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Sharks from the Middle-Late Devonian Aztec Siltstone, Southern Victoria Land, Antarctica

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Sharks from the Middle-Late Devonian Aztec Siltstone, Southern Victoria Land, Antarctica Records of the Western Australian Museum 17: 287-308 (1995). Sharks from the Middle-Late Devonian Aztec Siltstone, southern Victoria Land, Antarctica John A. Longl and Gavin C. Young2 I Western Australian Museum, Francis Street, Perth, Western Australia 6000 2 Australian Geological Survey Organisation, p.a. Box 378, Canberra, A.C.T. 2601 Abstract Shark teeth representing three new taxa are described from the Middle-Late Devonian Aztec Siltstone of southern Victoria Land, Antarctica. Portalodus bradshawae gen. et sp. novo is represented by large diplodont teeth which have a base with a well-produced labial platform. It occurs in the middle to upper sections of the Aztec Siltstone. Aztecodus harmsenae gen. et sp. novo is represented by broad bicuspid teeth, wider than high, with numerous medial crenulations and twin nutritive foramina penetrating the rectangular base. It occurs in the middle sections of the Aztec Siltstone. The teeth of Anareodus statei gen. et sp. novo are characterised by having a main cusp which is more than twice as high as the second cusp, a small cusplet developed on the outer cutting edge of the main cusp, sometimes with few crenulations developed in the middle of the two cusps, and the base is strongly concave. Antarctilanma cf. prisca Young, 1982 is also recorded from the middle and upper sections of the Aztec Siltstone above the thelodont horizons and occurring with phyllolepids and Pambulaspis in the Cook Mountains section south of Mt Hughes. The chondrichthyan fauna from the Aztec Siltstone now contains at least 5 species, being the most diverse assemblage of Middle Devonian chondrichthyans (based on teeth) from one stratigraphic unit. INTRODUCTION the first illustrations of the large diplodont teeth Fossil shark remains were first identified in the from Portal Mountain recorded by Ritchie (1971) Devonian Aztec fish fauna of southern Victoria as resembling those of Xenacanthus sp. These shark Land in the material collected from moraine at remains form part of a diverse fish fauna from the Granite Harbour, near the coast of McMurdo Aztec Siltstone, including arthrodires (Ritchie 1975; Sound, during the British Antarctic 'Terra Nova' Long in press), antiarchs (Young 1988), Expedition of 1910-13. Among the fish scales acanthodians (Young 1989b), rhipidistians (Young observed in thin section were some which et al. 1992), lungfish (Woolfe et al. 1990, Young Woodward (1921: 57) described as 'typically 1991), and an undescribed actinopterygian (Young Elasmobranch, each large cusp showing a trace of 1991). The faunal list now stands at 22 named an original pulp cavity'. Many of these scales genera and 31 species, including the new forms subsequently turned out to be thelodont scales, described here, of which all species and 18 genera whose existence in a fish fauna of Late Devonian are endemic to the region of East Gondwana (Table aspect was completely unsuspected by Woodward 1). and other early workers. These were recently The material described herein comes mainly described as a new species of Turinia by Turner from a new collection of Aztec Siltstone fossils and Young (1992). White (1968), who studied the made by J. Long on the joint 1991/92 New Zealand first in situ material, collected by B.M. Gunn and Antarctic Research Program-Australian National G. Warren during the Trans-Antarctic Expedition Antarctic Research Expedition trip to the Cook of 1958 (Gunn and Warren 1962), then found one Mountains and SkeIton Neve regions, but also definitive shark specimen, a single tooth which he includes shark material previously collected by A. described as a new form, Mcmurdodus featherensis, Ritchie and G.c. Young during the Victoria placed in a new family Mcmurdodontidae. This University of Wellington Antarctic Expedition specimen came from Mt Feather, 18 km due east of VUWAE 15 (1970/71 season). The new material is the Lashly Range (Figure 1). Young (1982) sufficient to describe three new genera of Devonian described a second shark, Antarctilanma prisca, sharks, based on teeth. In addition, information based on partially articulated remains which from the new localities in the Cook Mountains included teeth, scales and fin-spines also provided extends the known stratigraphic range of 288 J.A. Long, G.c. Young Table 1 Vertebrate faunal list for the Aztec Siltstone, Antarctilamna prisca. Specimens are lodged in the Antarctica. Western Australian Museum, Perth (prefix WAM), the Australian Museum, Sydney (prefix AMF), and AGNATHA Turinia antarctica Turner and Young, the Commonwealth Palaeontological Collection, 1992 Australian Geological Survey Organisation, PLACODERMI Canberra (prefix CPC). Antiarchi Bothriolepis antarctica Woodward, 1921 B. alexi Young, 1988 LOCALITY INFORMAnON B. askinae Young, 1988 Full details of all fossil fish localities known to B. barretti Young, 1988 that time from the Aztec Siltstone were provided B. karawaka Young, 1988 by Young (1988). Information is given below for B. kohni Young, 1988 new localities and previous localities yielding B. macphersoni Young, 1988 described shark material. Numbers refer to B.mawsoniYoung,1988 localities 1-24 of Young (1988, figure 3). The B. portalensis Young, 1988 B. vuwae Young, 1988 regions are dealt with here from south to north. B. sp. indet 1-13. Pambulaspis antarctica Young, 1989 Cook Mountains Arthrodira Antarctolepis gunni White, 1968 Several new sites were discovered in the Cook Groenlandaspis antarcticus Ritchie, Mountains during the 1991/92 field season (Figure 1975 1, left). Shark teeth were recovered from "Gorgon's Groenlandaspis spp. Head" near Mt Hughes, the same area from where Boomeraspis goujeti Long, 1995a fish were first recorded during the 1988/89 season phlyctaeniids spp. (Woolfe et al. 1990). Other material came from the Phyllolepida ?Austrophyl/olepis sp. Fault Bluff sections and at Mt Gudmundson. phyllolepid indet. Stratigraphic sections of the Aztec Siltstone and Beacon Heights Orthoquartzite from these lncertae sedis Antarctaspis mcmurdoensis White, 1968 localities were measured by M. Bradshaw and F. CHONDRICHTHYES Harmsen and are currently being compiled. Figure Mcmurdodus featherensis White, 1968 2 shows the provisional stratigraphic position of Antarctilamna prisca Young, 1982 the fish faunas from the Cook Mountains referred Anareodus statei gen. et sp. novo to in the text, based on field measurement of Aztecodus harmsenae gen. et sp. novo stratigraphic sections. Portalodus bradshawae gen. et sp. novo Fault Bluff, "fish hotel" section ACANTHODlI Gyracanthides warreni White, 1968 This stratigraphic section was measured along a Antarctonchus glacialis White, 1968 low ridge running north-south outcropping Byssacanthoides debenhami Woodward, 1921 immediately north of Fault Bluff (79°18'5, 157° Culmacanthus antarctica Young, 1989 41 'E). The stratigraphic sections were logged by M. Cheiracanthoides sp. (scales). Bradshaw and F. Harmsen. A continuous outcrop lschnacanthid gen. indet. of Aztec Siltstone approximately 91 m thick is exposed here, although the base of the section is OSTEICHTHYES covered by scree. By comparison with the Actinopterygii palaeoniscoid gen. novo surrounding outcrops, the top of the Beacon ?palaeoniscoid indet. Heights Orthoquartzite would sit within 20 m of Rhipidistia Gyroptychius? antarcticus the base of the section. Several fossil fish bearing (Woodward) horizons were located: site "A", about 45 m above Koharalepis jarviki Young et al., 1992 the base, contained isolated impressions of fish Mahalalepis resima Young et al., 1992 plates in hard white orthoquartzite; site "B", about Platyethmoidea antarctica Young et al., 67 m above the base, has rich accumulations of 1992 well-preserved fish remains in a medium-coarse to Vorobjevaia dolonodon Young et al., gritty quartzose sandstone; site "M", about 72 m 1992 above the base, is a fine, green siltstone with small Notorhizodon mackelveyi Young et al., fragments of well-sorted fish bone and scale debris; 1992 site "Y" about 85 m above the base, has occasional porolepiform indet. fish plates in quartz sandstone; and site "2", at the Dipnoi ? Eoctenodus sp. top of the exposure about 88-90 m above the base, Howidipterus sp. is a clean, indurated orthoquartzite rich in fish and ?ctendontid indet. plant remains. Lycopod stem axes are here Devonian sharks from Antarctica 289 N ~ /i ~I \) a: sect:~ ~;~en.............. ~ I ~-- -~'--~ ~ I section LA . / -'\ () a: lJJ- \ ~zl I . \ A .. .. '-- ~. '~\~ ! -(-------- )....11.·····-.. " ;1--I ~/j Mt. Gudmundson ! : ~I V ~\ % 79015' \ ,~I \ -.j \ \ ~ . 1'7 ~) ·-.VA~ ~ / Fish Hotel site \1 _/ Portal Mountain Fault Bluff ~ ~', (1'-\ (1\)(0\ iW - ,"'- ~ ~ 31/12/91 I \"dJ •.0. ;,<' \ , \ ~ \ Ml(Q IUJ lNJr/P\ lllNJ \,.. \ \ I l. Campsite \, I :0: C-130 landing site I I I o Depot I / I I I I I ,I I \ MUlgrew \ \ \ Nunatak \ t<- \ , , \ \ , \~ \ \ \ -- \ '-::' flI- \ \ -..9 \ \ , -.,> \I \ \ 'f " \ \ ""- , \ \ I ! Figure 1 Locality map showing sites visited during the 1991/92 field expedition and localities mentioned in the text. 290 I.A. Long, G.c. Young preserved as 3-D impressions (McLoughlin and conglomerate, and site "6", about 90 m above the Long 1994). base in the highest exposure of flat-lying sandstones of the Aztec Siltstone, also a gritty layer Mt Gudmundson with abundant fish bones. Some scree material Approximately 93 m of Aztec Siltstone is containing fish fossils in a coarse sandstone was exposed here in continuous outcrop, conformably found in between sites 5 and 6 and labelled as site resting upon a thick exposure
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