries2016). This morphospace utilized three axes representing different life habit traits: Axis 1 (tiering) categorized specimens into benthic epifaunal (EP) and benthic semi-infaunal (SI); Axis 2 (motility) classified them as actively mobile (AM), facultatively mobile (FM), slow moving (SM), or stationary (S); and Axis 3 (diet) included categories such as predatory carnivores (CP), browsing carnivores (CB), omnivores–grazers (HO), herbivores–grazers (HG), suspension feeders (SU), and scavengers–predators (SP). Data on the life habits of these gastropods were sourced from the Paleobiology Database (www.paleobiodb.org/), WoRMS (https://www.marinespecies.org/), and Neogene Marine Biota of Tropical America (https://nmita.rsmas.miami.edu/). The Bambachian cubes are based on the abundance of gastropods (number of specimens) and are grouped into nine different classes: ≤5, 6–15, 16–25, 26–35, 36–45, 46–55, 56–65, 66–75, >75 (Fig. 5).
Figure 4. Gastropod diversity of the Nandana Shale–Siltstone Unit (Nmb) (Nandana Member). (1) Pie diagram showing family-level gastropod diversity of the Nmb unit. (2) Pie diagram showing gastropod diversity of other associated families of the Nmb unit. (3) Pie diagram showing genus-level gastropod diversity of the Nmb unit. (4) Pie diagram showing gastropod diversity of other associated genera of the Nmb unit. (5) Bar plot showing species-level diversity of turritelline gastropods in three different localities of Nmb (Nmb1, Nmb2, and Nmb3). (6) Bar plot showing diversity of associated gastropod species (N > 10) in three different localities of the Nmb unit (Nmb1, Nmb2, and Nmb3).
Table 1. List of all gastropod species, their specimen counts, and ecology (tier, mobility, and diet) in different fossil localities of the Nandana Shale-Siltstone Unit (Nmb), Gaj Formation, Dwarka Basin (for abbreviations, see the Materials and methods section)
Figure 5. Three-dimensional Bambachian cube with the three axes showing tier, motility, and diet to visualize the temporal variations in ecological diversity of the Nandana Shale–Siltstone Unit (Nmb) of the Gaj Formation, Dwarka Basin. The models are plotted according to abundance of species of the unit. EP = benthic epifaunal; SI = benthic semi-infaunal; AM = actively mobile; FM = facultatively mobile; SM = slow moving; S = stationary; CP = predatory carnivores; CB = browsing carnivores; HO = omnivores–grazers; HG = herbivores–grazers; SU = suspension feeders; SP = scavengers–predators.
In addition, thin-section petrography and microfossil identification were conducted and photographed using the Leica DM 4P (ISI, Kolkata) and Zeiss Axio Imager M2m (IIT (ISM) Dhanbad) microscopes (Figs. 6, 7).
Figure 6. Petrographic thin-section images showing different identified microfossils and microfacies of the shale bed of the Nandana Shale–Siltstone Unit (Nmb) of Nandana Member, Gaj Formation, Dwarka Basin, western India. (1) Presence of angular quartz grains (Q) in clay-rich matrix showing undulose extinction (XPL image). (2) Halimeda sp. (PPL image). (3) Miogypsina sp. (PPL image). (4) Ammonia sp. (PPL image). (5) Miliolid foraminifera (PPL image). (6) Operculina sp. (PPL image). (7) Quinqueloculina sp. (PPL image). PPL= plane polarized light; XPL = crossed polarized light. (1) Scale bar = 100 μm; (2, 4, 5) scale bars = 200 μm; (3, 6, 7) scale bars = 1 mm.
Figure 7. Petrographic thin-section images showing different identified microfossils and microfacies of the siltstone bed of the Nandana Shale–Siltstone Unit (Nmb) of Nandana Member, Gaj Formation, Dwarka Basin, western India. (1) Monocrystalline quartz crystals with angular grain boundary (XPL image). (2) Rotalid foraminifera (PPL image). (3) Ammonia sp. (PPL image). (4) Well-preserved barnacle showing the array of pores (PPL image). (5) Plagioclase feldspar grains showing laminar twinning and muscovite grains are prominent within this section (XPL image). PPL= plane polarized light; XPL= crossed polarized light. (1–3) Scale bars = 100 μm; (4) scale bar = 500 μm; (5) scale bar = 250 μm.
Repository and institutional abbreviation
All specimens are archived in the Museum of Geological Studies Unit, Indian Statistical Institute, Kolkata, India. Specimens are numbered following the institutional abbreviation: ISI/dwk/TDA and ISI/dwk/TDAG. ISI = Indian Statistical Institute; dwk = Dwarka; TDA = turritelline-dominated assemblage; TDAG = TDA gastropods.
Systematic paleontology
Class Gastropoda Cuvier, Reference Cuvier1797
Subclass Vetigastropoda Salvini-Plawen, Reference Salvini-Plawen1980
Order Lepetellida Moskalev, Reference Moskalev1971
Superfamily Fissurelloidea Fleming, Reference Fleming1822
Family Fissurellidae Fleming, Reference Fleming1822
Subfamily Emarginulinae Children, Reference Children and Children1834
Genus Emarginula Lamarck, Reference Lamarck1801
Type species
Emarginula conica Lamarck, Reference Lamarck1801 (type by monotypy); European seas, Recent.
Emarginula sp.
Figure 8. Emarginula sp., specimen number ISI/dwk/TDAG/15/i: (1) apical view; (2) right lateral view; (3) left lateral view; (4) view of the apex; (5) basal view. Scales bars = 500 μm.
Materials
One poorly preserved specimen (ISI/dwk/TDAG/15/i). ISI/dwk/TDAG/15/i has shell preserved with ornamentation partly discernible. The specimen is collected from the Bulk 1 of the Nandana Shale–Siltstone Unit (NMb) of Loc. 1 (Fig. 1).
Occurrence
Early Miocene (Burdigalian), Dwarka Basin, Gujarat, India.
Description
Moderately thick shell, medium sized for the family, relatively low in height, patelliform with shell height 2.98 mm, shell width 3.62 mm, and shell length 5.15 mm. Basal plane is flat, and basal outline is an elongated oval (long axis anteroposteriorly oriented with the anterior and posterior sides equally rounded), margin slightly crenulated. Apex is strongly recurved but does not overhang the posterior edge. The rounded boss at the apex is placed nearly at the posterior margin of the shell. Protoconch is indiscernible, but the earlier whorls are clearly tilted to the left. Anterior margin of the shell along with part of the slit boundary is slightly broken. Slit is narrow and very short in length. Ornamentation of the selinizone is indiscernible. The shell surface is ornamented by 12 closely spaced axial ribs with a single secondary rib intercalated in the interspaces. Ribs crossed by very weak, nearly inconspicuous concentric lamellas.
Remarks
Emarginula sp. shares similarities with Emarginula adriatica Costa, Reference Costa1830, reported from the upper Miocene of northwestern France, particularly in terms of overall shell shape and size (see Landau et al., Reference Landau, Van Dingenen and Ceulemans2017, p. 83, plate 6, figs. 1, 2). However, notable differences exist in shell surface ornamentation between the two species. E. adriatica features strong axial sculpture with papillae formed at the intersections of the axial ribs and equally strong concentric ribs. By contrast, Emarginula sp. exhibits shell ornamentation consisting of closely spaced axial ribs crossed by very weak concentric lamellas.
Emarginula sp. differs significantly from Emarginula subclatharata Pilsbry, Reference Pilsbry1890 (see Pilsbry, Reference Pilsbry1890, p. 266–267, plate 28, fig. 27; currently accepted as Emarginula dilecta Adams, Reference Adams1852 in WoRMS) in both ornamentation and the length of the anal slit. While Emarginula sp. has a short and narrow slit and 12 closely spaced axial ribs, E. subclatharata possesses a long, elongated anal slit and 22 prominent radial ribs. However, due to the limited number of preserved specimens and absence of definitive diagnostic features, assignment to a new species was not possible.
Order Trochida (Cox and Knight, Reference Cox and Knight1960)
Superfamily Trochoidea Rafinesque, Reference Rafinesque1815
Family Trochidae Rafinesque, Reference Rafinesque1815
Subfamily Cantharidinae Gray, Reference Gray1857
Genus Clelandella Winckworth, Reference Winckworth1932
Type species
Clelandella miliaris Brocchi, Reference Brocchi1814 (by original description); Mediterranean Sea, Pliocene.
?Clelandella saurashtraensis new species
Figure 9. ?Clelandella saurashtraensis n. sp. (1, 2) Specimen number ISI/dwk/TDAG/33/ii (paratype): (1) abapertural view; (2) apertural view. (3–5) Specimen number ISI/dwk/TDAG/33/i (holotype): (3) abapertural view; (4) apertural view; (5) apical view. (6–8) Specimen number ISI/dwk/TDAG/33/iii (paratype): (6) abapertural view; (7) apertural view; (8) close-up view of the early teleoconch whorls with the red triangles showing three fine weakly beaded spirals. Scale bars = 500 μm.
Holotype
Specimen number ISI/dwk/TDAG/33i. Nandana Shale–Siltstone Unit, Nandana Member, Gaj Formation, Dwarka Basin, India; early Miocene (Burdigalian).
Materials
Four well-preserved specimens (ISI/dwk/TDAG/33 i–iv). The specimens are collected from Bulk 1 of Loc. 1 (Fig. 1).
Diagnosis
The early teleoconch whorl ornamented by three fine weakly beaded spiral laminae, the later whorls ornamented by regularly spaced four spiral ribs; anomphalous with axis covered by columellar lip.
Occurrence
Early Miocene (Burdigalian), Dwarka Basin, Gujarat, India.
Description
Small-sized trochiform shell, higher than broad (height [H] = 3.39 mm, diameter [D] = 2.94 mm). The overall shell shape is slightly cyrtoconic with apical angle 63°–64° and pleural angle 65°–67°. Protoconch consists of only one smooth convex whorl. Teleoconch with up to three or four convex whorls. Suture is impressed. The early teleoconch is ornamented by three very fine, nearly smooth to weakly beaded spiral laminae, which are gradually strengthened in the latter teleoconch whorls. The later whorls are ornamented by four regularly spaced spiral ribs. Fine regularly spaced prosocline axial lirae can be observed crosscutting the spiral ribs, resulting in a beaded appearance. The peripheral margin of the last whorl is demarcated by a sharp keel-like beaded spiral angulation. Base is weakly convex and ornamented by five spiral ribs, weakly beaded in appearance. Shell is anomphalous, and the axis is covered by a columellar lip. Subcircular aperture, strongly prosocline, present at the basal part of the shell.
Etymology
Named after Saurashtra (Kathiawar) Peninsula of India.
Remarks
The specimens are characterized by conical shell that is higher than broad, and the spire is sculptured with beaded spiral threads, which is very similar to Calliostoma Swainson, Reference Swainson1840. However, the protoconch consists of one smooth whorl in contrast to Calliostoma, which has a honeycomb pattern in the protoconch (Hickman and McLean, Reference Hickman and McLean1990). The characteristic smooth protoconch, similar shell size and morphology, along with similar shell surface ornamentation, are found in the genus Clelandella Winckworth, Reference Winckworth1932. Clelandella has all the modern species recorded from the eastern Atlantic coasts and the Mediterranean Sea (Gofas, Reference Gofas2005; WoRMS, 2025). In the Indo–western Pacific Region, the genus records the only species from the Burdigalian strata of the Quilon, Kerala, Indian subcontinent— Clelandella sovisi Harzhauser, Reference Harzhauser2014 (see Harzhauser Reference Harzhauser2014, p. 84, pl. 2, figs. 14–16)—although the generic assignment remains dubious. Our specimens are highly comparable to Clelandella sovisi in many morphological respects such as shell size, protoconch, periphery of the last whorl having a sharp keel-like angulation, and aperture. In addition, they occur in two basins very close biogeographically. Thus, the specimens are tentatively assigned to the genus Clelandella. C. sovisi has a deep, small, semi-lunar-shaped umbilicus whereas ?Clelandella saurahtraensis n. sp. is anomphalous. In addition, the shell surface ornamentation of C. sovisi in the later whorls shows smooth spiral ribs that range from six to eight in number. By contrast, C. saurasthraensis consistently displays four regularly spaced beaded spiral ribs.
?Clelandella saurahtraensis differs from the recent species from the Atlantic Ocean and Mediterranean, Clelandella miliaris (Brocchi, Reference Brocchi1814), in number of teleoconch whorls and shell surface sculpture (Gofas, Reference Gofas2005, p. 134, figs. 1–3). Clelandella miliaris is characterized by seven to eight teleoconch whorls and whorls ornamented by beaded spiral cords with a prominent beaded rim running beneath the suture.
?Clelandella saurahtraensis differs from another recent Mediterranean species, Clelandella dautzenbergi Gofas, Reference Gofas2005 (Gofas, Reference Gofas2005; p. 136, figs. 4, 5), mainly in terms of number of whorls, whorl profile, suture, and shell surface ornamentation. C. dautzenbergi has seven to eight teleoconch whorls characterized by convex earlier teleoconch whorls while the later whorls are nearly flat to swollen subsuturally in profile. Suture is canaliculate with the later whorls showing five to eight additional spiral cords.
Genus Jujubinus di Monterosato, Reference di Monterosato1884
Type species
Trochus matonii Payraudeau, Reference Payraudeau1826 (= Jujubinus exasperatus (Pennant, Reference Pennant1777)) (by subsequent designation, Crosse, Reference Crosse1885, p. 140), Recent, Mediterranean.
Jujubinus dwarkaensis new species
Figure 10. (1, 2) Jujubinus dwarkaensis n. sp., specimen number ISI/dwk/TDAG/37/i (holotype): (1) apertural view; (2) abapertural view. (3–5) Gibbula sp., specimen number ISI/dwk/TDAG/38/i: (3) abapertural view; (4) apertural view; (5) apical view. (6, 7) Neocollonia aff. N. pseudomunda (Harzhauser, Reference Harzhauser2014), specimen number ISI/dwk/TDAG/34/i: (6) broken abapertural view; (7) apical view. (1, 2) Scale bars = 1 mm; (3–7) scale bars = 500 μm.
Holotype
Specimen number ISI/dwk/TDAG/37/i. Nandana Shale–Siltstone Unit, Nandana Member, Gaj Formation, Dwarka Basin, India; early Miocene (Burdigalian).
Materials
One well-preserved specimen (ISI/dwk/TDAG/37/i). The specimen was collected from Bulk 2 of Loc. 1 (Fig. 1).
Diagnosis
Whorls bear opisthocline axial ribs crossed by weak spiral threads forming small tubercles at their intersection, weakly curved base.
Occurrence
Early Miocene (Burdigalian), Dwarka Basin, Gujarat, India.
Description
Shell is small, trochiform, cyrtoconic, with a high spire (H = 4.89 mm, D = 2.52 mm) and weakly convex base. Protoconch is not preserved. Six teleoconch whorls with nearly straight-sided to convex whorls throughout the ontogeny. Apical angle is 41°, and pleural angle is 43°. Suture is narrow, linear, and impressed. The teleoconch whorls bear regularly spaced opisthocline axial ribs as ornamentation, which get strengthened in the latter whorls. The axial ribs are crosscut by two (in earlier whorls) to three (in the latter whorls) weak spiral threads, resulting in a beaded appearance of the axial ribs with small tubercles formed at their intersection. The periphery of the last whorl is marked by a prominent spiral thread that separates the last whorl from the weakly convex base. Umbilicus is not visible, with ornamentation of the base indiscernible. Aperture is subquadrate in shape with the outer lip slightly convex while the columellar lip is straight. Base of the aperture is slightly curved.
Etymology
Named after the city of Dwarka, Gujarat, India.
Remarks
Although the overall shape of Jujubinus dwarkaensis is reminiscent of the Burdigalian species Jujubinus keralaensis Harzhauser, Reference Harzhauser2014 from Quilon, southern India (see Harzhauser, Reference Harzhauser2014, p. 85, plate 2, figs. 10–13), the shell surface ornamentation of these two species differs considerably. J. keralaensis is characterized by sculpture of spiral ribs on the teleoconch whorls and possesses an open, semi-lunar umbilicus. By contrast, J. dwarkaensis features dominant axial ribs crossed by fine spiral threads as its shell surface ornamentation, and it lacks an umbilicus.
Persistent strong axial ribs are rare in Jujubinus. Jujubinus subturgidulus (d’Orbigny, Reference d’Orbigny1852), an early Miocene (Aquitanian) species from France, has a shell characterized by oblique axial sculpture between strong spiral ribs (Lozouet et al., Reference Lozouet, Lesport and Renard2001, pl. 4, fig. 5; Harzhauser, Reference Harzhauser2014). Similarly, Jujubinus dispar Curini-Galletti, Reference Curini-Galletti1983, a recent species found inhabiting the Moroccan part of the Strait of Gibraltar (Gofas et al., Reference Gofas, Le Renard and Bouchet2001), is known to have prominent prosocline axial threads between the spiral cords. J. dwarkaensis, by contrast, shows dominant axial ornamentation crossed by weak spiral threads, making a beaded appearance.
Jujubinus redoniensis Landau, Van Dingenen, and Ceulemans, Reference Landau, Van Dingenen and Ceulemans2017 (see Landau et al., Reference Landau, Van Dingenen and Ceulemans2017, p. 100, pl. 24, figs. 1, 2), a late Miocene (Tortonian) species from northwestern France, exhibits a similar morphology to J. dwarkaensis. However, they again differ in shell surface ornamentation. In J. redoniensis, the earlier whorls bear spiral cords crossed by prosocline axial ribs, forming a reticulate pattern with small tubercles developed at the intersection. While the pattern in J. dwarkaensis is similar, the axial ribs are opisthocline and more dominant, crossed by weak spiral threads to form tubercles at their intersection. In addition, in J. redoniensis, the axial ribs disappear from the third whorl onward, whereas they are present consistently throughout the whorls in J. dwarkaensis.
Genus Gibbula Risso, Reference Risso1824
Type species
Trochus magus Linnaeus, Reference Linnaeus1758 (= Gibbula magus (Linnaeus, Reference Linnaeus1758)) (by subsequent designation, Linnaeus, Reference Linnaeus1758), Recent, Mediterranean.
Gibbula sp.
Materials
One poorly preserved specimen (ISI/dwk/TDAG/38/i). The specimens were collected from Bulk 3 of Loc. 2 (Fig. 1).
Occurrence
Early Miocene (Burdigalian), Dwarka Basin, Gujarat, India.
Description
Small, moderately thick, turbiniform shell. The shell is depressed with shell diameter (D = 4.32 mm) greater than shell height (H = 3.28 mm). The shell is cyrtoconic with apical angle 89° and pleural angle 94°. Protoconch is not preserved, and the teleoconch consists of four whorls of completely convex whorl profile. Suture is weakly impressed. Ornamentation of the shell is indiscernible and appears to be smooth. The base is convex with no ornamentation visible and can be marked by the presence of a depressed, filled up umbilical notch. The aperture is subquadrate, with the base of the aperture slightly curved.
Remarks
The specimen is poorly preserved, and as a result, its assignment to the genus Gibbula Risso, Reference Risso1824 is based solely on the overall shell shape, nature of the suture, convex whorl profile, and basal characteristics (see Risso, Reference Risso1824; p. 134). The shell shows resemblance to the type species Gibbula magus (Linnaeus, Reference Linnaeus1758) in terms of turban-shaped shell, four to five convex teleoconch whorls, impressed suture, convex base, and presence of an umbilicus (see description in Da Costa, Reference Da Costa1778, p. 44).
The shell outline is comparable to Gibbula poippigii Philippi, Reference Philippi1887, a Miocene species from Chile (described by Nielsen et al., Reference Nielsen, Frassinetti and Bandel2004, p. 81, figs. 37, 38). However, G. poippigii is distinguished by six distinct spiral sculptures on the shell surface, which are not discernible in our specimen. The lack of any diagnostic features hinders a more specific identification of the specimen.
Family Colloniidae Cossmann and Peyrot, Reference Cossmann and Peyrot1917
Subfamily Colloniinae Cossmann and Peyrot, Reference Cossmann and Peyrot1917
Genus Neocollonia Kuroda and Habe, Reference Kuroda and Habe1954
Type species
Neocollonia pilule (Dunker, Reference Dunker1860) (type species by original designation), Recent, Japan.
Neocollonia aff. N. pseudomunda (Harzhauser, Reference Harzhauser2014)
Synonymy list
See Appendix 1.
Materials
One poorly preserved broken specimen (ISI/dwk/TDAG/34/i) with shell preserved. The specimen is collected from Bulk 1 of Loc. 1 (Fig. 1).
Occurrence
Early Miocene (Burdigalian), Dwarka Basin, Gujarat and Quilon Basin, Kerala, India.
Description
Small, moderately thick shell, turbiniform in shape. Protoconch is not preserved. Four teleoconch whorls are preserved. Shell height 3.68 mm and shell diameter 4.20 mm. The whorl profile is subdivided into a slightly sloping sutural ramp and a convex flank. Sutures are narrow and incised. The ramp and flank are separated by a sharp angulation marked by a strong spiral rib. Shell ornamented by three dominant spiral ribs, one at the junction of the ramp and the flank and the other two at the flank. In the last whorl, the third spiral rib separates the flank from the weakly convex base. Fine secondary spiral lirae are present on the ramp and between the dominant spiral ribs, but they are faintly visible in the specimen. A major portion of the basal part and aperture of the shell is broken.
Remarks
Neocollonia pseudomunda (Harzhauser, Reference Harzhauser2014) was previously known from Channa Kodi Section, Warkalli Formation (Burdigalian) in the Quilon Basin, Kerala, India (Harzhauser, Reference Harzhauser2014, p. 81, plate. 1, figs. 8–13). The specimen reported here strongly resembles this South Indian species in terms of overall shell shape and size, shell ornamentation, the number of strong spiral ribs, and the circular aperture. However, due to the broken condition of the specimen, a definite assignment to Neocollonia pseudomunda is not possible.
Subclass Caenogastropoda Cox, Reference Cox1960
Cohort Sorbeoconcha (Ponder and Lindberg, Reference Ponder and Lindberg1997)
Subcohort Campanilimorpha (Haszprunar, Reference Haszprunar1988)
Superfamily Campaniloidea Douvillé, Reference Douvillé1904
Family Ampullinidae Cossmann and Peyrot, Reference Cossmann and Peyrot1919
Subfamily Globulariinae Wenz, Reference Wenz and Schindewolf1941
Genus Globularia Swainson, Reference Swainson1840
Type species
Ampullaria sigaretina Lamarck, Reference Lamarck1804, Eocene, Paris Basin.
Globularia cf. G. carlei (Finlay, Reference Finlay1927)
Figure 11. (1, 2) Globularia cf. G. carlei (Finlay, Reference Finlay1927), specimen number ISI/dwk/TDAG/31/i: (1) abapertural view; (2) apertural view. (3) Cerithoidea fam. indet. gen. indet. sp. indet., specimen number ISI/dwk/TDAG/35/I, apertural view. (4) Cerithiidae gen. indet. sp. indet., specimen number ISI/dwk/TDAG/41/I, apertural view. (5, 6) Cerithium bardhani n. sp., specimen number ISI/dwk/TDAG/23/i (holotype): (5) abapertural view; (6) apertural view. (7, 8) Cerithidium sp., specimen number ISI/dwk/TDAG/24/i: (7) abapertural view; (8) apertural view. (9, 10) Ptychopotamides sp., specimen number ISI/dwk/TDAG/36/i: (9) abapertural view; (10) apertural view. (11, 12) ?Cyrillia sp., specimen number ISI/dwk/TDAG/45/i: (11) apertural view; (12) abapertural view. (1, 2) Scale bars = 5 mm; (3–12) scale bars = 1 mm.
Synonymy list
See Appendix 1.
Materials
Two poorly preserved specimens (ISI/dwk/TDAG/31/i, ii), internal molds. The specimens were collected from Bulk 2 of Loc. 1 (Fig. 1).
Occurrence
Miocene of Kutch and Dwarka basins, India; Miocene of Kenya.
Description
Shell medium in size, globose in shape, phaneromphalous. Shell height and diameter nearly equal (maximum height = 18.03 mm; maximum diameter = 17.44 mm). Pleural angle ranging from 95° to 99°. Shell comprises four whorls. Spire very low, and body whorl enveloping the preceding whorls. Suture is adpressed. Shell surface smooth. Base is convex, and umbilicus is indiscernible. Aperture is ear shaped with the adapical part of the aperture reaching close to the spire. Base of the aperture is convex.
Remarks
Although the specimens described here are internal molds, they show noteworthy resemblance to the Globularia carlei (Finlay, Reference Finlay1927) (see Harzhauser et al., Reference Harzhauser, Reuter, Piller, Berning, Kroh and Mandic2009, p. 338, fig. 2c, d; Kulkarni et al., Reference Kulkarni, Kapoor and Borkar2010, p. 327–328, fig. 3b; Jain, Reference Jain2014, p. 140–141, pl. 32, figs. 11, 12, 15, 16) in several aspects such as globose shell shape, number of whorls, low spire, adpressed suture, ear-shaped aperture with its adapical part reaching the spire, and convex base.
Subcohort Cerithiimorpha Golikov and Starobogatov, Reference Golikov and Starobogatov1975
Superfamily Cerithioidea Fleming, Reference Fleming1822
Cerithioidea fam. indet. gen. indet. sp. indet.
Materials
One very poorly preserved specimen (ISI/dwk/TDAG/35/i) with partial shell preserved. The specimen is collected from Bulk 2 of Loc. 1 (Fig. 1).
Occurrence
Early Miocene (Burdigalian), Dwarka Basin, Gujarat, India.
Description
Shell small, stout, and pupoid in shape. Shell higher than broad, with shell height 6.49 mm and shell diameter 3.31 mm. The shell has a cyrtoconic spire with pleural angle 30°. Spire consists of five whorls. Suture is indiscernible. Prominent spiral folds present as ornamentation, making the whorls telescoped in profile. The ornamentation of the body whorl is characterized by faintly visible six spiral lirae. The shell is anomphalous with basal features indiscernible as well. Aperture is broken.
Remarks
The species shows resemblances to modern representatives of the superfamily Cerithioidea, particularly in its pupoid shell outline, convex whorls, and basal features (Strong et al., Reference Strong, Colgan, Healy, Lydeard, Ponder and Glaubrecht2011). However, the specimen is notably different from other Miocene cerithioid species of the Indian subcontinent in terms of the shell outline and surface ornamentation.
Family Cerithiidae Fleming, Reference Fleming1822
Cerithiidae gen. indet. sp. indet.
Materials
Four very poorly preserved specimens (ISI/dwk/TDAG/41/i–iv). ISI/dwk/TDAG/41/i is the figured specimen. The specimens are collected from Bulk 1 (one specimen: ISI/dwk/TDAG/41/i) and Bulk 2 (three specimens) of Loc. 1 (Fig. 1).
Occurrence
Early Miocene (Burdigalian), Dwarka Basin, Gujarat, India.
Description
Shell small, slender, and pupoid in shape. Much higher than broad (H = 5.62 mm and D = 2.54 mm). Four to five whorls preserved. Cyrtoconic shell with weakly convex rugose whorl profile, and pleural angle of the shell is 25°. Suture is flushed. Ornamentation of the shell marked by faintly visible spiral threads that are crosscut by axial ribs producing small nodes. Shell is anomphalous. Base is smooth, and aperture is not properly preserved.
Remarks
The specimens described here are incomplete and poorly preserved, showing only four to five whorls and a broken aperture. Despite their condition, they exhibit similarities to the representative species of family Cerithiidae in terms of overall shell shape and ornamentation (Fleming, Reference Fleming1822). Notable characters are slender pupoid shell, surface ornamentation having spiral threads that intersect axial folds creating nodes at the intersections. These characters are reminiscent of Cerithium (?Chondrocerithium) bhagothorense of Sindh, Pakistan, as described by Vredenburg (Reference Vredenburg1928, p. 361, pl. 15, figs. 1, 2).
Subfamily Cerithiinae Fleming, Reference Fleming1822
Genus Cerithium Bruguière, Reference Bruguière1789
Type species
Cerithium adansonii Bruguière, Reference Bruguière1789 (type species by original designation), Recent, Indo-Pacific.
Cerithium bardhani new species
Holotype
Specimen no. ISI/dwk/TDAG/23/i. Nandana Shale–Siltstone Unit, Nandana Member, Gaj Formation, Dwarka Basin, India, early Miocene (Burdigalian).
Materials
One moderately well-preserved specimen (ISI/dwk/TDAG/23/i) with shell preserved is figured. The specimen is collected from Bulk 1 of Loc. 1 (Fig. 1).
Diagnosis
Shell ornamented with 15 axial ribs intersecting four spiral ribs, forming small tubercles at their intersection. The anterior spiral in the body whorl does not have any tubercle. Tubercles get stronger in the posterior end.
Occurrence
Early Miocene (Burdigalian), Dwarka Basin, Gujarat, India.
Description
Shell small, slender, cerithiform in shape. Much higher than broad with shell height 4.29 mm and shell diameter 2.07 mm. Shell is cyrtoconic with apical angle 34° and pleural angle 28°. Protoconch is not preserved. Teleoconch consists of five slightly convex whorls. Suture is flushed. Early teleoconch whorls ornamented by regularly spaced axial ribs, which become more widely spaced in later whorls. The axial ribs are crosscut by low spiral ribs. Body whorl marked by 15 axial ribs and four spiral ribs. Small tubercles are formed at the intersection of the spiral and axial element, which are much more prominent in strength along the first spiral and subsequently weaken along the later spirals. The anteriormost spiral on the body whorl is smooth and bears no tubercle. Shell is anomphalous. Base is partly broken, and thus, basal features and apertural outline are not clearly discernible. However, there is a small hint of siphonal notch present at the anterior end of the shell.
Etymology
Named in honor of Indian paleontologist Prof. Subhendu Bardhan.
Remarks
The species Cerithium bardhani n. sp. is assigned to Cerithium due to its resemblance to the forms and other morphological characters of modern representatives of the genus (see Houbrik, Reference Houbrick1992; Russo and Quaggiotto, Reference Russo and Quaggiotto2016).
Cerithium bardhani exhibits a distinctive shell surface ornamentation that is uncommon among early Miocene Cerithium species. It is comparable to Cerithium deningeri Martin, Reference Martin1916, an early Miocene (Burdigalian) species from Java, Indonesia (see Reich et al., Reference Reich, Wesselingh and Renema2014, p. 17, pl. 3, fig. 6) in terms of overall shell outline. However, C. deningeri lacks the tubercles formed at the intersections of the axial and the spiral elements, which are present in C. bardhani.
Cerithium vulgatum Bruguière, Reference Bruguière1789, a recent species in the Mediterranean Sea (see Russo and Quaggiotto, Reference Russo and Quaggiotto2016, p. 18, fig. 1), features a gradated whorl profile with each whorl ornamented by 12–13 axial ribs and the shoulder marked by a row of nodes at the posterior end of each axial rib. In C. bardhani, the whorls are slightly convex, and the ornamentation displays tubercles at the intersections of the spiral and axial ribs, which are more prominent on the posterior side and gradually weaken toward the anterior.
Subfamily Bittiinae Cossmann, Reference Cossmann1906
Genus Cerithidium di Monterosato, Reference di Monterosato1884
Type species
Cerithidium submammillatum (de Rayneval, van den Hecke, and Ponzi, Reference de Rayneval, Le, van den Hecke and Ponzi1854) (type by monotypy), Pleistocene, Mediterranean Sea.
Cerithidium sp.
Materials
Three moderately to poorly preserved specimens (ISI/dwk/TDAG/24/i–iii). ISI/dwk/TDAG/24/i is the figured specimen. The specimens are collected from Bulk 1 of Loc. 1 (Fig. 1).
Occurrence
Early Miocene (Burdigalian), Dwarka Basin, Gujarat, India.
Description
Shell is small, thin, and turreted in shape with shell height 5.28 mm and shell diameter 2.16 mm. The shell is cyrtoconic with apical angle 35° and pleural angle 28°. Protoconch is preserved and has about one and three quarters of moderately convex and smooth whorls. The teleoconch consists of six whorls characteristically having a highly keeled nodulated shoulder with a nearly flat ramp and slightly convex flanks. Suture is flushed. The first whorl of the teleoconch is marked by three faintly visible spiral lirae. The successive whorls display axial ribs crosscut by faintly visible spirals. The body whorl is characterized by 12 regularly spaced strong axial ribs and four prominent spiral threads (one on the ramp, one along the shoulder, and two on the flank). The spirals positioned on the shoulder and immediately below the shoulder prominently form small nodes at their intersection with the axial ribs, resulting in a nodular appearance of the whorls. Shell is anomphalous with a slightly curved base. However, the basal ornamentation is not discernible. Aperture is subcircular with a thin corrugated outer lip.
Remarks
The specimens show some resemblance to the lower Miocene (Aquitanian) species Cerithidium plebeium Lozouet, Reference Lozouet1998 (see Lozouet, Reference Lozouet1998, p. 88–89, fig. 14j, k) in terms of overall shell shape, smooth and convex protoconch, shape of the aperture, and shell surface ornamentation. However, there are notable differences: C. plebeium features two spiral cords on the first whorl, whereas Cerithidium sp. have three spiral lirae. In addition, C. plebeium has a deeply grooved suture while in Cerithidium sp., the suture is flushed.
Family Potamididae Adams and Adams, Reference Adams and Adams1854
Genus Ptychopotamides Sacco, Reference Sacco1895
Type species
Ptychopotamides tricinctus (Brocchi, Reference Brocchi1814) (type by original designation). Pliocene, Northern Europe.
Ptychopotamides sp.
Materials
Eleven moderately to poorly preserved specimens (ISI/dwk/TDAG/36/i–xi). ISI/dwk/TDAG/36/i is the figured specimen. The specimens are collected from Bulk 1 (nine specimens) and Bulk 2 (two specimens) of Loc. 1 (Fig. 1).
Occurrence
Early Miocene (Burdigalian), Dwarka Basin, Gujarat, India.
Description
Shells are small, slightly compressed, turreted in shape. Shell much higher than broad (H = 5.46 mm and D = 2.24 mm). Protoconch is missing for all the specimens. The spire consists of at most four to five teleoconch whorls. The overall shell is cyrtoconic; however, the whorl profile is nearly straight with apical angle 35°–37° and pleural angle 27°–29°. Suture is shallow, linear, and slightly impressed. Ornamentation is well preserved and marked by 15 straight to slightly oblique axial ribs, which are separated by moderately wide interspaces. Four spiral threads of equal strength crosscut these axial ribs making a granular appearance at their intersection. Aperture is small and subcircular. The base is marked by two prominent spiral ribs and a siphonal notch at the anteriormost end. Shell is anomphalous with a slightly thickened columellar lip.
Remarks
Ptychopotamides sp. shows similarity with Ptychopotamides tricinctus (Brocchi, Reference Brocchi1814), a late Miocene–Pliocene species from the Mediterranean and northern Europe (Wesselingh et al., Reference Wesselingh, Rijken, van Nieulande, Janse and Pouwer2012, p. 44, fig. 34), particularly in terms of its flat whorl profile, shell surface ornamentation with three to four spiral ribs making very low cusps at the intersection to axial ribs, and a shallow sinus at the base. However, Ptychopotamides sp. differs in having straight to slightly oblique axial ribs on the whorl surface and a shallow slightly impressed suture, whereas P. tricinctus is characterized by prosocline to inverted C-shaped axial ribs and a deep and incised suture.
Genus Vicarya d’Archiac and Haime, Reference d’Archiac and Haime1854
Type species
Vicarya tyosenica Yabe and Hatai, Reference Yabe and Hatai1938, Miocene, Japan.
Vicarya cf. V. verneuili (d’Archiac, Reference d’Archiac1850)
Figure 12. (1) Vicarya cf. V. verneuili (d’Archiac, Reference d’Archiac1850), specimen number ISI/dwk/TDAG/1/I, abapertural view. (2–4) Scaliola subbela Harzhauser, Reference Harzhauser2014: (2) specimen number ISI/dwk/TDAG/14/I, apertural view; (3) specimen number ISI/dwk/TDAG/14/ii, apertural view; (4) specimen number ISI/dwk/TDAG/14/iii, abapertural view. (5–7) Finella sp.: (5, 6) specimen number ISI/dwk/TDAG/25/i: (5) abapertural view; (6) apertural view; (7) specimen number ISI/dwk/TDAG/25/ii, abapertural view. (8, 9) Turritella angulata Sowerby, Reference Sowerby1840, specimen number ISI/dwk/TDA/1/i: (8) abapertural view; (9) apertural view. (10, 11) Haustator cf. H. tauroperturritus Sacco, Reference Sacco1895, specimen number ISI/dwk/TDA/4/i: (10) abapertural view; (11) apertural view. (1, 8–11) Scale bars = 10 mm; (2) scale bar = 1 mm; (3–7) scale bars = 500 μm.
Synonymy list
See Appendix 1.
Materials
Twenty-three moderately to poorly preserved, broken to nearly complete specimens (ISI/dwk/TDAG/1/i–xxiii). ISI/dwk/TDAG/1/i representing the adult form of the species is the figured specimen. The specimens were collected from Bulk 1 (15 specimens) and Bulk 2 (7 specimens) of Loc. 1 (Fig. 1).
Occurrence
Miocene: Iran, Pakistan, India, Indonesia, Philippines, Korea, and Japan.
Description
Shell thin, large (adult form), compressed, and turreted in shape. Shell is much higher than broad with maximum shell height 53.20 mm and maximum shell diameter 28.98 mm. Apical angle is 39°–42° and pleural angle is 43°–46°. Protoconch partly preserved in a single juvenile specimen having one smooth rounded whorl. The spire of the adult specimen consists of nine teleoconch whorls that are slightly convex to straight walled. Suture is weakly incised. The shell is ornamented by at least four spiral cords with the spiral positioned posterior of the whorl, displaying a row of widely spaced nodes, which get much larger and more prominent in the later whorls. Below that, the rest of the spiral cords are densely spaced and characterized by beady to smooth appearance. The base and aperture are not preserved.
Remarks
Although the specimens are moderately to poorly preserved, their general shell outline and shell surface sculpture strongly align with the description of Vicarya verneuili d’Archiac, Reference d’Archiac1850 as described by d’Archiac and Haime (Reference d’Archiac and Haime1854). They show a resemblance to the early Miocene specimens of Vicarya verneuili from the Dwarka Basin described and illustrated by Jain (Reference Jain2014, p. 129, pl. 28, figs. 30, 31, pl. 38, figs. 18, 19). However, since important generic characters such as aperture and base of the shell are not preserved, definite assignment to this species is not possible.
Family Scaliolidae Jousseaume, Reference Jousseaume1912
Genus Scaliola Adams, Reference Adams1860
Type species
Scaliola bella Adams Reference Adams1860, Recent, Indo–West Pacific.
Scaliola subbela Harzhauser, Reference Harzhauser2014
Figures 12.2–12.4, 13.10–13.12
Figure 13. (1, 2) Mitridae gen indet. Sp. indet., specimen number ISI/dwk/TDA/17/ii: (1) abapertural view; (2) apertural view. (3–5) ?Alocospira sp.: (3, 4) specimen number ISI/dwk/TDA/29/i: (3) abapertural view; (4) apertural view; (5) specimen number ISI/dwk/TDA/29/ii, apertural view. (6, 7) Conus sp., specimen number ISI/dwk/Nm/13/12: (6) apertural view; (7) apical view. (8, 9) Retusidae gen. indet. sp. indet., specimen number ISI/dwk/TDA/18/ii: (8) apertural view; (9) dorsal view. (10–12) Scaliola subbela Harzhauser, Reference Harzhauser2014: (10) specimen number ISI/dwk/TDA/20/I, abapertural view; (11, 12) specimen number ISI/dwk/TDA/20/ii: (11) apertural view; (12) abapertural view. (1, 2, 8–12) Scale bars = 500 μm; (3–5) scale bars = 1 mm; (6, 7) scale bars = 5 mm.
Synonymy list
See Appendix 1.
Hypotype
Specimen number ISI/dwk/TDAG/14/ i. Nandana Shale–Siltstone Unit, Nandana Member, Gaj Formation, Dwarka Basin, India, early Miocene (Burdigalian).
Materials
Twenty-three moderately well to poorly preserved complete to near-complete specimens (ISI/dwk/TDAG/14/i–vii; ISI/dwk/TDAG/20/i–xvi) with shell preserved and nine broken fragments collected. ISI/dwk/TDAG/14/ i, ii and ISI/dwk/20/i, ii are the figured specimens. The specimens are collected from Bulk 1 (20 complete specimens and three broken fragments) and Bulk 2 (three complete specimens and one broken fragment) of Loc. 1 and Bulk 3 (five broken fragments) collection of Loc. 2 (Fig. 1).
Occurrence
Early Miocene (Burdigalian), Quilon, Kerala, and Dwarka, Gujarat, India.
Description
Shell minute to small, quite slender, turreted in shape. Shell is higher than broad with maximum shell height 5.72 mm and maximum shell diameter 2.83 mm. Shell is slightly cyrtoconic with apical angle 26°–27°. Spire is high with protoconch consisting of nearly two whorls whereas the teleoconch comprises about three to four whorls. Protoconch whorls are smooth and well rounded with a weakly angulated shoulder. The teleoconch whorls have uniformly convex profile, shell surface appears mostly smooth; however, very faint spiral lirae are visible and are separated by moderately wide, deeply incised suture. The whorl surface mostly covered by sediments. Uncoiling tendency can be observed from the penultimate whorl with the body whorl slightly detached. Shell is anomphalous. Aperture is oval, with the inner lip almost straight and protruding inward. However, outer lip and base are thin and nearly curved in outline.
Remarks
The specimens described here have a mostly smooth shell surface with presence of very faint spiral lirae. They are comparable to the Quilon forms of the species described by Harzhauser (Reference Harzhauser2014), which exhibit weak spiral threads between the particles densely covering the shell (see Harzhauser, Reference Harzhauser2014; p. 89–90, pl. 3, fig. 13). In addition, the specimens show a striking similarity to Scaliola subbella Harzhauser, Reference Harzhauser2014 in terms of their overall slender shell outline, characteristics of the protoconch, uncoiling of the last whorl, and the elongated subcircular aperture. These features securely place our specimens within this species.
Genus Finella Adams, Reference Adams1860
Materials
Three very poorly preserved specimens (ISI/dwk/TDAG/25/i–iii). ISI/dwk/TDAG/25/i is the figured specimen. The specimens were collected from Bulk 1 (two specimens) and Bulk 2 (one specimen) of Loc. 1 (Fig. 1).
Occurrence
Early Miocene (Burdigalian), Quilon, Kerala, and Dwarka, Gujarat, India.
Description
Shell small, moderately thick, overall pupoid shaped, and comprising a moderately high spire (maximum H = 4.38 mm; maximum D= 3 mm). The shell is cyrtoconic with apical angle 48°–50°. Protoconch is partly preserved and consists of one and a half smooth whorls. The teleoconch consists of four convex whorls. Suture is impressed. The first and the second whorls of the teleoconch display a single spiral thread running along the mid part of the shell. The later whorls are sculptured by faintly visible sharp axial threads that are interrupted by a spiral band positioned posteriorly. The spiral appears considerably noded and is followed by a prominent median spiral thread. Thereafter, a less prominent spiral thread is present along the lower suture. Shell is anomphalous. Base of the shell is slightly convex and sculptured by three prominent spiral lirae. Aperture is ovate with slight posterior angulation.
Remarks
The specimens described here show notable resemblance to the paratype specimen of Finella bruchae Harzhauser, Reference Harzhauser2014 from Quilon, as described and illustrated in Harzhauser (Reference Harzhauser2014, pl. 4, fig. 2). This resemblance is evident in terms of the overall shape of the shell, the number of protoconch and teleoconch whorls, the whorl profile, suture, shell ornamentation, and the shape of the aperture. The specimens lack any prominent grooves or furrows below the upper suture, and the base is marked by only three prominent spiral lirae, whereas the Quilon species has six spiral threads. Due to the poor preservation of our specimens, a definitive assignment to this species is not possible.
Family Turritellidae Lovén, Reference Lovén1847
Subfamily Turritellinae Lovén, Reference Lovén1847
Genus Turritella Lamarck, Reference Lamarck1799
Type species
Turbo terebra Linnaeus, Reference Linnaeus1758. Recent, Indo–Pacific.
Turritella angulata Sowerby, Reference Sowerby1840
Figure 14. (1) Scanning electron micrographs of apex of Turritella angulata Sowerby, Reference Sowerby1840 (specimen number ISI/dwk/TDA/1/a) showing early teleoconch part and well-developed apical sculpture. (2) Magnified view of rectangular area in (1). (3) Line diagram of (2) showing primary spiral ribs. (4) Scanning electron micrographs of apices of Turritella pseudotethis Vredenburg, Reference Vredenburg1928 (specimen number ISI/dwk/TDA/7/a) showing early teleoconch part and well-developed apical sculpture. (5) Magnified view of rectangular area in (4). (6) Line diagram of (5) showing primary spiral ribs. The primary spirals are A, B, C, d (notation after Allmon, Reference Allmon1996). st = suture. (1, 4) Scale bars = 0.5 mm; (2, 3, 5, 6) scale bars = 200 μm.
Synonymy list
See Appendix 1.
Hypotype
Specimen number ISI/dwk/TDA/01/1. Nandana Shale–Siltstone Unit, Nandana Member, Gaj Formation, Dwarka Basin, India, early Miocene (Burdigalian).
Materials
A total of 1,234 well to moderately well-preserved specimens (ISI/dwk/TDA/01/1–1234). ISI/dwk/TDA/01/1 is the figured specimen. The specimens are from Bulk 1, Bulk 2, and random collections of Loc. 1 (1,082 specimens); Bulk 3 and random collections of Loc. 2 (80 specimens); and random collections of Loc. 3 (72 specimens) (Fig. 1).
Occurrence
Miocene of Kutch and Dwarka basins, India, and Sindh, Pakistan. Miocene of Meghalaya, India, and Myanmar, Java, Egypt, and Arabia. Miocene of Karaibari Hills, Bengal. Pliocene of Java and Karikal Beds, India. Makran Series (Talar Stage), Talar Gorge, Baluchistan, Makran, Pakistan. Recent, Indian Ocean.
Remarks
The shell is medium to large, turreted in shape, and made up of approximately eight whorls. Protoconch is smooth and has about two and a half whorls. The maximum observed whorl diameter is 22.82 mm, and maximum observed whorl height is 57.45 mm. Pleural angle ranges from 27° to 35°. Suture is shallow and impressed. Shell is characterized by four primary spirals (A, B, C, and D). The third (C) primary spirals appear at the first in early ontogeny, followed by the first and second primary spirals (A and B) occurring simultaneously, and lastly followed by the fourth (D). The apical sculpture formula is C1B2A2d3 (Fig. 14.1–14.3). Spiral A is situated at the upper third of the whorls, spiral B is situated at or below the mid whorl, and the last two spirals (C and D) are situated at the anterior of the third spiral. The strength of the primary spirals increases with the ontogeny with the most prominent being spiral C, which gets considerably angular in subsequent whorls. Two secondary spirals are situated above spiral A, one between A and B, and two between C and D. Faint opisthocyrt growth lines are visible on the shell surface (Fig. 14.1, 14.2). The whorl profile at early ontogeny is keeled and gradually gets campanulate to hyper-campanulate in the adult whorls. Base of the shell is convex, and the aperture is subcircular.
These features show a striking similarity to the common Miocene turritelline species Turritella angulata Sowerby, Reference Sowerby1840. The specimens conform with the figures provided by Harzhauser et al., (Reference Harzhauser, Reuter, Piller, Berning, Kroh and Mandic2009, p. 343–344, figs. 3a–d) and Jain (Reference Jain2014, p. 134–136, pl. 27, figs. 12–19), and is therefore assigned to this species.
Turritella narica Vredenburg, Reference Vredenburg1928
Figure 15. (1, 2) Turritella narica Vredenburg, Reference Vredenburg1928, specimen number ISI/dwk/TDA/2/i: (1) abapertural view; (2) apertural view. (3, 4) Turritella pseudotethis Vredenburg, Reference Vredenburg1928: (3) specimen number ISI/dwk/TDA/7/ii abapertural view; (4) specimen number ISI/dwk/TDA/7/ii, apertural view. (5, 6) Turritella assimilis Sowerby, Reference Sowerby1840, specimen number ISI/dwk/TDA/3/i: (5) abapertural view; (6) apertural view. (7, 8) Turritella bhagothorensis Vredenburg, Reference Vredenburg1928, specimen number ISI/dwk/TDA/5/i: (7) abapertural view; (8) apertural view. (9, 10) Turritella kachhensis Vredenburg, Reference Vredenburg1928, specimen number ISI/dwk/TDA/8/i: (9) abapertural view; (10) apertural view. (11, 12) Turritella pseudobandogensis Vredenburg, Reference Vredenburg1928, specimen number ISI/dwk/TDA/6/i: (11) abapertural view; (12) apertural view. Scale bars = 10 mm.
Figure 16. (1) Scanning electron micrograph of apex of Turritella kacchensis Vredenburg, Reference Vredenburg1928 (specimen number ISI/dwk/TDA/8/a) showing early teleoconch part and well-developed apical sculpture. (2) Magnified view of rectangular area in (1). (3) Line diagram of (2) showing primary spiral ribs. (4, 7) Scanning electron micrographs of apices of Turritella narica Vredenburg, Reference Vredenburg1928 (specimen numbers ISI/dwk/TDA/2/a, b) showing early teleoconch part and well-developed apical sculpture. (5) Magnified view of rectangular area in (4). (8) Magnified view of rectangular area in (7). (6) Line diagram of (5) showing primary spiral ribs. (9) Line diagram of (8) showing primary spiral ribs. The primary spirals are A, B, C (notation after Allmon, Reference Allmon1996). st= suture. (1, 7) Scale bars = 0.5 mm; (2, 3, 8, 9) scale bars = 200 μm; (4) scale bar = 300 μm; (5, 6) scale bars = 100 μm.
Synonymy list
See Appendix 1.
Hypotype
Specimen number ISI/dwk/TDA/2/1. Nandana Shale–Siltstone Unit, Nandana Member, Gaj Formation, Dwarka Basin, India, early Miocene (Burdigalian).
Materials
Seven hundred thirty-eight well-preserved specimens (ISI/dwk/TDA/2/1–738). The specimens are from Bulk 1, Bulk 2, and random collections of Loc. 1 (608 specimens); Bulk 3 and random collections of Loc. 2 (113 specimens); and random collections of Loc. 3 (17 specimens) (Fig. 1).
Occurrence
Oligocene of Baluchistan and Sindh (Pakistan), Miocene of Dwarka Basin (India).
Remarks
The specimens are medium in size and turreted in shape. The maximum whorl diameter is 12.05 mm, and maximum whorl height is 30.21 mm. Shells have approximately six to seven whorls. Pleural angle ranges from 23° to 26°. Protoconch is preserved. Suture is shallow and impressed. Shell surface is ornamented by three prominent spiral threads, and three secondary spirals are present between the primary spirals. The first primary spiral (A) appears first in the early ontogeny, followed by the second (B) and third (C) primary spirals. The apical sculpture formula is A1B2C3 (Fig. 16.4–16.9). The second primary spiral is the most prominent one, situated just below the mid-whorl, and shows sharp angularity. The strength of the second primary spiral gradually increases in later ontogeny. Whorl profile is convex to frustrate in nature. Faint prosocyrt growth lines are seen on the shell surface. Base is slightly convex and carinated by two definite spirals. Aperture is circular in shape.
These features closely resemble Turritella narica Vredenburg, Reference Vredenburg1928, as illustrated and described by Vredenburg (Reference Vredenburg1928, p. 375, pl. 18, figs. 13–17, pl. 19, figs. 2, 6) and Jain (Reference Jain2014, p. 132–133, pl. 28, figs. 9–17), leading to their assignment to this species.
Turritella assimilis Sowerby, Reference Sowerby1840
Figure 17. Scanning electron micrographs of apices of Turritella assimilis Sowerby, Reference Sowerby1840. (1) Specimen number ISI/dwk/TDA/3/a, showing early teleoconch part and well-developed apical sculpture. (2) Magnified view of rectangular area in (1). (3) Line diagram of (2) showing primary spiral ribs. (4) Specimen number ISI/dwk/TDA/3/b, showing early teleoconch part and well-developed apical sculpture. (5) Magnified view of rectangular area in (4). (6) Line diagram of (5) showing primary spiral ribs. The primary spirals are A, B, C; secondary spirals are r, s (notation after Allmon, Reference Allmon1996). st = suture. (1, 4) Scale bars = 0.5 mm; (2, 3, 5, 6) scale bars = 200 μm.
Synonymy list
See Appendix 1.
Hypotype
Specimen number ISI/dwk/TDA/3/1. Nandana Shale–Siltstone Unit, Nandana Member, Gaj Formation, Dwarka Basin, India, early Miocene (Burdigalian).
Materials
A total of 2,848 well-preserved specimens (specimen number ISI/dwk/TDA/3/1–2848). The specimens are collected from Bulk 1, Bulk 2, and random collections of Loc. 1 (2,634 specimens); Bulk 3 and random collections of Loc. 2 (208 specimens) (Fig. 1; see Materials and methods for locality details).
Occurrence
Early Miocene (Burdigalian) of the Kutch and Dwarka basins (India).
Remarks
The specimens are medium in size, turreted in shape, and have approximately nine to 10 whorls. Protoconch is preserved. The maximum whorl diameter is 8.49 mm, and maximum whorl height is 20.82 mm. The pleural angle ranges from 23° to 26°. Suture is moderately incised and impressed. Shell surface is ornamented by three prominent spirals (A, B, C), which are of equal strength throughout the ontogeny. Of the two secondary spirals, one (r) occurs between the upper suture boundary and primary spiral A, and the other one (s) is between A and B. The apical sculpture formula is C1 B2 s4 A2 r3 (Fig. 17). Growth lines are faintly visible and are orthocline to opisthocline in nature. Whorl profile is flat to slightly convex. Base is moderately curved, and the aperture is subcircular to circular in shape. The base of the aperture is slightly flat.
These characters conform with the characteristic features of Turritella assimilis Sowerby, Reference Sowerby1840, as redescribed by Harzhauser et al. (Reference Harzhauser, Reuter, Piller, Berning, Kroh and Mandic2009, p. 341, fig. 3j–n). Thus, the specimens are assigned to this species.
Turritella bhagothorensis Vredenburg, Reference Vredenburg1928
Figure 18. (1) Scanning electron micrograph of apex of Turritella bhagothorense Vredenburg, Reference Vredenburg1928 (specimen number ISI/dwk/TDA/5/a) showing early teleoconch part and well-developed apical sculpture. (2) Magnified view of rectangular area in (1). (3) Line diagram of (2) showing primary spiral ribs. The primary spirals are A, B, C (notation after Allmon, Reference Allmon1996). st = suture. (1) Scale bar = 0.5 mm; (2, 3) scale bars = 200 μm.
Synonymy list
See Appendix 1.
Hypotype
Specimen number ISI/dwk/TDA/5/1. Nandana Shale–Siltstone Unit, Nandana Member, Gaj Formation, Dwarka Basin, India, early Miocene (Burdigalian).
Materials
Six hundred well-preserved specimens (ISI/dwk/TDA/5/1–600). The specimens are from Bulk 1, Bulk 2, and random collections of Loc. 1 (595 specimens); Bulk 3 and random collections of Loc. 2 (five specimens) (Fig. 1).
Occurrence
Oligocene of Sindh, Pakistan, and Miocene of Dwarka Basin, India.
Remarks
The specimens are medium to small, turreted in shape, and have approximately seven to eight whorls. Protoconch preserved and has two smooth whorls. The maximum whorl diameter is 4.94 mm, and maximum whorl height is 16.46 mm. The pleural angle ranges from 21° to 25°. Suture is grooved. The shell surface is ornamented by three primary spirals (A, B, and C) with apical sculpture formula C1A2B3 (Fig. 18). The first spiral (A) is the most dominant one throughout the later ontogeny. It shows sharp angulation and is situated at the upper third of the whorl, resulting in the whorls having a telescoped whorl profile. The second primary spiral is situated at or below the mid-whorl and is of intermediate strength, resulting in a slightly keeled profile in the mid-whorl. However, for most of the specimens, the mid-whorl is straight in profile. The third primary spiral is present immediately above the lower suture and is weakest in strength. Six secondary spirals are present, one above the first primary spiral, four between first and second primary spirals, and one between the third primary spiral and the lower suture. Faint opisthocyrt growth lines are visible on the shell surface. Base is flat to slightly curved, and the aperture is oval.
These features show striking resemblance to Turritella bhagothorensis Vredenburg, Reference Vredenburg1928 as illustrated by Jain (Reference Jain2014, p. 131–132, pl. 27, figs. 26, 27). Because of these similarities, the specimens are assigned to this species.
Turritella kachhensis Vredenburg, Reference Vredenburg1928
Synonymy list
See Appendix 1.
Hypotype
Specimen number ISI/dwk/TDA/8/1. Nandana Shale–Siltstone Unit, Nandana Member, Gaj Formation, Dwarka Basin, India, early Miocene (Burdigalian).
Materials
Ninety-eight well-preserved specimens (ISI/dwk/TDA/8/1–98). The specimens are from Bulk 1, Bulk 2, and random collections of Loc. 1 (95 specimens); Bulk 3 and random collections of Loc. 2 (three specimens) (Fig. 1).
Occurrence
Miocene of Kutch and Dwarka basins (India).
Remarks
The specimens are medium in size, turreted in shape, and have approximately nine to 10 whorls. Protoconch is preserved. The maximum whorl diameter is 4.29 mm, and maximum whorl height is 13.01 mm. The pleural angle ranges from 21° to 28°. Suture is deep, grooved, and narrow in width. Shell surface is sculptured by three spirals (A, B, and C) of which the first two spirals (A, B) are very closely spaced and lie very close to the upper suture. The third spiral (C) is situated close to the lower suture boundary. The first and third spirals are prominent and are of equal strength, and the intermediate spiral is of comparatively weaker strength. The apical sculpture formula is C1A2B2 (Fig. 16.1–16.3). The central part of the whorl face is smooth or occasionally bears secondary spiral threads in some specimens. The whorl profile is concave. Base of the shell is flat, and aperture is small and circular.
These show a strong resemblance to Turritella kachhensis Vredenburg, Reference Vredenburg1928 as described by Harzhauser et al. (Reference Harzhauser, Reuter, Piller, Berning, Kroh and Mandic2009, p. 341, figs. 3g–i, 5l) and Jain (Reference Jain2014, p. 132, pl. 27, figs. 20, 21) and thus are assigned to this species.
Turritella pseudotethis Vredenburg Reference Vredenburg1928
Synonymy list
See Appendix 1.
Hypotype
Specimen number ISI/dwk/TDA/7/1. Nandana Shale–Siltstone Unit, Nandana Member, Gaj Formation, Dwarka Basin, India, early Miocene (Burdigalian).
Materials
Four hundred eighty-one well-preserved specimens (ISI/dwk/TDA/7/1–481). The specimens are from Bulk 1, Bulk 2, and random collections of Loc. 1 (471 specimens); Bulk 3 and random collections of Loc. 2 (10 specimens) (Fig. 1).
Occurrence
Oligocene and Miocene of Sindh (Pakistan) and Miocene of Dwarka Basin (India).
Remarks
The specimens are medium in size and turreted in shape. The shells have approximately nine whorls. Protoconch is smooth and has one and a half whorls. The maximum whorl diameter is 8.21 mm, and maximum whorl height is 19.29 mm. Pleural angle ranges from 21° to 27°. Suture is shallow, impressed, and broad in width. The shell surface is ornamented by two primary spirals (A and B), of which the first spiral is situated near the upper suture boundary, and the other one lies near the lower suture boundary. The apical sculpture formula is B1A2 (Fig. 14.4–14.6). The two spirals are most prominent and equal in strength. The interspace between two spirals has one to two very fine secondary spiral threads. Whorl profile is concave, and the base is slightly curved. Aperture is small and circular to subcircular.
The specimens show a strong similarity to Turritella pseudotethis Vredenburg Reference Vredenburg1928 (see type specimens of Vredenburg, Reference Vredenburg1928, p. 380, pl. 21, figs. 2, 8 and Jain, Reference Jain2014, p. 134, pl. 38, figs. 3a, b) and thus are assigned to this species. Although similar in shell ornamentation, Turritella pseudotethis has a shallow, broad impressed suture and differs from Turritella kachhensis, which has a deep, narrow grooved suture.
Turritella pseudobandogensis Vredenburg, Reference Vredenburg1928
Synonymy list
See Appendix 1.
Hypotype
Specimen number ISI/dwk/TDA/6/1. Nandana Shale–Siltstone Unit, Nandana Member, Gaj Formation, Dwarka Basin, India, early Miocene (Burdigalian).
Materials
One hundred ninety-six well-preserved specimens (ISI/dwk/TDA/6/1–196), comprising both intact and broken specimens. ISI/dwk/TDA/6/1 is the figured specimen. The specimens are from Bulk 1, Bulk 2, and random collections of Loc. 1 (184 specimens); Bulk 3 and random collections of Loc. 2 (12 specimens) (Fig. 1).
Occurrence
Gaj of Sindh (Miocene) in Pakistan; early Miocene (Burdigalian) of Dwarka Basin, India.
Remarks
Shell is medium to small, turreted in shape, with maximum height 17.53 mm and maximum diameter 6.55 mm. Pleural angle ranges from 23° to 28°. Protoconch is not preserved, and teleoconch has approximately six whorls. Suture is poorly incised and slightly wide. Whorls are sculptured by four prominent primary spiral threads although variable in strength, followed by around four to five secondary spirals between the primary spirals. Whorl profile is nearly convex. Base is flat to slightly curved. Aperture is circular.
The specimens are well preserved and show a striking resemblance to specimens of Turritella pseudobandogensis Vredenburg, Reference Vredenburg1928, as illustrated by Vredenburg (Reference Vredenburg1928, p. 376, pl. 19, figs. 3–5, 7) and Jain (Reference Jain2014, p. 133, pl. 27, figs. 24, 25, pl. 28, figs. 4–8) and thus are assigned to this species.
Genus Haustator Denys de Montfort, Reference Denys de Montfort1810
Type species
Haustator gallicus Denys de Montfort, Reference Denys de Montfort1810 (= Turritella imbricataria Lamarck, Reference Lamarck1804). Eocene, Paris Basin.
Haustator cf. H. tauroperturritus Sacco, Reference Sacco1895
Figure 19. (1, 4, 7) Scanning electron micrographs of apices of Haustator cf. H. tauroperturritus Sacco, Reference Sacco1895 (specimen numbers ISI/dwk/TDA/4/a, b, and c) showing early teleoconch part and well-developed apical sculpture. (2) Magnified view of rectangular area in (1). (5) Magnified view of rectangular area in (4). (8) Magnified view of rectangular area in (7). (3) Line diagram of (2) showing primary spital ribs. (6) Line diagram of (5) showing primary spiral ribs. (9) Line diagram of (8) showing primary spiral ribs. The primary spirals are A, B, C (notation after Allmon, Reference Allmon1996). st = suture. (1, 4) Scale bars = 0.5 mm; (2, 3, 7–9) scales bars = 200 μm; (5, 6) scale bars = 100 μm.
Synonymy list
See Appendix 1.
Materials
Eight hundred seventy-three well-preserved specimens (ISI/dwk/TDA/4/1–873). ISI/dwk/TDA/4/1 is the figured specimen. The specimens are from Bulk 1, Bulk 2, and random collections of Loc. 1 (838 specimens); Bulk 3 and random collections of Loc. 2 (31 specimens); and random collections of Loc. 3 (four specimens) (Fig. 1).
Occurrence
Early Miocene (Burdgalian) of Italy, Iran, and Kutch and Dwarka basins (India).
Remarks
Shell is medium to small, turreted in shape, and has approximately nine whorls. Protoconch is smooth and has two and a half whorls. Maximum height is 20.8 mm, and maximum diameter is 10.63 mm. Pleural angle ranges from 23° to 28°. Suture is adpressed. Shell surface is ornamented by three prominent primary spiral ribs (A, B, and C) with apical sculpture formula C1B2A3 (Fig. 19). Approximately two secondary spiral ribs occur at the adapical part of primary spiral B. At least two to three tertiary spiral ribs present between B and C. The whorl profile is imbricate to straight. Opisthocyrt growth lines are observed in the shell surface. Base of the shell is slightly curved, and aperture is very small and circular.
The apical sculpture formula C1B2A3 is the generic sculpture formula for Haustator Denys de Montfort, Reference Denys de Montfort1810 (Marwick, Reference Marwick1957, p. 154; Allmon, Reference Allmon1996, p. 59). In addition, straight to imbricate whorl profile confirms the assignment of the specimens to Haustator.
The shell surface ornamentation is characterized by a prominent primary spiral rib situated near the lower suture.
The specimens show some resemblance to Haustator tauroperturritus Sacco, Reference Sacco1895 as described in Harzhauser et al. (Reference Harzhauser, Reuter, Piller, Berning, Kroh and Mandic2009, p. 343, fig. 3f) from the Miocene of the Kutch Basin, western India, in terms of medium- to small-sized shell, a prominent primary spiral rib situated near the lower suture, a secondary median rib that is comparatively weaker in strength, a slightly curved base, and a circular aperture. However, the whorl profile, apical angle, number and strength of ribs, and granulated and pitted surface of the Haustator from Kutch do not exactly match with our specimens, which thus cannot be confidently assigned to this species.
Subcohort Hypsogastropoda Ponder and Lindberg, Reference Ponder and Lindberg1997
Superfamily Cingulopsoidea Fretter and Patil, Reference Fretter and Patil1958
Family Eatoniellidae Ponder, Reference Ponder1965
Eatoniellidae gen. indet. sp. indet.
Figure 20. (1) Eatoniellidae gen. indet. sp. indet., specimen number ISI/dwk/TDAG/30/i apertural view. (2–5) Neverita sp., specimen number ISI/dwk/TDA/5/i: (2) apertural view; (3) abapertural view; (4) apical view; (5) basal view. (6–8) ?Barleeia sp.: (6, 7) specimen number ISI/dwk/TDAG/16/i: (6) apertural view; (7) abapertural view. (8) Specimen number ISI/dwk/TDAG/16/ii, abapertural view. (9–12) Rissoina sp.: (9, 10) specimen number ISI/dwk/TDA/19/ii: (9) abapertural view; (10) apertural view; (11, 12) specimen number ISI/dwk/TDA/19/i: (11) abapertural view; (12) apertural view. (1, 6–8) Scale bars = 500 μm; (2–5, 9–12) scale bars = 1 mm.
Materials
Two poorly preserved specimens (ISI/dwk/TDAG/30/i, ii). The specimens were collected from Bulk 2 of Loc. 1 (Fig. 1).
Occurrence
Early Miocene (Burdigalian), Dwarka Basin, Gujarat, India.
Description
Shell minute in size, thin, ovate–conic in shape, with maximum diameter 1.29 mm and maximum height 2.21 mm. Apical angle ranges from 72° to 75°, and pleural angle is between 62° and 65°. One smooth rounded protoconch whorl preserved. Spire is of slightly convex outline. Teleoconch consists of three whorls, which are moderately convex in profile. Suture is impressed. Faintly developed axial lirae observed on the surface of the body whorl whereas no ornamentation is discernible in the rest of the teleoconch whorls. Umbilicus is weakly recognizable and entirely covered by the relatively thick inner lip. The outer lip is thin compared with the inner lip. Shape of the aperture is indiscernible and filled with matrix.
Remarks
The specimens are poorly preserved and characterized by an ovate–conic shell shape, a smooth rounded protoconch, an impressed suture, and a body whorl ornamented with faint axial liras. These features place them within the family Eatoniellidae Ponder, Reference Ponder1965. However, the lack of any diagnostic characters, such as a definitive shell surface ornamentation, prevents assignment to any genus or species.
Superfamily Epitonioidea Berry, Reference Berry1910
Family Epitoniidae Berry, Reference Berry1910
Genus Clathrus Agassiz, Reference Agassiz1837
Type species
Scalaria acuta Sowerby, Reference Sowerby1812, subsequent designation by Brown and Neville (Reference Brown and Neville2015, p. 21). Eocene, British Isles.
Clathrus gajensis (Vredenburg, Reference Vredenburg1928)
Figure 21. (1, 2) Nassarius cf. N. beui Jain, Reference Jain2014, specimen number ISI/dwk/TDA/3/iv: (1) abapertural view; (2) apertural view. (3–6) Nassarius anisi n. sp.: (3, 4) specimen number ISI/dwk/TDA/6/ii: (3) abapertural view; (4) apertural view; (5, 6) specimen number ISI/dwk/TDA/6/i: (5) abapertural view; (6) apertural view. (7–10) Nassaria cf. N. harzhauseri Jain, Reference Jain2014: (7, 8) specimen number ISI/dwk/TDA/8/ii: (7) abapertural view; (8) apertural view; (9, 10) specimen number ISI/dwk/TDA/8/i: (9) abapertural view; (10) apertural view. (11, 12) Clathrus gajensis (Vredenburg, Reference Vredenburg1928), specimen number ISI/dwk/TDAG/11/i: (11) abapertural view; (12) apertural view. (13, 14) Dermomurex sp., specimen number ISI/dwk/TDA/9/ii: (13) abapertural view; (14) apertural view. Scale bars = 5 mm.
Synonymy list
See Appendix 1.
Hypotype
Specimen number ISI/dwk/TDAG/11/i. Nandana Shale–Siltstone Unit, Nandana Member, Gaj Formation, Dwarka Basin, India, early Miocene (Burdigalian).
Materials
Five very well-preserved specimens (ISI/dwk/TDAG/11/i–v). ISI/dwk/TDAG/11/i is the figured specimen. The specimens are collected from Bulk 1 (four specimens) and Bulk 2 (one specimen) of Loc. 1 (Fig. 1).
Occurrence
Early Miocene of Kutch and Dwarka basins, India.
Remarks
Shell is small, thin, tall, and slender, turreted in shape, with maximum height 8.49 mm and maximum diameter 4.23 mm. Apical angle is 35°, and pleural angle is 27°. Protoconch is not preserved. The teleoconch comprises at least six convex whorls separated by deeply impressed sutures. Body whorl ornamented by 19–20 sharp, straight to prosocline regularly spaced axial costae. The anterior periphery of the body whorl marked by a sharp, slightly keeled spiral thread that delimits the body whorl from the smooth weakly concave base. Shell is anomphalous. Aperture is axially elliptical to rounded and slightly protruding at the posterior end. The specimens show striking similarity in terms of overall shell outline, outer face features of the whorl, nature of the suture, ornamentation, and shape of the aperture with the holotype of Clathrus gajensis (Vredenburg, Reference Vredenburg1928), as described and illustrated by Vredenburg (Reference Vredenburg1928, pl. 20, fig. 14, pl. 21, fig. 9) and thus are assigned to this species.
Clathrus gajensis differs from the early Miocene species from Karnabrunn (Austria), Korneuburg Basin, Clathrus corrugatus Harzhauser and Landau, Reference Harzhauser and Landau2025 (Harzhauser and Landau, Reference Harzhauser and Landau2025, p. 54, figs, 15K, 17A1, A2) mainly in terms of size, whorl profile, shell surface ornamentation, and aperture. C. corrugatus is large, early teleoconch whorls are convex but the later whorls are gradate-subcylindrical with moderate subsutural shelf, and shell surface is sculptured by 10–12 broad, prosocline, widely spaced, slightly lamellose varices.
Superfamily Naticoidea Guilding, Reference Guilding1834
Family Naticidae Guilding, Reference Guilding1834
Subfamily Polinicinae Gray, Reference Gray1847
Genus Neverita Risso, Reference Risso1826
Type species
Neverita josephinia Risso, Reference Risso1826 (type by monotypy), Recent, Mediterranean Sea.
Neverita sp.
Materials
Seven poorly preserved specimens (ISI/dwk/TDAG/5/i–vii). Shell preserved in all the specimens. The specimens were collected from Bulk 1 (four specimens) and Bulk 2 (three specimens) of Loc. 1 (Fig. 1).
Occurrence
Early Miocene (Burdigalian), Dwarka Basin, Gujarat, India.
Description
Shell thin, minute in size, globose naticiform in shape, phaneromphalous. Shell has approximately three whorls. Protoconch is smooth, paucispiral, and has about one and a half whorls. Maximum height is 5.64 mm, and maximum diameter is 7.62 mm. Pleural angle ranges from 100° to 104°. Spire very low with convex whorls. Suture is adpressed. Shell surface sculptured by very fine spiral liras below the middle of the shell along with closely spaced transverse prosocyrt growth lines. Anterior of the shell is slightly convex and sculptured by very fine angular spiral threads. Umbilicus entirely covered by umbilical callus. Parietal callus thin and partly covers the posterior of the aperture. Ornamentation on the callus indiscernible. Basal lip moderately thick compared with the outer lip. Aperture is subcircular.
Remarks
The specimens studied here are characterized by globose shell shape, a very low spire, and a massive umbilicus callus, which are diagnostic for Neverita Risso, Reference Risso1826 (Majima, Reference Majima1989) and thus are assigned to this genus. However, a poor preservation limits assignment to any species. Neverita sp. is similar to Neverita eocenica (Nagao, Reference Nagao1928) reported from the Eocene of Japan (Majima, Reference Majima1989, p. 49, pl. 4, figs. 13–15) in terms of overall shell outline and shell surface ornamentation. However, Neverita sp. is significantly smaller than N. eocenica. While N. eocenica has a comparatively higher spire, flattened whorls, and a narrowly open umbilicus, N. sp. features a very low spire, convex whorls, and an umbilicus entirely covered by the umbilical callus.
Neverita sp. differs from the Miocene species of Florida, Neverita chipolanus (Dall, Reference Dall1892) (Gardner, Reference Gardner1947, p. 551, pl. 59, fig. 22) mainly in terms of size, number of whorls, shape of aperture, and umbilical features. Neverita chipolanus is moderately large with four whorls, ovate aperture, and umbilical region partially filled by thickly callused parietal wall.
“Rissoiform Clade”
Superfamily Rissooidea Gray, Reference Gray1847
Family Barleeiidae Gray, Reference Gray1857
Genus Barleeia Clark, Reference Clark1853
Type species
Turbo ruber Adams, Reference Adams1797 (= T. unifasciatus Montagu, Reference Montagu1803) (type by monotypy). Recent, eastern Atlantic and Mediterranean Sea.
? Barleeia sp.
Materials
Five poorly preserved specimens (ISI/dwk/TDAG/16/i–v). All the specimens have their shells preserved. ISI/dwk/TDAG/16/i, ii are the figured specimens. The specimens are collected from Bulk 1 collection of Loc. 1 (Fig. 1).
Occurrence
Early Miocene (Burdigalian), Dwarka Basin, Gujarat, India.
Remarks
The shell is thin, very small, and ovate–conic in shape with shell height 3.10 mm and shell diameter 2.28 mm. Overall shell is slightly globular with apical angle 53°–55° and pleural angle 50°–51°. Spire is elevated, and the body whorl is inflated. Protoconch is missing. Four to five whorls preserved. Suture is moderately impressed. The subsutural ramp is flat to slightly convex, gradually becoming convex at the flanks in all the whorls. Shell surface is smooth. Shell is anomphalous. Aperture is elliptical with apertural height 1.27 mm and apertural width 0.87 mm and a thick and narrow anterior inner lip.
Characters such as a minute ovate–conic form, an elevated spire, a non-umbilicate smooth shell, and an elliptical aperture with a narrow anterior inner lip resemble those of Barleeia Clark, 1853, and the specimens are thus temporarily assigned to this genus. However, poor preservation limits the ability to define any diagnostic characters for a species assignment.
Family Rissoinidae Stimpson, Reference Stimpson1865
Genus Rissoina d’Orbigny, Reference d’Orbigny1840
Type species
Rissoina inca d’Orbigny, Reference d’Orbigny1840 (type by original designation), Recent, Eastern Pacific.
Rissoina sp.
Materials
Thirty-three poorly to moderately well-preserved specimens (ISI/dwk/TDAG/19/i–xxxii; ISI/dwk/TDAG/21/i). All specimens have their shells preserved. The specimens are collected from Bulk 1 (23 specimens) and Bulk 2 (10 specimens) of Loc. 1 (Fig. 1).
Occurrence
Early Miocene (Burdigalian), India and Pakistan.
Description
Shell small, turreted in shape, anomphalous. Shell has approximately five whorls. Protoconch is not preserved. Maximum height is 7.70 mm, and maximum diameter is 2.58 mm. Pleural angle ranges from 32° to 35°. Whorls are flat to slightly convex. Suture is impressed. Shell surface ornamented by equally spaced opisthocline axial ribs. The anterior of the body whorl characterized by a prominent spiral thread that demarcates the body whorl from the base of the shell. The anterior of the shell sculptured by very fine spiral threads. Aperture is elliptical in shape.
Remarks
The preservation of the specimens is not sufficiently good for the confident assignment to any species. The overall shell outline, flat to slightly convex whorls, and presence of opisthocline axial ribs show close resemblance to the specimens of Rissoina aff. R. costulata (Dunker, Reference Dunker1860) reported from Quilon (Harzhauser, Reference Harzhauser2014, p. 101, pl. 6, fig. 3; species assigned as nomen dubium in Faber and Gori, Reference Faber and Gori2016). However, the shell sculpture notably differs, with the axial ribs quite wider in thickness in Rissoina sp. compared with the Quilon species. Rissoina sp. differs from the type species, Rissoina inca d’Orbigny, Reference d’Orbigny1840 (p. 395, pl. 53, figs. 11–16), in terms of shell surface ornamentation, whorl profile, and shape of the aperture. Rissoina inca has finely striated axial ornamentation in the early whorls followed by raised spaced ribs in the later whorls, non-convex whorl profile, and semi-lunar aperture.
Superfamily Truncatelloidea Gray, Reference Gray1840
Family Tornidae Sacco, Reference Sacco1896 (1884)
Tornidae gen. indet. sp. indet.
Figure 22. (1–4) Cyclostremiscus sp., specimen number ISI/dwk/TDA/49/i: (1) abapertural view; (2) apertural view; (3) apical view; (4) basal view. (5–7) Tornidae gen. indet. sp. indet., specimen number ISI/dwk/TDA/12/i: (5) abapertural view; (6) apertural view; (7) apical view. (8) Cypraeidae gen indet. sp. indet., specimen number ISI/dwk/TDA/32/I, apertural view. (9–11) Varicospira aff. V. subrimosa (d’Orbigny, Reference d’Orbigny1852): (9) specimen number ISI/dwk/TDA/39, abapertural view; (10, 11) specimen number ISI/dwk/TDA/28/ii: (10) abapertural view; (11) apertural view. (12, 13) Sassia sp., specimen number ISI/dwk/TDA/43/i: (12) abapertural view; (13) apertural view. (1–4, 8) Scale bars = 1 mm; (5–7, 9–13) scale bars = 500 μm.
Materials
Two very poorly preserved specimens (specimen number ISI/dwk/TDAG/12/i, ii). Both specimens have their shell preserved. The specimens were collected from Bulk 1 (one specimen) and Bulk 2 (one specimen) of Loc. 1 (Fig. 1).
Occurrence
Early Miocene (Burdigalian), Quilon and Dwarka basins, India.
Description
Shell moderately thick, small, disc-shaped, phaneromphalous. Shell broader than high (maximum height = 3.23 mm; maximum diameter = 5.38 mm). The body whorl mostly envelopes the spire whorls with only a small portion of the earlier whorls visible. Protoconch is indiscernible. The body whorl gradually expands in width, and a slightly angular spiral thread is visible below the middle of the shell. Shell surface ornamentation is not discernible. Umbilicus is very narrow and almost covered by the umbilical callus. Aperture is circular to subcircular.
Remarks
The specimens are very poorly preserved and show some resemblance to the holotype of Teinostoma mandici Harzhauser, Reference Harzhauser2014 (Harzhauser, Reference Harzhauser2014, p. 101–102, pl. 7, figs. 14–16). The specimens exhibit similarities in overall disc-shaped shell, spire whorls mostly enveloped by the body whorl, a gradually increasing width of body whorl, a mostly covered umbilicus with umbilical callus, and a circular aperture, which securely places the specimens under family Tornidae Sacco, Reference Sacco1896. However, poor preservation of the specimens restricts their further assignment to any genus or species.
Genus Cyclostremiscus Pilsbry and Olsson, Reference Pilsbry and Olsson1945
Type species
Cyclostremiscus panamensis (Adams, Reference Adams1852) (type by original designation); Recent, Panama.
Cyclostremiscus sp.
Materials
One well-preserved specimen (ISI/dwk/TDAG/49/i), shell preserved. ISI/dwk/TDAG/30/i is the figured specimen. The specimen was collected from Bulk 3 of Loc. 2 (Fig. 1).
Occurrence
Early Miocene (Burdigalian), Dwarka Basin, Gujarat, India.
Description
Shell is small, discoidal–turbiniform in shape, phaneromphalous. Shell much wider than high, with shell height 2.68 mm and shell diameter 5.95 mm. Pleural angle is 137°. Shell has three whorls with whorl outline convex and suture deep and incised. Shell surface ornamentation mostly indiscernible with a faint signature of a median carina visible. Base of the shell is flat to slightly convex. Umbilicus wide, with umbilical width 2.40 mm. Aperture is circular.
Remarks
Small size, overall discoidal shell outline, convex whorls, presence of a median carina, wide umbilicus, slightly convex base, and circular aperture securely place the specimen in the genus Cyclostremiscus Pilsbry and Olsson, Reference Pilsbry and Olsson1945. However, the shell lacks diagnostic features necessary for assignment to a new species.
Although very similar in overall morphological features, Cyclostremiscus sp. differs from the type species, Cyclostremiscus panamensis (Adams, Reference Adams1852) (Adams, Reference Adams1852, p. 410), in having an orbicular aperture, deep and narrow umbilicus, and whorls convex above and concave below the middle.
Superorder Latrogastropoda Reidel, Reference Riedel2000
Superfamily Cypraeoidea Rafinesque, Reference Rafinesque1815
Family Cypraeidae Rafinesque, Reference Rafinesque1815
Cypraeidae gen. indet. sp. indet.
Materials
Two very poorly preserved specimens (ISI/dwk/TDAG/32/I, ii), both internal molds. The specimens were collected from Bulk 2 of Loc. 1 (Fig. 1).
Occurrence
Early Miocene (Burdigalian) of Dwarka, India.
Remarks
The specimens are very small, ovate in shape, with the last whorl entirely enveloping the spire whorls. The dorsum is moderately rounded, and the shell surface is smooth. The aperture is narrow, straight to slightly curved to the left. The posterior outlet is obsolete, while the anterior outlet is moderately wide and shallow. Because of these features, the specimens are temporarily assigned to the family Cypraeidae Rafinesque, Reference Rafinesque1815.
Family Rostellariidae Gabb, Reference Gabb1868
Subfamily Rimellinae Stewart, Reference Stewart1926
Genus Varicospira Eames, Reference Eames1952
Type species
Varicospira cancellata (Lamarck, Reference Lamarck1816) (type by subsequent designation), Recent, Indo–Pacific.
Varicospira aff. V. subrimosa (d’Orbigny, Reference d’Orbigny1852)
Synonymy list
See Appendix 1.
Materials
Three very poorly preserved specimens (ISI/dwk/Nm/TDAG/39/i–iii), shell preserved. The specimens were collected from Bulk 1 of Loc. 1 (Fig. 1).
Occurrence
Early Miocene (Burdigalian) of Kutch, Dwarka, Quilon, Assam, and Meghalaya basins, India.
Description
Shell very small (H = 4.61 mm and D = 2.70 mm), fusiform. Shell cyrtoconic with apical angle 59° and pleural angle 55°. Shell has approximately four whorls; protoconch not preserved. Whorls are convex in outline; suture is shallow and adpressed. Ornamentation of the teleoconch whorls is indiscernible. The body whorl is characterized by cancellated ornamentation showing 11 sharp axial costae crosscutting four wavy spiral threads, resulting in a beaded appearance on the axial elements. The anterior of the shell is characterized by a short siphonal canal with a narrow siphonal notch. Aperture is not properly preserved.
Remarks
The specimens show some resemblance to Varicospira subrimosa (d’Orbigny, Reference d’Orbigny1852), as described by Kulkarni et al. (Reference Kulkarni, Kapoor and Borkar2010, p. 321–322, fig. 2m), particularly in terms of cancellated ornamentation, overall shell form, and anterior features of the shell. However, poor preservation hinders a confident assignment of the specimens to Varicospira subrimosa.
Superfamily Tonnoidea Suter, Reference Suter1913
Family Cymatiidae Iredale, Reference Iredale1913
Genus Sassia Bellardi, Reference Bellardi, Cephalopoda and Pteropoda1873
Type species
Sassia apenninica (Sasso, Reference Sasso1827) (type by subsequent designation); Miocene, Tethyan Region.
Sassia sp.
Materials
Five poorly preserved specimens (ISI/dwk/TDAG/43/i–iv, ISI/dwk/TDAG/48/i). All the specimens have their shells preserved. The specimens were collected from Bulk 1 (four specimens) of Loc. 1 and Bulk 3 (one specimen) of Loc. 2 (Fig. 1).
Occurrence
Early Miocene (Burdigalian), Dwarka Basin, Gujarat, India.
Description
Shell very moderately thick, small, fusiform in shape, and anomphalous. Shell higher than broad (maximum height = 3.49 mm; maximum diameter = 1.69 mm). Pleural angle ranges from 39° to 43°. Shell has five whorls. Protoconch is smooth and has approximately one convex mamillated whorl preserved. Whorls are flat to slightly convex in profile with adpressed suture. Shell surface ornamentation barely visible, with some faintly beaded axial threads seen at some places on the body whorl crossed by some spiral threads. The spiral ornamental elements are prominent near the periphery of the aperture. The anterior of the shell is characterized by a very narrow siphonal notch. Columellar lip is moderately thick and folded. Aperture is elliptical in shape with outer lip moderately thick and slightly corrugated whereas the inner lip is comparatively thin.
Remarks
The specimens are poorly preserved with shell intact and characterized by a fusiform shell with convex, mamillated, and smooth whorls. The whorls are flat in profile with an adpressed suture and an elliptical aperture and thus are assigned to Sassia Bellardi, Reference Bellardi, Cephalopoda and Pteropoda1873. The specimens show some resemblance to Sassia (Cymatiella) fennemai (Martin, Reference Martin1899), as described by Reich et al. (Reference Reich, Wesselingh and Renema2014, p. 36, pl. 9, figs. 5, 6), particularly in terms of shell shape and shell surface ornamentation, which includes both axial and spiral elements. However, the shell surface ornamentation of our specimens is barely preserved and lacks the prominent varices and carinas seen in Sassia (Cymatiella) fennemai.
Order Neogastropoda Wenz, Reference Wenz and Schindewolf1938
Superfamily Buccinoidea Rafinesque, Reference Rafinesque1815
Family Nassariidae Iredale, Reference Iredale1916
Subfamily Nassariinae Iredale, Reference Iredale1916
Genus Nassarius Duméril, Reference Duméril1805
Type species
Nassarius (Nassarius) arcularius Linnaeus, Reference Linnaeus1758; Recent, Indo–West Pacific.
Nassarius cf. N. beui Jain, Reference Jain2014
Synonymy list
See Appendix 1.
Materials
Sixty-four moderately well-preserved specimens (ISI/dwk/TDAG/3/i–lv; ISI/dwk/TDAG/7/i–ix). All the specimens are intact and have their shells preserved. The specimens are collected from Bulk 1 (41 specimens) and Bulk 2 (17 specimens) of Loc. 1 and Bulk 3 (four specimens) and random collections (two specimens) of Loc. 2 (Fig. 1).
Occurrence
Early Miocene of Dwarka Basin, India.
Description
Shell moderately thick, small, globular–fusiform in shape, anomphalous. Maximum shell height is 16.99 mm, and maximum shell diameter is 11.61 mm. Apical angle ranges from 64° to 66°. Shell has approximately six whorls. Protoconch is preserved and has two smooth convex whorls. The spire is conical and elevated. Spire whorls are slightly convex in outline. Suture is adpressed. The body whorl is well rounded. Shell surface of the body whorl ornamented by approximately 20 axial ridges, which are crossed by closely spaced spiral threads of weaker strength. Anterior of the body whorl ornamented with about 10 spiral threads of which the first two are the most prominent. Callus well developed at the parietal and inner lip. Aperture is small, narrow, semicircular to elliptical in shape.
Remarks
The specimens are moderately well preserved and characterized by a fusiform shell shape, a conical spire, and a body whorl surface ornamented with approximately 20 axial ribs crossed by fine, closely spaced spirals. The base of the shell is sculptured with about 10 spiral threads, and the aperture is semicircular. These features show similarity to Nassarius beui Jain (Reference Jain2014) (Jain, Reference Jain2014, p. 178–179, pl. 35, figs. 8, 9). However, the lack of well-preserved diagnostic characters in our specimens hinders confident assignment to this species.
Nassarius anisi new species
Holotype
Specimen number ISI/dwk/TDAG/06/i. Nandana Shale–Siltstone Unit, Nandana Member, Gaj Formation, Dwarka Basin, India, early Miocene (Burdigalian).
Materials
Ten moderately well-preserved specimens (ISI/dwk/TDAG/06/i–x). All specimens have their shells preserved. The specimens are from Bulk 2 (two specimens) and random collections (seven specimens) of Loc. 1 and Bulk 3 (one specimen) of Loc. 2 (Fig. 1).
Diagnosis
Whorls flat in outline, shallow adpressed suture, last three whorls have narrow keeled shoulder, body whorl surface sculptured by 22 opisthocyrt axial costae, and anterior of the shell has 10 spiral threads on the thick columellar lip.
Occurrence
Early Miocene (Burdigalian), Dwarka Basin, Gujarat, India.
Description
Shell thick, medium in size, bucciniform in shape, and anomphalous. Maximum shell height is 23.59 mm, and maximum diameter is 13.04 mm. Pleural angle ranges from 50° to 54°. Shell has approximately six whorls. Protoconch preserved with two smooth paucispiral whorls. Whorls are overall flat to slightly convex with shallow adpressed suture. The last three teleoconch whorls have narrow, elevated, keeled, round-topped shoulder. Shell surface ornamented by approximately 22 equally distant opisthocyrt axial costae. Anterior of the shell characterized by short, narrow siphonal canal and prominent columellar lip, which is ornamented by about 10 strong, closely spaced spiral threads. Aperture is ovate to elliptical, with moderately thick outer lip and very thick inner lip. Apertural height is 11.78 mm, and apertural width is 8.07 mm.
Etymology
Named in honor of Indian paleontologist Prof. Anis Kumar Ray.
Remarks
Nassarius anisi n. sp. can be differentiated from Nassarius bhatiyaensis Jain, Reference Jain2014 (Jain, Reference Jain2014, p. 178, pl. 35, figs. 3–7, 10) primarily by shell surface sculpture. N. bhatiyanesis features earlier whorls with rounded axial costae and later whorls with straight axial costae. By contrast, N. anisi exhibits opisthocyrt axial costae throughout ontogeny. In addition, N. bhatiyaensis has an impressed suture with well-rounded whorls, while N. anisi is characterized by a shallow adpressed suture with flat to slightly convex whorls.
Nassarius anisi also can be distinguished from Nassarius beui Jain, Reference Jain2014 (Jain, Reference Jain2014, p. 178–179, pl. 35, figs. 8, 9) by its shell surface ornamentation. N. beui has a shell characterized by axial ribs crossed by fine spiral threads on well-rounded whorls, whereas N. anisi features only axial costae with flat to slightly convex whorls. In addition, N. anisi has a prominent narrow elevated keeled shoulder, which is absent in N. beui.
Nassarius anisi differs from the Miocene species from Kutch Basin, western India, Nassarius kachhensis (Vredenburg, Reference Vredenburg1925) (Vredenburg, Reference Vredenburg1925, p. 210–211, pl. 7, fig. 8) in terms of number of whorls, whorl profile, type of suture, shell surface ornamentation, and features of the aperture. N. kachhensis has of three convex spire whorls with whorls slightly angulated not far from their posterior side. The suture is impressed, and the shell surface is ornamented by 10 axial ribs, which increase to 14 in the body whorl. These axial ribs are subangular, narrowly spaced, slightly curved to oblique, and steeply inclined to the posterior suture. In addition, the axial ornamentation elements are crossed by four spiral threads.
Subfamily Tomliniinae Kantor, Fedosov, Kosyan, Puillandre, Sorokin, Kano, Clark, and Bouchet, Reference Kantor, Fedosov, Kosyan, Puillandre, Sorokin, Kano, Clark and Bouchet2022
Genus Nassaria Link, Reference Link1807
Type species
Nassaria (Nassaria) pusilla Röding, Reference Röding1798, Recent, Southeast Asia.
Nassaria cf. N. harzhauseri Jain, Reference Jain2014
Synonymy list
See Appendix 1.
Materials
Nine poorly preserved specimens (ISI/dwk/TDAG/8/i–ix). All the specimens have their shells preserved. The specimens were collected from Bulk 1 (seven specimens) and Bulk 2 (one specimen) of Loc. 1 and Bulk 3 (one specimen) of Loc. 2 (Fig. 1).
Occurrence
Early Miocene (Burdigalian), Dwarka Basin, Gujarat, India.
Description
Shell small to medium in size, bucciniform in shape, anomphalous. Shell has approximately five whorls, protoconch preserved and characterized by one and a half smooth paucispiral whorls. Maximum height is 11.48 mm, and maximum diameter is 6.27 mm. Pleural angle ranges from 50° to 53°. Spire is moderately slender and is two-fifths of the total height of the shell. Whorls are well rounded in outline, with deep impressed suture. Shell surface of the body whorl ornamented by six to seven spiral threads, which are crosscut by approximately 16–17 widely spaced orthocline axial ribs forming beaded granulations at their intersection. Thick varices appear after exactly half volution growth of the shell. Anterior of the shell has a short siphonal canal. Aperture is mostly indiscernible but appears elliptical in shape.
Remarks
The specimens show some resemblance to Nassaria harzhauseri Jain, Reference Jain2014 (Jain, Reference Jain2014, p. 174–175, pl. 34, figs. 10–14, pl. 42, figs. 8, 10, 11). They are similar in terms of overall shell shape, well-rounded whorls, deep impressed suture, and body whorl ornamentation, which includes six to seven spiral threads crossed by 16–17 axial ribs that form beaded granulation at their intersections. In addition, the anterior features a short siphonal canal although the aperture is indiscernible. However, due to poor preservation of the specimens, confident assignment to any species cannot be done.
Superfamily Muricoidea Rafinesque, Reference Rafinesque1815
Family Muricidae Rafinesque, Reference Rafinesque1815
Subfamily Aspellinae Keen, Reference Keen1971
Genus Dermomurex di Monterosato, Reference di Monterosato1890
Type species
Dermomurex scalaroides (de Blainville, Reference de Blainville1829) (type by typification of replaced name), Recent, Mediterranean Sea.
Dermomurex sp.
Materials
Six poorly preserved specimens (ISI/dwk/TDAG/9/i–iv; ISI/dwk/TDAG/44/I, ii) with partially preserved shell. The specimens were collected from Bulk 1 (two specimens) and Bulk 2 (four specimen) of Loc. 1 (Fig. 1).
Occurrence
Early Miocene (Burdigalian), Dwarka Basin, Gujarat, India.
Description
Shell moderately thick, small, biconical in shape, and anomphalous. Shell has approximately six whorls. Protoconch has only one smooth paucispiral whorl preserved. Maximum height is 11.89 mm, and maximum diameter is 6.72 mm. Pleural angle ranges from 58° to 61°. Whorls are slightly convex with impressed suture. Body whorl sculptured by approximately six to10 axial varices, which are quite prominent in strength in the later part. The varices are crossed by some faintly visible spiral threads. Anterior of the shell characterized by a moderately long siphonal canal, which is distally recurved. Aperture is narrow and elliptical in shape.
Remarks
The specimens are characterized by a biconical shell shape, ornamented with six to 10 opisthocline axial varices crossed by faintly visible spiral threads. The whorls are slightly convex with an impressed suture and a moderately long siphonal canal at the anterior that is distally recurved. These characteristics resemble Dermomurex (Viator) teschlernicolae Harzhauser, Reference Harzhauser2014 (Harzhauser, Reference Harzhauser2014, p. 39–40, pl. 8, figs. 13–15). However, poor preservation hinders a confident assignment to any species.
Superfamily Mitroidea Swainson, Reference Swainson1831
Family Mitridae Swainson, Reference Swainson1831
Mitridae gen. indet. sp. indet.
Materials
Two very poorly preserved specimens (ISI/dwk/TDAG/17/I, ii) with shell preserved. The specimens were collected from Bulk 1 of Loc. 1 (Fig. 1).
Occurrence
Early Miocene (Burdigalian), Dwarka Basin, Gujarat, India.
Remarks
Shell very small, thin, fusiform, and anomphalous. Shell has approximately three whorls. Protoconch is indiscernible. Maximum shell height is 7.98 mm, and maximum width is 4.56 mm. Pleural angle is 54°. Spire whorls are flat in outline with adpressed suture. The body whorl is three-fifths of the total shell height and has a prominent elevated convex shoulder. Shell surface ornamentation is not discernible. The anterior of the shell is slightly slender and is characterized by a very short, narrow siphonal canal. Aperture is very narrow and rounded quadrangular in shape.
The specimens show similarity with the family Mitridae Swainson, Reference Swainson1831 in overall shell shape, whorl outline, narrow aperture, and anterior features of the shell. However, the poor preservation, particularly the indiscernible shell surface ornamentation, hinders their assignment to any genus or species.
Superfamily Olivoidea Latreille, Reference Latreille1825
Family Ancillariidae Swainson, Reference Swainson1840
Genus Alocospira Cossmann, Reference Cossmann1899
Materials
Twelve poorly preserved specimens (ISI/dwk/TDAG/29/i–xii) with shell preserved. The specimens were collected from Bulk 1 (five specimens) and Bulk 2 (six specimen) of Loc. 1 and Bulk 3 (one specimen) of Loc. 2 (Fig. 1).
Occurrence
Early Miocene (Burdigalian), Dwarka Basin, Gujarat, India.
Description
Shell is small, spindle-shaped, with acute apex. Protoconch is small bulbous consisting of approximately one whorl preserved. Spire is calloused with suture between the body whorl and the penultimate whorl visible, being covered by thin callus. The shell surface appears smooth. Columella weakly concave with two columellar plaits visible. Aperture is narrow and semi-elliptical in shape.
Remarks
The specimens are characterized by a small spindle-shaped shell with an acute apex, bulbous protoconch, calloused spire, and a suture visible between body whorl and penultimate whorl, which is covered by a thin callus. The columella is weakly concave with two visible columellar plaits, provisionally placing the specimens in the genus Alocospira Cossmann, Reference Cossmann1899. The specimens show similarity to the early Miocene specimens of Alocospira uter Harzhauser, Reference Harzhauser2014 from the Quilon Basin (Harzhauser, Reference Harzhauser2014, p. 113–114, pl. 9, figs. 6–9) in overall shell outline, protoconch, and anterior features of the shell. However, the specimens lack the characteristic spiral swellings on the spire whorls seen in A. uter. Therefore, due to poor preservation of the specimens and the absence of distinct diagnostic characters, they cannot be confidently assigned to a new species.
Superfamily Conoidea Fleming, Reference Fleming1822
Family Conidae Fleming, Reference Fleming1822
Genus Conus Linneaus, Reference Linnaeus1758
Type species
Conus marmoreus Linnaeus, Reference Linnaeus1758 (type by subsequent designation in Children, Reference Children1823).
Conus sp.
Materials
One poorly preserved specimen (ISI/dwk/Nm/13/12), internal mold. The specimen is from collections of Loc. 3 (Fig. 1).
Occurrence
Miocene of the Dwarka Basin (India).
Remarks
The shell is small, obconical in shape, and anomphalous, consisting of approximately five whorls. The protoconch is not preserved. The maximum width of the shell is 12.60 mm. The spire is very low to depressed, with body whorl considerably larger, showing significant overlap of the previous whorls. The whorls are overall convex, and the suture is deep and grooved. The shell surface is smooth. The anterior of the shell is broken. The overall shell shape, very low to depressed spire, whorl characters, and grooved suture of the specimen conform to the characteristics of Conus Linneaus, 1758. However, the specimen is a broken internal mold with insufficient preservation of diagnostic features for assignment to any species.
Family Raphitomidae Bellardi, Reference Bellardi1875
Genus Cyrillia Kobelt, Reference Kobelt1905
Type species
Cyrillia linearis (Montagu, Reference Montagu1803) (type by typification of replaced name), Recent, British Isles.
? Cyrillia sp.
Materials
Five poorly preserved specimens (ISI/dwk/TDAG/45/i–v), all with shell preserved. ISI/dwk/TDAG/45/i is the figured specimen. The specimens were collected from Bulk 1 (two specimens) and Bulk 2 (three specimens) of Loc. 1 (Fig. 1).
Occurrence
Dwarka Basin, western India (early Miocene).
Description
Shell small, slender, broadly fusiform in shape with shell height 5.57 mm and shell diameter 2.52 mm. Apical angle is 29°–31° and pleural angle is 33°–35°. Protoconch is missing, and teleoconch consists of six straight-walled whorls forming a slender, tall spire. Whorls are gradated/stepped and ornamented by 12–13 straight, regularly spaced axial ribs. The shoulder is marked by a row of nodules forming at the posterior end of each axial rib. Suture is flushed. Shell is anomphalous. Base is elongated and extended at the anterior by a short siphonal notch. Shape of the aperture is slightly elliptical although inconspicuous in most of the specimens. The outer lip is thick and corrugated.
Remarks
The specimens show some resemblance in overall shell outline, tall spire, axial shell surface ornamentation, and basal features such as the curved short siphonal notch to Cyrillia Kobelt, Reference Kobelt1905 (see Fassio et al., Reference Fassio, Russini, Pusateri, Giannuzzi-Savelli, Høisæter, Puillandre, Modica and Oliverio2019; Landau et al., Reference Landau, Harzhauser and Giannuzzi-Savelli2022). However, the whorl outline of Cyrillia is quite convex compared with the specimens, which are thus tentatively placed in this genus. The preservation of the specimens is too poor for confident assignment to any species.
Subclass Heterobranchia Gray, Reference Gray1840
Infraclass Euthyneura Spengel, Reference Spengel1881
Cohort Tectipleura Schrödl et al., Reference Schrödl, Jörger, Klussmann-Kolb and Wilson2011
Subcohort Euopisthobranchia Jörger et al., Reference Jörger, Stöger, Kano, Fukuda, Knebelsberger and Schrödl2010
Order Cephalaspidea Fischer, Reference Fischer1883
Superfamily Bulloidea Gray, Reference Gray, Smedley, Rose and Rose1827
Family Retusidae Thiele, Reference Thiele1925
Retusidae gen. indet. sp. indet.
Materials
Five poorly preserved specimens (ISI/dwk/TDAG/18/i–v) with shell preserved. The specimens were collected from Bulk 1 of Loc. 1 (Fig. 1).
Occurrence
Early Miocene (Burdigalian) of Dwarka Basin, Gujarat, India.
Description
Shell minute, subcylindrical in shape, with a weak concavity in the central part and the flanks nearly parallel. Maximum height is 3.10 mm, and maximum width is 1.41 mm. Aperture is slightly dilated near the apex and becomes very narrow at the center, followed by wide pyriform in the anterior. The apical umbilicus is deep and wide. Columella is concave, and the inner lip is narrow and thin. Umbilicus is very narrow. Shell surface ornamentation is mostly inconspicuous, but some faint axial threads of varying strength along with some spiral liras are visible in the anterior.
Remarks
The specimens show similarity with the morphology of the family Retusidae Thiele, Reference Thiele1925, characterized by their subcylindrical shape, weak concavity in the central part with nearly parallel flanks, deep and wide apical umbilicus, slit-like umbilical chink, and very narrow aperture centrally located and pyriform in the anterior. However, the poor preservation of the specimens, with mostly inconspicuous shell surface ornamentation, hinders any confident assignment to a specific genus or species.
Results
Taxonomic composition of the gastropod fauna
The Nandana Shale–Siltstone Unit (Nmb) represents a turritelline dominated assemblage (TDA) as described by Allmon (Reference Allmon2007), with turritelline gastropods making up 96% of the total gastropod community (Fig. 4). The unit shows a remarkable diversity of 42 gastropod species (see Table 1). The turritelline gastropods are represented by two genera: Turritella and Haustator. At the species level, the turritelline gastropods display remarkably high diversity, including eight species: Turritella assimilis, Turritella narica, Turritella pseudotethis, Turritella kacchensis, Turritella bhagothorensis, Turritella angulata, Turritella pseudobandogensis, and Haustator cf. H. tauroperturritus. The associated gastropods also exhibit considerable diversity with 34 species, among which Nassarius cf. N. beui, Rissoina sp., Vicarya cf. V. verneuili, Scaliola subbella, and Ptychopotamides sp. are the most abundant (Table 1).
Ecological diversity
The Nandana Shale–Siltstone Unit (Nmb) reveals the occupation of 10 different ecological life modes out of the 48 potential cubes of the Bambachian cube (see Fig. 5). Ecologically, this TDA is dominated by semi-infaunal facultatively moving suspension feeders (SI-FM-SU). Less-frequent life modes include epifaunal actively moving herbivores–grazers (EP-AM-HG) and predatory carnivores (EP-AM-CP). Other rare life modes observed are epifaunal actively moving browsing carnivores (EP-AM-CB), omnivores–grazers (EP-AM-HO), scavengers–predators (EP-AM-SP), epifaunal slow-moving browsing carnivores (EP-SM-CB), scavengers–predators (EP-SM-SP), epifaunal facultatively moving herbivores–grazers (EP-FM-HG), and semi-infaunal actively moving predatory carnivores (SI-AM-CP) (for abbreviations, see Materials and methods; Fig. 5).
Petrographic study and microfossil associations
The silty shale facies are composed of microcrystalline silt-sized particles embedded in a clay-rich matrix. This rock consists predominantly of quartz and calcite particles smaller than ∼60 microns (coarse silt and finer) (Fig. 6.1). Bioclastic grains include common benthic foraminifera such as Lockhartia sp., Miogypsina sp., Operculina sp. Quinqueloculina sp., Ammonia sp. (Fig. 6.3, 6.7). Other foraminiferal groups such as Nodosariids and Milliolids are also present in this section (Fig. 6.5). This facies is particularly rich in green alga Halimeda sp., with flat thallus segments (Fig. 6.2). Some broken gastropod shells are observed within the clay matrix. Petrographic study reveals evidence of a distinct small bed with varying lithologies within this shale unit. The facies consists of poorly to moderately sorted, angular quartz grains scattered in a micritic matrix, made primarily of calcite (Fig. 7.1). In some areas, the matrix is extremely fine-grained, and the quartz grains are monocrystalline (Fig. 7.1). Muscovite and plagioclase feldspar are also present in this section as other subordinate minerals (Fig. 7.5). The skeletal grains are composed predominantly of benthic foraminifera of the Rotalia group, Ammonia sp., and ostracods (Fig. 7.2, 7.3). In addition, several barnacles and fragmented barnacle debris are major biogenic components within these samples (Fig. 7.4). Some fragmented algal remains and organic matter are also well preserved. The orientation of bioclasts does not exhibit any noticeable preference, with random orientation of clasts often observed within this siltstone facies.
Discussion
Paleoenvironment interpretation
Turritelline gastropods are suspension feeders with a high fecundity rate and generally flourish in environments with a high rate of suspended nutrients (Allmon, Reference Allmon2007, Reference Allmon2011). The dominance of suspension feeders usually indicates a high nutrient availability during their deposition. These nutrient-rich environments generally result from ocean upwelling events and/or terrestrial freshwater sediment influx (Allmon and Knight, Reference Allmon and Knight1993; Allmon, Reference Allmon2007; Anderson et al., Reference Anderson, Hendy, Johnson and Allmon2017).
Turritelline-dominated assemblages (TDA) in modern oceans are generally found in cooler high-nutrient, subtidal environments at depths between 10 and 100 meters (see Allmon, Reference Allmon2007, Reference Allmon2011; Anderson et al., Reference Anderson, Hendy, Johnson and Allmon2017). By contrast, fossil TDAs during the Miocene are found mostly in warm, nutrient-rich, siliciclastic shallow-marine environments (Allmon, Reference Allmon2007; Anderson et al., Reference Anderson, Hendy, Johnson and Allmon2017). Global δ18O records of benthic foraminifers reveal ocean warming during the early Miocene (Zachos et al., Reference Zachos, Shackleton, Revenaugh, Pälike and Flower2001). This warming resulted in widespread marine incursions into continental margins, the development of carbonate platforms, and diversified coral reefs (Rossetti et al., Reference Rossetti, Bezerra and Dominguez2013). Marine primary productivity increased due to enhanced organic matter flux on the ocean floors, resulting in moderate to major pulses of ocean upwelling events during the early Miocene in equatorial and mid-latitude waters (Spezzaferri, Reference Spezzaferri1995; Diester-Haass et al., Reference Diester-Haass, Billups and Emeis2011). In the Arabian Sea, these upwelling events, along with an intensified oxygen minimum zone, are linked to a reorganization of the Indian Ocean circulation system and the South Asian Monsoon system during this period (Bialik et al., Reference Bialik, Auer, Ogawa, Kroon, Waldmann and Ohkouchi2020). In addition, high-resolution records of δ¹³C, δ¹⁸O, and reconstructed temperature data from subannual growth bands of Turritella during the early Miocene reveal a significant discharge of freshwater into the northeastern Arabian Ocean (Banerjee and Ghosh, Reference Banerjee and Ghosh2024).
The Nandana Shale–Siltstone Unit (Nmb) of the Nandana Member, Gaj Formation is an early Miocene (Burdigalian) TDA with a lithology consisting of a silty shale facies. Analyses of petrography, grain size, and fossil assemblage data reveal dynamic shifts in sedimentary conditions, leading to the coexistence of characteristics typical of both subtidal and intertidal zones within these units. These fluctuations between subtidal and intertidal environments suggest significant environmental mixing. The median grain size of sediment demonstrates a seaward coarsening trend across the tidal flats, coupled with a transition from coarse sand in the subtidal zone to mud in the supratidal zone. This reflects typical accumulation patterns influenced by the selective sorting effects of wave dynamics and tidal currents within the subtidal and shallow intertidal flat regions (Davis, Reference Davis and Davis1978; Pettijohn et al., Reference Pettijohn, Potter and Siever1987).
Shallow marine shelf conditions support large populations of Rotalia and Miliolids groupings, which commonly thrive in well-oxygenated, nutrient-rich waters (Boudagher-Fadel, Reference Boudaugher-Fadel2018; Chaudhuri et al., Reference Chaudhuri, De, Srivastava, Chattopadhyay and Bhaumik2022). Ammonia usually thrives in shallow shelf environments (Murray, Reference Murray2006; Dupuy et al., Reference Dupuy, Rossignol, Geslin and Pascal2010) and can survive fluctuating temperatures, water salinity, and nutrient input (Schnitker, Reference Schnitker1974; Debenay et al., Reference Debenay, Bénéteau, Zhang, Stouff, Geslin, Redois and Fernandez-Gonzalez1998). Quinqueloculina flourishes in shallow, tropical, well-oxygenated, and warm-temperate seas. However, it shows versatility in adapting to different salinity levels, rendering it an important species for indicating near-shore environments (Bandy and Arnal, Reference Bandy and Arnal1957; Chaudhuri et al., Reference Chaudhuri, De, Srivastava, Chattopadhyay and Bhaumik2022). The coexistence of opportunistic benthic foraminifera Ammonia and Quinqueloculina implies deposition in the intertidal to the subtidal zones of the continental shelf, favored by oxygen-rich conditions and elevated nutrient fluxes (Gupta and Platon, Reference Gupta and Platon2006; Murray, Reference Murray2006; Chaudhuri et al., Reference Chaudhuri, De, Srivastava, Chattopadhyay and Bhaumik2022). The occurrence of larger foraminifera such as Lockhartia sp. and Miogypsina sp. indicates shallow-marine environmental conditions with ambient sunlight (Boudagher-Fadel, Reference Boudaugher-Fadel2018). In addition, Halimeda, a green alga, is commonly found inhabiting tropical, subtidal to lower intertidal zones in wave-affected habitats (Dragastan and Herbig, Reference Dragastan and Herbig2007). The large size of barnacles from the middle siltstone bed indicates deposition in a subtidal to intertidal environment with sufficient nutrient supply for higher growth rates (Menge, Reference Menge2000). The biotic association of larger benthic foraminifera such as Operculina, and Miogypsina, along with algae and other mollusks, signifies a highly nutrient-rich environment prevailed during that time. The X-ray diffraction (XRD) results also indicate that the underlying unit of the Nandana Member is dominated by CaCO₃; with the onset of the TDA bed, siliciclastic peaks become prominent, and the overlying unit transitions back to CaCO₃ dominance with minor SiO₂ peaks (Chaudhuri et al. Reference Chaudhuri, Bose, Chattopadhyay, Das and Bhaumik2025). The siliciclastic enrichment in the TDA bed of the Gaj Formation and the shift toward siliciclastic-rich facies likely indicates intensified terrestrial input, enhancing nutrient delivery in shallow-marine settings. By contrast, fossil TDAs during the Miocene are found mostly in warm, nutrient-rich, siliciclastic shallow-marine environments (Allmon, Reference Allmon2007; Anderson et al., Reference Anderson, Hendy, Johnson and Allmon2017). Such conditions are ideal for suspension-feeding gastropods like Turritella, which thrive in high-nutrient, low-energy environments (Allmon and Knight, Reference Allmon and Knight1993). The microfossil association and petrographic study suggest the deposition of sediments of the Nandana Shale–Siltstone Unit (Nmb) under tropical, warm, nutrient-rich, well-oxygenated conditions in subtidal–intertidal conditions. However, further geochemical, isotopic, and paleotemperature studies on the turritelline shells are needed to determine more robust paleoclimatic conditions and depositional history of the Nandana Shale–Siltstone Unit (Nmb).
Acknowledgments
K.B., S.S.D., and S.C. acknowledge the Indian Statistical Institute, Kolkata, for providing fund and infrastructural facilities. This work was supported by the Indian Statistical Institute (5427D for the Year 2019–2020). K.B. also acknowledges IIT Bombay for providing infrastructural facilities. We acknowledge IISER, Kolkata, for providing infrastructural facilities for studying the micro-gastropod specimens. We acknowledge the Department of Earth Sciences, IIT, Kharagpur, for providing SEM facilities for studying the micro-gastropod specimens. We acknowledge B. Mishra, A. Mondal, and S.P. Mallick for their help in taking SEM images at IIT, Kharagpur. K.B. acknowledges the Department of Earth Sciences, IIT, Bombay, for providing SEM facilities for studying the turritelline specimens. K.B. also thanks S.V. Netrawali for her help in capturing SEM images of the protoconch of the turritelline specimens. S.S.D. and K.B. acknowledge the Reprography and Photography Unit, ISI, Kolkata, and P.P. Halder for their help in photoshop editing of the photographs. We are thankful to S. Vinodbhai for his help in fieldwork and T. Kar for preparation of the thin sections. S.C. acknowledges K. Chattopadhyay for his support in thin-section studies and the Micropaleontology Laboratory, IIT (ISM), Dhanbad, for providing infrastructural facilities. A. Ghosh, a native English speaker, has provided corrections to the English language. We acknowledge W.D. Allmon and an anonymous reviewer for critically reviewing the manuscript and providing valuable corrections and suggestions. We also thank J.O.R. Ebbestad, associate editor, Journal of Paleontology, for his suggestions to the manuscript.
Competing interests
The authors declare no competing interests.
Data availability statement
Data available in Zenodo Digital Repository: https://doi.org/10.5281/zenodo.18624645.
Appendix 1. Synonymy list of identified species from the Nandana Shale–Siltstone Unit, Nandana Member, Gaj Formation, Dwarka Basin, India
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1. Neocollonia aff. N. pseudomunda (Harzhauser, Reference Harzhauser2014):
Reference Harzhauser2014 Bothropoma pseudomunda Harzhauser, p. 81, plate. 1, figs. 8–13.
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2. Globularia cf. G. carlei (Finlay, Reference Finlay1927):
Reference Sowerby1840 Natica callosa; Sowerby, pl. 26, fig. 3; junior primary homonym of Natica callosa Cristofori and Jan, Reference Cristofori and Jan1832.
Reference Noetling1895 non Natica callosa; Noetling, Reference Noetling1895, p. 23, pl. 6, fig. 8.
Reference Noetling1901 non Natica callosa; Noetling, Reference Noetling1901, p. 283, pl. 18, figs. 24, 25, pl. 19, fig. 1.
cf. Reference Finlay1927 Natica carlei Finlay (new name for Natica callosa Sowerby,Reference Sowerby1840 not of Cristofori and Jan), p. 498.
Reference Vredenburg1928 Ampullina (Cernina) callosa; Vredenburg, p. 400.
Reference Cox1930 Cernina callosa; Cox, p. 107, pl. 12, fig. 11.
Reference Dey1961 Globularia (Cernina) carlei; Dey, p. 54, pl. 5, figs. 3, 5.
Reference Harzhauser, Reuter, Piller, Berning, Kroh and Mandic2009 Globularia carlei; Harzhauser et al., p. 348, fig. 2c, d.
Reference Jain2014 Globularia carlei; Jain, p. 140, pl. 32, figs. 11, 12, 15, 16.
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3. Vicarya cf. V. verneuili (d’Archiac, Reference d’Archiac1850):
Reference d’Archiac1850 Nerinea? verneuili d’Archiac, p. 286.
Reference d’Archiac and Haime1854 Vicarya verneuili; d’Archiac and Haime, p. 298, pl. 28, fig. 4a, b.
Reference Vredenburg1928 Telescopium charpentieri; Vredenburg, p. 364, pl. 15, figs. 17, 18; pl. 17, figs. 1, 4, 6–8.
Reference Kanno1986 Vicarya verneuili; Kanno, p. 37 (pars), pl. 1, figs. 1a, b (Pakistani specimen only).
Reference Jain2014 Vicarya verneuili; Jain, p. 129, pl. 28, figs. 30, 31, pl. 38, figs. 18, 19.
Reference Harzhauser, Reuter, Mohtat and Piller2017 Vicarya verneuili; Harzhauser et al., p. 529, fig. 4m.
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4. Scaliola subbela Harzhauser, Reference Harzhauser2014:
Reference Harzhauser2014 Scaliola subbela Harzhauser, p. 89, pl. 3, fig. 13.
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5. Turritella angulata Sowerby, Reference Sowerby1840:
Reference Sowerby1840 Turritella angulata Sowerby, pl. 26, fig. 7.
Reference Dunker1847 Turritella acuticarinata; Dunker, p. 132, pl. 28, fig. 10.
Reference d’Archiac and Haime1854 Turritella angulata; d’Archiac and Haime, p. 294, pl. 27, figs. 6–9.
Reference Jenkins1864 Turritella acuticingulata; Jenkins, p. 58, pl. 7, fig. 1.
Reference Jenkins1864 Turritella simplex; Jenkins, p. 59, pl. 7, fig. 2.
Reference Martin1879–80 Turritella simplex; Martin, p. 67, pl. 11, figs. 10, 11.
Reference Noetling1901 Turritella angulata; Noetling, p. 272, pl. 18, figs. 13–15.
Reference Noetling1901 Turritella simplex; Noetling, p. 273, pl. 18, figs. 1–4.
Reference Martin1905 Turritella djadjariensis; Martin, p. 288, pl. 34, figs. 532–538.
Reference Vredenburg1928 Turritella angulata; Vredenburg, p. 378.
Reference Cox1936 Turritella angulata; Cox, p. 38, pl. 8, figs. 20–24.
Reference Mukherjee1939 Turritella (Torculoidella) angulata; Mukerjee, p. 44, pl. 2, figs. 17–21, pl. 3, figs. 1, 2.
Reference Harzhauser, Reuter, Piller, Berning, Kroh and Mandic2009 Zaria angulata; Harzhauser et al., p. 343, figs. 3a–d.
Reference Kulkarni, Kapoor and Borkar2010 Zaria angulata; Kulkarni et al., p. 314, fig. 2g.
Reference Jain2014 Zaria angulata; Jain, p. 134, pl. 27, figs. 12–19.
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6. Turritella narica Vredenburg, Reference Vredenburg1928:
Reference Vredenburg1928 Turritella narica Vredenburg, p. 375, pl. 18, figs. 13–17, pl. 19, figs. 2, 6.
Reference Vredenburg1928 Turritella narica; Vredenburg var. baluchistanensis Vredenburg, p. 375, pl. 18, figs. 10, 20, 22, 25, pl. 21, fig. 5.
Reference Kulkarni, Kapoor and Borkar2010 Turritella narica; Kulkarni et al., p. 312, fig. 2d, e.
Reference Kulkarni, Kapoor and Borkar2010 Turritella narica; Vredenburg var. baluchistanensis Kulkarni et al., p. 313, fig. 2f.
Reference Jain2014 Turritella narica; Jain, p. 132, pl. 28, figs. 9–17.
Reference Jain2014 Turritella bandogensis; Martin, 1879 Jain, p. 130, pl. 27, figs. 22, 23, pl. 28, figs. 1, 2.
Reference Jain2014 Turritella pseudobandogensis; Vredenburg, Reference Vredenburg1928 Jain, p. 133, pl. 27, figs. 24, 25, pl. 28, figs. 4–8.
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7. Turritella assimilis Sowerby, Reference Sowerby1840:
Reference Sowerby1840 Turritella assimilis Sowerby, explanation of plates (no page number), pl. 26, fig. 8.
Reference Vredenburg1928 Turritella assimilis; Vredenburg, p. 377 (partim).
Reference Harzhauser, Reuter, Piller, Berning, Kroh and Mandic2009 Turritella assimilis; Harzhauser et al., p. 341, fig. 3j–n.
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8. Turritella bhagothorensis Vredenburg, Reference Vredenburg1928:
Reference Vredenburg1928 Turritella bhagothorensis Vredenburg, p. 380, pl. 21, figs. 1, 3, 6, 7.
Reference Jain2014 Turritella bhagothorensis; Jain, p. 131, pl. 27, figs. 26, 27.
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9. Turritella kachhensis Vredenburg, Reference Vredenburg1928:
Reference Vredenburg1928 Turritella heberti kachhensis Vredenburg, p. 381.
Reference Harzhauser, Reuter, Piller, Berning, Kroh and Mandic2009 Turritella kachhensis; Harzhauser et al., p. 341, figs. 3g–i, 5l.
Reference Jain2014 Turritella kachhensis; Jain, p. 132, pl. 27, figs. 20, 21.
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10. Turritella pseudotethis Vredenburg Reference Vredenburg1928:
Reference Vredenburg1928 Turritella pseudotethis Vredenburg, p. 380, pl. 21, figs. 2, 8.
Reference Jain2014 Turritella pseudotethis; Jain, p. 134, pl. 38, fig. 3a, b.
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11. Turritella pseudobandogensis Vredenburg, Reference Vredenburg1928:
Reference Vredenburg1928 Turritella pseudobandogensis Vredenburg, p. 376, pl. 19, figs. 3–5, 7.
Reference Jain2014 Turritella pseudobandogensis; Jain, p. 133, pl. 27, figs. 24, 25; pl. 28, figs. 4–8.
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12. Haustator cf. H. tauroperturritus Sacco, Reference Sacco1895:
Reference Sacco1895 Haustator tauroperturritus Sacco, p. 20, pl. 2, fig. 9.
Reference Harzhauser, Reuter, Piller, Berning, Kroh and Mandic2009 Haustator tauroperturritus; Harzhauser et al., p. 343, fig. 3f.
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13. Clathrus gajensis (Vredenburg, Reference Vredenburg1928):
Reference Vredenburg1928 Scala (Clathrus) gajensis Vredenburg, p. 401, pl. 20, fig. 14, pl. 21, fig. 9.
Reference Kulkarni, Kapoor and Borkar2010 Clathrus gajensis; Kulkarni et al., p. 318, fig. 2k.
Reference Jain2014 Clatharus gajensis; Jain, p. 168, pl. 29, figs. 8, 9; pl. 38, fig. 15; pl. 39, figs. 7, 8.
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14. Varicospira aff. V. subrimosa (d’Orbigny, Reference d’Orbigny1852):
Reference Sowerby1840 Rostellaria rimosa; Sowerby, pl. 26, fig. 17 (junior primary homonym of R. rimosa Brander and Solander, Reference Brander and Solander1766).
Reference d’Orbigny1852 Rostellaria subrimosa d’Orbigny, p. 59 (replacement name for R. rimosa Sowerby, Reference Sowerby1840, not of Brander and Solander, Reference Brander and Solander1766).
Reference Vredenburg1925 Rimella subrimosa; Vredenburg, p. 320, pl. 6, figs. 7–10.
Reference Mukherjee1939 Rimella subrimosa; Mukerjee, p. 49, pl. 3, figs. 21, 22.
Reference Dey1961 Dientomochilus (Varicospira) subrimosa; Dey, p. 67.
Reference Harzhauser, Reuter, Piller, Berning, Kroh and Mandic2009 Varicospira subrimosa; Harzhauser et al., p. 345, fig. 2o, p.
Reference Kulkarni, Kapoor and Borkar2010 Rimella subrimosa; Kulkarni et al., p. 321, fig. 2m.
Reference Jain2014 Varicospira subrimosa; Jain, p. 154, pl. 31, figs. 1, 2.
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15. Nassarius cf. N. beui Jain, Reference Jain2014:
Reference Jain2014 Nassarius beui Jain, p. 178, pl. 35, figs. 8, 9.
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16. Nassaria cf. N. harzhauseri Jain, Reference Jain2014:
Reference Jain2014 Nassaria harzhauseri Jain, p. 174, pl. 34, figs. 10–14, pl. 42, figs. 8, 10, 11.
