Introduction
Physeteroidea is a monophyletic clade within Odontoceti, the toothed whales (Geisler et al., Reference Geisler, McGowen, Yang and Gatesy2011). Physeteroid origins trace back to the late Oligocene, and the diversity of Physeteroidea peaked during the Middle and Late Miocene (Mchedlidze, Reference Mchedlidze1970; Gol’din & Marareskul, Reference Gol’din and Marareskul2013; Lambert et al., Reference Lambert, Bianucci and de Muizon2017; Lambert et al., Reference Lambert, de Muizon, Urbina and Bianucci2020; Paolucci et al., Reference Paolucci, Buono, Fernández, Marx and Cuitiño2020; Peri et al., Reference Peri, Collareta, Aringhieri, Caramella, Foresi and Bianucci2022). The clade comprises three extant species: giant sperm whale (Physeter macrocephalus Linnaeus, Reference Linnaeus1758), pygmy sperm whale (Kogia breviceps (de Blainville, Reference de Blainville1838)) and dwarf sperm whale (Kogia sima (Owen, Reference Owen1866)). All of the extant members are specialized deep-diving suction feeders, preying on cephalopods. The extant sperm whales lack their upper dentition or have vestigial teeth positioned in their maxilla (Werth, Reference Werth2004, Reference Werth2006). Some extinct physeteroids were probably foraging at great depths as well, but the full shift to a deep-diving ecology likely occurred relatively recently (Lambert, Reference Lambert2008). Most of the Miocene representatives of Physeteroidea still possessed upper dentition and displayed a wide variety in feeding strategies. The largest members with teeth up to 36.2 cm in length were mostly macroraptorial, feeding on fish and possibly on medium-sized cetaceans as well (Lambert et al., Reference Lambert, Bianucci, Post, de Muizon, Salas-Gismondi, Urbina and Reumer2010b; Lambert et al., Reference Lambert, Bianucci and de Muizon2017; Reumer et al., Reference Reumer, Mens and Post2017). Recently, Watmore and Prothero (Reference Watmore and Prothero2023) described a 25 cm long macropredatory physeteroid tooth from California. Other extinct physeteroids with smaller teeth (physeterids and kogiids) were mostly piscivorous, fed on benthic prey or predated on cephalopods through suction feeding (Benites-Palomino et al., Reference Benites-Palomino, Vélez-Juarbe, Salas-Gismond and Urbina2020; Collareta et al., Reference Collareta, Lambert, de Muizon, Benites Palomino, Urbina and Bianucci2020; Benites-Palomino et al., Reference Benites-Palomino, Vélez-Juarbe, Collareta, Ochoa, Altamirano, Carré, Laime, Urbina and Salas-Gismondi2021). All physeteroids are characterized by their remarkable skull structure, which makes room for a supracranial basin containing the spermaceti organ, which plays a role in echolocation (Cranford et al., Reference Cranford, Amundin and Norris1996; Paolucci et al., Reference Paolucci, Buono, Fernández, Marx and Cuitiño2020).
The stem physeteroid genus Scaldicetus du Bus, Reference du Bus1867 is mainly based on isolated teeth, which is considered material of limited diagnostic value (Bianucci & Landini, Reference Bianucci and Landini2006; Toscano et al., Reference Toscano, Abad, Ruiz, Muñiz, Álvarez, García and Caro2013; Marra et al., Reference Marra, Carone and Bianucci2016; Lambert et al., Reference Lambert, Bianucci and de Muizon2017; Reumer et al., Reference Reumer, Mens and Post2017; Bosselaers & Van Nieulande, Reference Bosselaers and Van Nieulande2018). However, studies on physeteroid dentition of the last three decades do show characterizing features in size and morphology for different physeteroid species (Hirota & Barnes, Reference Hirota and Barnes1994; Kazár, Reference Kazár2002; Bianucci et al., Reference Bianucci, Landini and Varola2004; Bianucci & Landini, Reference Bianucci and Landini2006; Kimura et al., Reference Kimura, Hasegawa and Barnes2006; Bloodworth & Odell, Reference Bloodworth and Odell2008; Lambert, Reference Lambert2008; Boersma & Pyenson, Reference Boersma and Pyenson2015; Lambert et al., Reference Lambert, Bianucci and de Muizon2017; Collareta et al., Reference Collareta, Fulgosi and Bianucci2019; Benites-Palomino et al., Reference Benites-Palomino, Vélez-Juarbe, Salas-Gismond and Urbina2020; Lambert et al., Reference Lambert, de Muizon, Urbina and Bianucci2020; Kimura & Hasegawa, Reference Kimura and Hasegawa2022; Peri et al., Reference Peri, Collareta, Aringhieri, Caramella, Foresi and Bianucci2022). The genus Scaldicetus was introduced by du Bus (Reference du Bus1867) based on 45 large physeteroid teeth with rugose enamel-capped crowns from the Upper Miocene of Borgerhout, Antwerp, Belgium. Solely based on the dentition du Bus erected the species Scaldicetus caretti. Following this classification, multiple large enamel-capped sperm whale teeth have been assigned to the genus Scaldicetus (Table 2). However, Bianucci & Landini (Reference Bianucci and Landini2006) regarded the genus unutilizable due to the low diagnostic value of isolated physeteroid teeth and they restricted the generic and specific name only to the lectotype of S. caretti (IRSNB M. 512) from Borgerhout. Lambert & Bianucci (Reference Lambert and Bianucci2019) confirmed this conclusion and referred to other isolated physeteroid teeth as Physeteroidea indet. Recently, teeth comparable to the type material of S. caretti that were collected from the Westerschelde estuary, the Netherlands, were tentatively attributed to the genus Zygophyseter Bianucci & Landini, Reference Bianucci and Landini2006 by Reumer et al. (Reference Reumer, Mens and Post2017). Despite the conclusions of Bianucci & Landini (Reference Bianucci and Landini2006), several physeteroid findings from across the globe are still attributed to the unutilized Scaldicetus genus.
Here we report a large, well-preserved isolated physeteroid tooth similar to the teeth of the type material of Scaldicetus caretti (as defined by Bianucci & Landini, Reference Bianucci and Landini2006 and Lambert & Bianucci, Reference Lambert and Bianucci2019) and resembling Zygophyseter varolai (Bianucci & Landini, Reference Bianucci and Landini2006). It was found in Miocene deposits at Liessel, Noord-Brabant province, the Netherlands. We also provide a list of modern classifications of Scaldicetus species/specimens to ensure future adherence to the restrictions set by Bianucci & Landini (Reference Bianucci and Landini2006).
Methods and materials
The Miocene physeteroid tooth from Liessel is in the collection of the Oertijdmuseum in Boxtel (MAB13159). The specimen was impregnated using methyl-methacrylate copolymer dissolved in acetone. Measurements were taken with digital callipers and compared to other physeteroid teeth based on descriptions in the literature.
Systematic palaeontology
Order Cetacea Brisson, Reference Brisson1762
Suborder Odontoceti Flower, Reference Flower1867
Superfamily Physeteroidea Gray, Reference Gray1821
Physeteroidea indet. cf. Scaldicetus caretti
Locality and stratigraphy
MAB13159 was recovered ex situ at Liessel near Eindhoven, Noord-Brabant Province, the Netherlands (Fig. 1). It was dredged by the sand-lime brick factory Hoogdonk and discovered on the sand deposit area. Here terrestrial sediment from the Pleistocene and Pliocene and marine sediment from the Upper Miocene is extracted (Peters, Reference Peters2009; Bisconti et al., Reference Bisconti, Munsterman, Fraaije, Bosselaers and Post2020).
Figure 1. Locality of MAB13159. (A) Map of The Netherlands where the red star indicates the Liessel section. (B) Map of Liessel and surroundings where the red star indicates the exact locality of the discovery: sand-lime brick factory Hoogdonk.
Description
MAB13159 (Fig. 2) is heavily mineralized and has a total length of 227 mm. The tooth is distally curved and thickened, in contrast to the relatively flat mesial side (Fig. 2). The lingual/labial side of an isolated physeteroid tooth cannot be determined. The crown is 41.3 mm long and makes up about 18 per cent of the total tooth length. It has a conical shape with a subcircular cross-section. A small part of the apex of the crown is missing due to erosion. The crown is covered in a thick layer of enamel revealing natural wear with a striped (crenulated) pattern showing longitudinal ridges and grooves of approximately 1 mm in width. The margin of the enamel is irregular, but on the mesial side this margin is well-preserved, giving an indication of the actual base of the crown (Fig. 3). At the base of the crown, the mesiodistal diameter measures 31.7 mm and the labiolingual diameter 32.2 mm. Here the enamel forms a continuous surface with the cement of the root.
Figure 2. Different views of tooth. (A) Lingual or labial view with the gingival collar represented with orange dotted lines, the folding indicated by the white arrow. The white rectangle displays the position of Fig. 3. (B) Distal view with the upper boundary of the gingival collar represented with an orange dotted line. (C) Labial or lingual view. (D) Mesial view.
The robust root has a maximum mesiodistal diameter of 74.2 mm and slightly smaller maximum labiolingual diameter of 67.5 mm. It is subcircular in cross-section throughout the root. The maximum diameter is positioned at about mid-length of the tooth. Approaching the crown, the diameter becomes quickly more slender, with a crown diameter/maximum root diameter ratio of 0.43. A distal view of the root clearly shows the upper boundary of the gingival collar at about 70 mm below the apex of the crown (measured along the curvature of the tooth) (Fig. 2B). Although the lower boundary is much harder to distinguish, it appears to have been located at mid-length of the tooth about 20 mm below the upper boundary (Fig. 2A). Anteriorly, the same gingival boundary runs more diagonally, leading to a folding of the gingival collar (Fig. 2A and B). This corresponds to the occlusion of the opposite teeth, indicating the presence of dentition in both the maxilla and mandible (Bianucci & Landini, Reference Bianucci and Landini2006). However, it is impossible to establish whether the isolated tooth was positioned in the upper or lower jaw. The end of the root is damaged. At the apex of the root, the pulp cavity is present. The pulp cavity has an average diameter of 18.8 mm. This is relatively small and indicates that the tooth belonged to an older individual (Bosselaers & Van Nieulande, Reference Bosselaers and Van Nieulande2018).
Figure 3. Close-up of the mesial side of the crown.
Discussion
MAB13159
The combined presence of several morphological features including the large size of the tooth, the wide and robust root, a thick crenulated enamel cap and the folding of the gingival collar indicates MAB13159 belonged with great certainty to a physeteroid with a macroraptorial feeding strategy (Bianucci & Landini, Reference Bianucci and Landini2006; Gol’din & Marareskul, Reference Gol’din and Marareskul2013; Reumer et al., Reference Reumer, Mens and Post2017; Bosselaers & Van Nieulande, Reference Bosselaers and Van Nieulande2018). According to the most recent phylogenetic analysis of Peri et al. (Reference Peri, Collareta, Aringhieri, Caramella, Foresi and Bianucci2022), the macroraptorial sperm whales are identified as a polyphyletic group comprised of the stem physeteroids Brygmophyseter shigensis (Kimura et al., Reference Kimura, Hasegawa and Barnes2006), Zygophyseter varolai (Bianucci & Landini, Reference Bianucci and Landini2006), Acrophyseter robustus (Lambert et al., Reference Lambert, Bianucci and de Muizon2017), Acrophyseter deinodon (Lambert et al., Reference Lambert, Bianucci and de Muizon2008), Acrophyseter sp. (Lambert et al., Reference Lambert, Bianucci and de Muizon2017) and the crown physeteroid Livyatan melvillei (Lambert et al., Reference Lambert, Bianucci, Post, de Muizon, Salas-Gismondi, Urbina and Reumer2010b). In size and morphology, the lectotype of Scaldicetus caretti is very comparable with the general characteristics of a macroraptorial physeteroid tooth indicating the inclusion of the S. caretti type material in the macroraptorial sperm whales too (Reumer et al., Reference Reumer, Mens and Post2017).
Recently described Dutch discoveries (both from the Westerschelde) include NMR999100010227 and NMR999100010228 identified as cf. Zygophyseter sp. (Reumer et al., Reference Reumer, Mens and Post2017) and the massive tooth described by Bosselaers & Van Nieulande (Reference Bosselaers and Van Nieulande2018) tentatively classified as a Physeteroidea tooth. Other stem physeteroid discoveries from the North Sea area include the Scaldicetus caretti type material (du Bus, Reference du Bus1867), ‘Scaldicetus grandis’ (du Bus, Reference du Bus1872), Eudelphis mortezelensis (du Bus, Reference du Bus1872), Hoplocetus borgerhoutensis (du Bus, Reference du Bus1872) and Hoplocetus ritzi (Hampe, Reference Hampe2006). Following the reasoning of Bianucci & Landini (Reference Bianucci and Landini2006) and Lambert & Bianucci (Reference Lambert and Bianucci2019), the solely tooth-based genus Hoplocetus (Gervais, Reference Gervais1848-Reference Gervais1852) can also be regarded unutilizable. However, a complete revision of Hoplocetus is beyond the scope of this paper.
The sizes of both cf. Zygophyseter sp. teeth (NMR999100010227 and NMR999100010228) are very comparable with MAB13159 (Table 1). NMR999100010228 is heavily damaged, which precludes precise comparisons with MAB13159 (Reumer et al., Reference Reumer, Mens and Post2017: Fig. 2). The largest difference in dimensions between the specimens is present in the crown. The crown of the better preserved anterior positioned NMR999100010227 is smaller in length and diameter. The crown length/total length ratio of the tooth is smaller as well. Although this ratio from MAB13159 is approximately 18 per cent, the crown of NMR999100010227 makes up about 9–16 per cent of the total tooth length. In addition to this, NMR999100010227 has a crown diameter/maximum root diameter ratio of 32 per cent (Reumer et al., Reference Reumer, Mens and Post2017), while MAB13159’s ratio is higher with a ratio of 43 per cent. This means that approaching the crown from the greatest diameter of the tooth NMR999100010227 narrows much more compared to MAB13159. Zygophyseter varolai has a difference in crown length/total length ratio as well (Varola et al., Reference Varola, Landini and Pilleri1988). The anterior Zygophyseter varolai teeth show a ratio of approximately 12 per cent, which is smaller compared to the ratio of MAB13159. In addition to this, the overall size of the Z. varolai teeth is smaller than that of NMR999100010227 and MAB13159, with a mean total tooth length of 176 mm and a maximum mesiodistal diameter of 52 mm (Varola et al., Reference Varola, Landini and Pilleri1988: Table II). The morphology of both NMR999100010227 and Zygophyseter varolai are relatively similar to MAB13159, as well (Varola et al., Reference Varola, Landini and Pilleri1988: pl. 1; Reumer et al., Reference Reumer, Mens and Post2017: Fig. 1). However, some characteristic differences are noteworthy. The anterior teeth of Zygophyseter varolai possess a strong curvature of the external root and both NMR999100010227 and Z. varolai have their largest diameter at two-thirds of the height of the tooth. This differs from MAB13159 which has a relatively straight root with a moderately curved upper part and the largest horizontal extension at mid-height of the tooth. Other than the difference in root curvature and largest diameter, both NMR999100010227 and NMR999100010228 and the anterior teeth of Z. varolai are to some extent similar in size (Table 1) and morphology.
Table 1. Measurements of various physeteroid teeth in millimetres with the size range between brackets
1 Reumer et al. (Reference Reumer, Mens and Post2017).
2 Varola et al. (Reference Varola, Landini and Pilleri1988).
3 Bosselaers & Van Nieulande (Reference Bosselaers and Van Nieulande2018).
4 Based on Table 1 in Lambert & Bianucci (Reference Lambert and Bianucci2019).
5 Based on Figure 16 in Hampe (Reference Hampe2006).
6 Based on the teeth description and Figure 6 in Lambert (Reference Lambert2008).
7 du Bus (Reference du Bus1872).
8 Hampe (Reference Hampe2006).
The massive tooth from the Westerschelde described by Bosselaers & Van Nieulande (Reference Bosselaers and Van Nieulande2018) has not enough distinguishable features due to bioerosion for meaningful comparisons to be made with the present specimen. In size, the tooth is similar to the enormous teeth of Livyatan melvillei from Peru (Lambert et al., Reference Lambert, Bianucci, Post, de Muizon, Salas-Gismondi, Urbina and Reumer2010b). Other fossil stem physeteroid teeth from the North Sea basin like ‘Scaldicetus grandis’ (Abel, Reference Abel1905: Figs. 3 & 4; Hampe, Reference Hampe2006: Fig. 16), Eudelphis mortezelensis (Lambert, Reference Lambert2008: Fig. 6), Hoplocetus ritzi (Hampe, Reference Hampe2006: Figs. 3–5 & Table 1) and Hoplocetus borgerhoutensis (Van Beneden & Gervais, Reference Van Beneden and Gervais1868–Reference Van Beneden and Gervais1879: pl. XX: Fig. 28) are very different in morphology and smaller in size when compared to MAB13159 (Table 1).
Just like NMR999100010227 and NMR999100010228, MAB13159 shows resemblance to Scaldicetus caretti dentition (Reumer et al., Reference Reumer, Mens and Post2017). MAB13159 even seems to be almost identical in size and shape to some teeth of the lectotype of S. caretti (Lambert & Bianucci, Reference Lambert and Bianucci2019: Fig. 1 & Table 1). Aside from Zygophyseter varolai and NMR999100010227, teeth of S. caretti are relatively straight with a moderately curved external root and have their largest diameter at mid-height, just like MAB13159. This indicates MAB13159 could belong to the same species as the Scaldicetus caretti type material. Despite the restrictions of Bianucci & Landini (Reference Bianucci and Landini2006), Scaldicetus caretti is still a valid species with an existing type series. Therefore, we here assign MAB13159 to Physeteroidea indet. cf. Scaldicetus caretti. This indicates probable conspecificity of MAB13159 and the type material of S. caretti, within an undetermined taxonomic unit inside the Physeteroidea. The better preserved NMR999100010227 shows morphological similarity with Zygophyseter varolai and seems justly attributed to Physeteroidea indet. cf. Zygophyseter sp. However, the heavily damaged NMR999100010228 has little comparable features. Therefore, we would cautiously suggest to just refer to NMR999100010228 as Physeteroidea indet. to prevent using Zygophyseter as a wastebasket genus. Overall, the dentition of the type material of S. caretti is quite similar to the teeth of Z. varolai.
Most findings of the superfamily Physeteroidea are of Middle and Late Miocene age. All recorded marine fossils from Liessel originate from Upper Miocene strata (Peters, Reference Peters2009; Jagt et al., Reference Jagt, Fraaije and Van Bakel2009; Bisconti et al., Reference Bisconti, Munsterman, Fraaije, Bosselaers and Post2020; Peters et al., Reference Peters, Munsterman and Post2021). The lectotype of Scaldicetus caretti is considered to be of Tortonian age (early Late Miocene, c. 11.6–7.2 Ma) (Lambert & Bianucci, Reference Lambert and Bianucci2019). The other stem physeteroid Zygophyseter varolai dates back to approximately 10.5–8.14 Ma (Bianucci & Landini, Reference Bianucci and Landini2006). These considerations make a Late Miocene age for MAB13159 likely.
Derived from the vertical root and chipping fractures in the Scaldicetus caretti type material and the estimation of the bite force of Zygophyseter varolai, both sperm whale species probably fed on other marine vertebrates and likely occupied an ecological niche comparable to that of the recent killer whale (Orcinus orca Linnaeus, Reference Linnaeus1758). The thick and crenulated enamel and thick cementum layer of both extinct sperm whales indicate a diet probably even more macroraptorial than that of O. orca (Bianucci & Landini, Reference Bianucci and Landini2006; Toscano et al., Reference Toscano, Abad, Ruiz, Muñiz, Álvarez, García and Caro2013; Lambert & Bianucci, Reference Lambert and Bianucci2019; Peri et al., Reference Peri, Falkingham, Collareta and Bianucci2021).
Some remarks on Scaldicetus species/specimens
Both mentions of the taxonomic restriction of Scaldicetus to the lectotype by Bianucci & Landini (Reference Bianucci and Landini2006) and Lambert & Bianucci (Reference Lambert and Bianucci2019) risking being overlooked, we consider it useful to list the only valid Scaldicetus taxon, the taxa previously attributed to Scaldicetus and the invalid species and incorrectly named specimens assigned to Scaldicetus (Table 2).
Table 2. Overview of all recorded Scaldicetus species and specimens
1 du Bus (Reference du Bus1872) originally named the holotype (IRSNB M.523) E. mortezelensis, after which Abel (Reference Abel1905) referred to the specimen as S. mortselensis. Lambert (Reference Lambert2008) restored the original name.
2 Also referred to as Scaldicetus bellunensis (Pilleri, Reference Pilleri1985; Pilleri, Reference Pilleri1986c).
3 Solely based on remains of a maxillary and mandible and some isolated teeth (Dal Piaz, Reference Dal Piaz1916: pl. I).
4 The holotype of S. grandis (IRSNB M.518) was referred to as Paleodelphis grandis (du Bus, Reference du Bus1872).
5 Originally named Physodon leccense (Gervais, Reference Gervais1872), but the location of the holotype is unknown (Pilleri, Reference Pilleri1986b, Reference Pilleri1986c).
6 Originally named Hoplocetus minor (Portis, Reference Portis1885).
7 Chapman (Reference Chapman1917) mentioned a Balcombian (Middle Miocene) or Oligocene age for S. lodgei.
8 The possibility cannot be excluded that the single tooth described as S. perpinguis is in fact the tusk of a ziphiid (Lambert et al., Reference Lambert, Bianucci and Post2010a: Fig. 3).
9 Originally referred to as Physeteroidea gen. et sp. indet. (Hasegawa et al., Reference Hasegawa, Takakuwa and Nakajima2001).
In line with the conclusions of Bianucci & Landini (Reference Bianucci and Landini2006) and Lambert & Bianucci (Reference Lambert and Bianucci2019), former Scaldicetus species outside of the type material of Scaldicetus caretti solely defined by large isolated teeth are referred to as Physeteroidea indet. The specimens described by Hasegawa et al. (Reference Hasegawa, Takakuwa and Nakajima2001), Estevens & Antunes (Reference Estevens and Antunes2004), Kimura et al. (Reference Kimura, Hasegawa and Barnes2006) and Toscano et al. (Reference Toscano, Abad, Ruiz, Muñiz, Álvarez, García and Caro2013) all have been assigned to Scaldicetus, because these authors consider Scaldicetus to be a wastebasket genus for large enamel-capped physeteroid teeth or other less complete physeteroid fossils such as dentaries. We would suggest to formally refer to these and future isolated dental specimens as Physeteroidea indet. Kimura et al. (Reference Kimura, Hasegawa and Barnes2006) wrote in their paper: ‘The size and general shape of the teeth GMNH-PV-581 and INM-4-012885 are also similar to the teeth of the holotype of B. shigensis, and there are no substantial morphological differences between all of these specimens’ (p. 8). In addition to this, both specimens and B. shigensis were found in Middle/Upper Miocene deposits. Therefore, we would cautiously suggest to classify GMNH-PV-581 and INM-4-012885 as Physeteroidea indet. aff. Brygmophyseter shigensis. This indicates that both specimens have affinity to B. shigensis, but are not from the same species and probably belonged to a close relative.
Conclusions
MAB13159 belonged to a macroraptorial sperm whale with a Late Miocene age. Based on the great resemblance to the type series of Scaldicetus caretti, we prefer to assign this physeteroid tooth to Physeteroidea indet. cf. Scaldicetus caretti.
Acknowledgements
We like to thank the reviewers Mark Bosselaers, Giovanni Bianucci and a third anonymous reviewer for their helpful comments that greatly improved the quality of the manuscript. Furthermore, we like to thank Maite Philippa for her help with making the pictures of the tooth and Bram Langeveld from the National History Museum Rotterdam for providing literature.
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