Introduction
Fossil insects have been reported from different outcrops in Antarctica: Permian Polarstar Formation, Sentinel Mountains (Hemiptera: Stenoviciidae; Tasch & Riek Reference Tasch and Riek1969), Permian Theron Mountains (Hemiptera; Plumstead Reference Plumstead1962, Carpenter Reference Carpenter1969), Permian Mount Glossopteris Formation, Ohio Range (Plecoptera; Carpenter Reference Carpenter1969, Sinitshenkova Reference Sinitshenkova1987), Jurassic Mount Flora, Hope Bay, Grahamland (Coleoptera; Zeuner Reference Zeuner1959, Carpenter Reference Carpenter1969, Tasch Reference Tasch1970, Reference Tasch1973), Jurassic Victoria Land (Odonata, Blattodea, Coleoptera; Carpenter Reference Carpenter1969, Bomfleur et al. Reference Bomfleur, Schneider, Schöner, Viereck-Götte and Kerp2011, Santos Filho et al. Reference Santos Filho, Brum, Souza, Figueiredo, Usma and Ricetti2023) and Pliocene to mid-Miocene Meyer Desert Formation, Transantarctic Mountains (Coleoptera; Ashworth & Kuschel Reference Ashworth and Kuschel2003). Similarly, Bomfleur et al. (Reference Bomfleur, Schneider, Schöner, Viereck-Götte and Kerp2011) mentioned an isolated beetle elytra of the Triassic Section Peak Formation, southern north Victoria Land, but without providing further taxonomic identification.
The Transantarctic Mountains preserve a Late Palaeozoic to mid-Mesozoic sedimentary succession (Beacon Supergroup) that has been intensively studied since the beginning of major geological field campaigns in the area in the late 1950s (e.g. McKelvey & Webb Reference McKelvey and Webb1961, Faure & Mensing Reference Faure and Mensing2010). The Triassic fluvio-lacustrine deposits of the Victoria Group (Permian-Triassic) in particular have become known for their rich and diverse assemblages of vertebrate remains (Barrett et al. Reference Barrett, Baillie and Colbert1968, Hammer Reference Hammer, Taylor and Taylor1990, Sidor et al. Reference Sidor, McIntosh, Gee, Hammer, Makovicky and Smith2023) and well-preserved plant fossils (Schopf Reference Schopf1970, Taylor & Taylor Reference Taylor1990, Escapa et al. Reference Escapa, Taylor, Cuneo, Bomfleur, Bergene and Serbet2011).
In light of the numerous collections and large numbers of fossil specimens that have been accumulated since then, it is surprising that not a single invertebrate body fossil has been described from the Triassic of Antarctica so far. As a first step towards filling this gap, we here present an isolated insect forewing from Triassic deposits of the Eisenhower Range, northern Victoria Land, Antarctica. Therefore, in this paper, we report and describe the first insect record for the Triassic of Antarctica, representing the finding of a mecopteran that is novel for this continent.
Materials and methods
The specimen GXIII-SETI02-025 was collected during the course of the 13th German Antarctic North Victoria Land Expedition (GANOVEX XIII, 2018/2019) from a previously unvisited outcrop of the Section Peak Formation exposed along a prominent escarpment about halfway between Eskimo Point and Timber Peak, northern Eisenhower Range, East Antarctica (74°14’50"S, 162°28’47"E; Fig. 1. This lower part of the Section Peak Formation is made up of epiclastic sandstone and mudstone with intercalated coal seams (Schöner et al. Reference Schöner, Bomfleur, Schneider and Viereck-götte2011), and it is dated as Late Triassic based on palynostratigraphic data (Bomfleur et al. Reference Bomfleur, Schöner, John, Schneider, Elsner, Viereck- Götte and Kerp2014). At the study site, one particular siltstone bed in the central part of the section has yielded a mass occurrence of narrow-leaved Dicroidium fronds and Linguifolium leaves. An otherwise-barren bedding surface on the flipside of one plant fossil-rich specimen contains the insect wing fragment.
Field images of the new fossil locality. a. View west onto the escarpment of the Polar Plateau along the Eisenhower Range between Eskimo Point in the south and Mount New Zealand in the north, with an arrow indicating the fossil site on the Antarctic continent and an star marking the position of the outcrop where the specimen was collected. b. Mass accumulations of plant debris on a freshly exposed bedding surface at the new fossil site. Photographs by Jan Unverfärth.
The specimen was examined and photographed using a Canon EOS 5D Mark IV camera with a Canon MP-E 65 mm f/2.8 1–5× Macro Photo lens under polarized light with a circular analyser at sub-maximum extinction. Line drawings were prepared from the photographs using CorelDraw 7 image editing software.
The venational nomenclature is based on Willmann (Reference Willmann1989), Minet et al. (Reference Minet, Huang, Wu and Nel2010) and Bashkuev & Sukatsheva (Reference Bashkuev and Sukatsheva2021). The specimen GXIII-SETI02-025 is housed at the palaeobotanical collections of the University of Münster, Münster, Germany. Forewing venation abbreviations: Sc = subcosta; ScP = posterior subcosta; R = radius; Rs = radius sector; pt = pterostigma; M = median vein; CuA = anterior cubitus.
Systematic palaeontology
Order MECOPTERA Packard, Reference Packard1886
Family PERMOCHORISTIDAE Tillyard, Reference Tillyard1917
Subfamily PERMOCHORISTINAE Tillyard, Reference Tillyard1917
(Fig. 2)
Specimen GXIII-SETI02-025 (Mecoptera: Permochoristidae) from the lower part of the Section Peak Formation (Upper Triassic), northern Eisenhower Range, northern Victoria Land, East Antarctica. a. Photograph of the forewing. b. Line drawing of the forewing. Scale bar = 1 mm. See text for abbreviations.
Referred material
GXIII-SETI02-025 imprint of fragmentary forewing, with basal part missing.
Locality
Lower part of the Section Peak Formation (Upper Triassic), northern Eisenhower Range, northern Victoria Land, East Antarctica (74°14’50"S, 162°28’47"E; Fig. 1).
Description
The forewing is very small (with a preserved length of only 8.2 mm), sub-oval in shape and completely flattened; the membrane appears rather soft and without distinct corrugation or sculpture (Fig. 2). The basal and apical regions are not preserved, and the basal connections of the main veins are not preserved. The anterior margin is slightly convex, with a long concave course at the distal end of R1. The venation is strongly reduced, with only few, vaguely visible cross-veins. The Sc is short, very slightly sigmoidal and ending in the anterior margin far proximally from the mid-wing. The pterostigma (pt) is partially visible, in coloured pigment, and is nearly lanceolate and elongate. R1 is long and straight, ending in the proximal third of the concave course of the anterior margin. Rs and M bifurcate at the same level. Rs is basally bifurcate at the level of the distal end of ScP, with five terminal branches (Rs1 (bifurcated), Rs2, Rs3 and Rs4) running parallel to each other and reaching the apical margin, with an additional short fork on Rs1. Rs1+2 is forked apical of the Rs3+4 fork. Stem M is long, straight and divided into two main branches (MP1+2 and MP3+4) at the same level as the forking of Rs. M is five-branched (with additional forks on M4). M1+2 is forked distal of the bifurcation of Rs1+2. CuA remains visible. There is a distinctive stained colour pattern in the forewing.
Discussion
The general wing shape and venation are consistent with the ground pattern of Permian and Triassic Mecoptera. Based on the reduced venation, we tentatively identify specimen GXIII-SETI02-025 as belonging to the Mecoptera Packard, Reference Packard1886, with a probable affiliation within Permochoristidae Tillyard, 1917 based on the well-developed pterostigma, the dichotomously branched Rs and with Rs and M having five branches each (10 branches in total). The preserved venation appears to be of the typical scheme of Permochoristinae Tillyard 1917 sensu Novokshonov (Reference Novokshonov1997b; e.g. Rs is not pectinate with four to five branches - an additional fork on Rs1 may be an individual variation; M with five veins with forks on M4), but due to the rather incompletely preserved wing base, and thus without clear knowledge of the basal connection of the main veins, we prefer a determination under open nomenclature until more material of this taxon is available.
Specimen GXIII-SETI02-025 differs from Triassic genera of Permochoristidae Tillyard, 1917 (e.g. Duraznochorista Lara & Bashkuev, Reference Lara and Bashkuev2020, Upper Triassic of Argentina; Mesochorista Tillyard, Reference Tillyard1916, Middle Triassic of China, Middle-Upper Triassic of Kyrgyzstan, Upper Triassic of Australia and Kazakhstan; Agetopanorpa Carpenter, Reference Carpenter1930, Middle Triassic of China, Middle-Upper Triassic of Kyrgyzstan; Hongchoristites Rivaz Hernández, Reference Rivaz Hernández2018, Middle-Upper Triassic of China; Kalochorista Lin, Reference Lin1992, Upper Triassic of China; Mesageta Novokshonov, Reference Novokshonov1997a, Middle-Upper Triassic of Kyrgyzstan; Xenochoristella Riek, Reference Riek1955, Upper Triassic of Australia; Qingochorista Guo & Hong, Reference Guo and Hong2003, Middle Triassic of China) in: Sc is probably simple, Rs1+2 and Rs3+4 stem and M1+2 and M3+4 stem long, Rs1 is twice branched and M2 is unbranched.
Superficially similar members of the extinct family Permochoristidae Tillyard, 1917 are distributed widely from the Permian to the Jurassic in South Africa, Australia, Asia, Europe, South America and North America (e.g. Carpenter Reference Carpenter1930, Riek Reference Riek1953, Reference Riek1955, Reference Riek1976, Pinto Reference Pinto1972, Papier et al. Reference Papier, Nel and Grauvogel-Stamm1996, Novokshonov 1997a,b,c, 2001, Van Dijk & Geertsema Reference Van Dijk and Geertsema1999, Guo & Hong Reference Guo and Hong2003, Bashkuev Reference Bashkuev2010, Lin et al. Reference Lin, Nel and Huang2010, Lara et al. Reference Lara, Bashkuev and Wang2015, Lara & Bashkuev Reference Lara and Bashkuev2020, Lian et al. Reference Lian, Cai and Huang2022, Reference Lian, Cai and Huang2023; PaleoBioDB). However, they were dominant among mecopteran faunas throughout the Permian, but they decreased greatly in diversity and abundance from the Triassic (probably impacted by the end-Permian mass extinction event) until becoming quite rare in the Jurassic, being replaced by more derived groups (Lara et al. Reference Lara, Bashkuev and Wang2015, Lian et al. Reference Lian, Cai and Huang2023). Triassic permochoristids are known mainly from Central Asia and Australia (Riek Reference Riek1955, Novokshonov Reference Novokshonov1997c, Reference Novokshonov2001) and from rare specimens recorded from Europe, South Africa, South America (Argentina) and China (Riek 1974, Papier et al. Reference Papier, Nel and Grauvogel-Stamm1996, Guo & Hong Reference Guo and Hong2003, Lara et al. Reference Lara, Bashkuev and Wang2015, Lara & Bashkuev Reference Lara and Bashkuev2020). Therefore, the new fossil described herein, besides representing the first record of Mecoptera from the continent, supports the worldwide distribution and a greater diversity of the Permochoristidae during Triassic times.
Conclusions
The paucity of insect fossils and – as a consequence - of reported insect-mediated herbivore damage in plant-fossil assemblages from the Antarctic Triassic compared to coeval assemblages from, for example, South Africa (Scott et al. Reference Scott, Anderson and Anderson2004) has previously been speculated to reflect a latitudinal gradient, with decreased insect diversity at the very high palaeolatitudinal setting of the Antarctic sites (Bomfleur et al. Reference Bomfleur, Schneider, Schöner, Viereck-Götte and Kerp2011).
In this respect, our report of the first insect forewing fossil from the Antarctic Triassic may support an alternative interpretation: that such small and inconspicuous fossils might have been overlooked previously. We anticipate that future dedicated searches through the extensive available collections could reveal the Antarctic Triassic invertebrate fossil record to be richer than previously thought.
Acknowledgements
We are grateful to Elke Gröning (Clausthal-Zellerfeld) for a first discussion of the fossil. CB wants to express his sincerest thanks to the late Rafael Gioia Martins-Neto and to the late Irajá Damiani Pinto for their scientific exchange and friendship. We acknowledge Dr Cliff Atkins (Editor) and two anonymous reviewers for their valuable comments and suggestions regarding the first version of this manuscript. We thank Andreas Läufer and the Bundesanstalt für Geowissenschaften und Rohstoffe (Hannover) for the invitation to join the GANOVEX XIII expedition, the Alfred-Wegener Institute (Bremerhaven), the Swedish Polar Research Secretariat (Luleå) and Helicopters Support International (Wanaka) for technical support.
Financial support
This work was supported by contributions from the Ymer-80 and Carl Tryggers foundations (CTS 20: 300 to TM) and the Deutsche Forschungsgemeinschaft (DFG project BO3131/1-1 to BB).
Competing interests
The authors declare none.
Author contributions
JU and TM performed the fieldwork. MM surveyed the fossil assemblage and photographed the material. MBL, BB and CB analysed the material. All authors discussed the results, wrote the manuscript and provided illustrations.
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