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Crossopterygian Fishes from the Devonian of Antarctica: Systematics, Relationships and Biogeographic Significance

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Crossopterygian Fishes from the Devonian of Antarctica: Systematics, Relationships and Biogeographic Significance AUSTRALIAN MUSEUM SCIENTIFIC PUBLICATIONS Young, Gavin C., John A. Long and A. Ritchie, 1992. Crossopterygian fishes from the Devonian of Antarctica: systematics, relationships and biogeographic significance. Records of the Australian Museum, Supplement 14: 1–77. [7 May 1992]. doi:10.3853/j.0812-7387.14.1992.90 ISSN 0812-7387, ISBN 0-7305-9717-2 Published by the Australian Museum, Sydney naturenature cultureculture discover discover AustralianAustralian Museum Museum science science is is freely freely accessible accessible online online at at www.australianmuseum.net.au/publications/www.australianmuseum.net.au/publications/ 66 CollegeCollege Street,Street, SydneySydney NSWNSW 2010,2010, AustraliaAustralia Records of the Australian Museum (1992) Supplement 14. ISBN 0 7305 9717 2 Crossopterygian Fishes from the Devonian of Antarctica: Systematics, Relationships and Biogeographic Significance GAVIN C. YOUNG!, JOHN A. LONG2 & ALEXANDER RITCHIE3 IBureau of Mineral Resources, PO Box 378, Canberra, ACT 2601, Australia 2Westem Australian Museum, Francis Street, Perth, W A 6000, Australia 'Australian Museum, PO Box A285, Sydney South, NSW 2000, Australia ABSTRACT. Four new genera of osteolepifonns and a new rhizodontifonn genus are described from the Middle-Late Devonian Aztec Siltstone (Beacon Supergroup) of Antarctica. Other indetenninate osteolepid, eusthenopterid and rhizodontid remains, and a single indetenninate porolepifonn scale, are described from the same fonnation. Koharalepis jarviki n.gen., n.sp. is a large cosmine-covered osteolepifonn with a broad flat head, two pairs of dennosphenotics, large extratemporals, a large postorbital in the cheek which does not reach the orbit, an elongate jugal, lachrymal separating the maxilla from the premaxilla at the jaw margin, and large anteriorly pointed median and triangular lateral extrascapulars. It is placed with Canowindra Thomson and Beelarongia Long in the new family Canowindridae. Platyethmoidia antarctica n.gen., n.sp. is a poorly known form with a very broad, flat fronto-ethmoidal shield with dorsomesially oriented slit-like nares, and a lower jaw with a deep articular region. It may be closely related to Gyroptychius? australis Young & Gorter. Mahalalepis resima n.gen., n.sp. is interpreted on the morphology of the fronto­ ethmoidal shield as an early megalichthyid, and a new definition of this family is presented. Vorobjevaia dolonodon n.gen., n.sp. is a poorly known osteolepid with a distinctive jaw morphology. The rhizodontifonn Notorhizodon mackelveyi n.gen., n.sp. was the largest fish in the Aztec fauna, attaining a length of over 3 m. It is characterised by elongate frontals and small dennosphenotics in the skull, Rhizodus-type tusks, and strong tooth flanges on the coronoid and dennopalatine series bones in the jaws. The braincase in a rhizodontifonn is described for the first time, and in general morphology closely resembles that of Osteolepifonnes. Notorhizodon resembles Screbinodus Andrews in dennal ornament and Barameda Long in skull pattern. All previously described crossopterygian material from the Aztec Siltstone is revised, and Gyroptychius antarctic us (Smith Woodward) is regarded as a nomen nudum. The stratigraphic distribution of rhipidistians in the Aztec Siltstone is summarised, and the biogeography and phylogenetic relationships of the 2 Records of the Australian Museum (1992) Supplement 14 new taxa discussed. The canowindrids were an endemic group of East Gondwana. The megalichthyids and rhizodontiforms may have originated in the East Gondwana Province during the Middle Devonian, but did not reach Euramerica until the uppermost Late Devonian. They flourished in the Carboniferous Period following the decline of the eusthenopterids and the initial radiation of tetrapods. YOUNG, G.c., l.A. LONG & A. RITCHIE, 1991. Crossopterygian fishes from the Devonian of Antarctica: systematics, relationships and biogeographic significance. Records of the Australian Museum Supplement 14: 1-77. Contents Introduction ............................................................................................................................................... 2 Materials and Methods ............................................................................................................................ 5 Geographic and Stratigraphic Distribution ........................................................................................... 6 Biostratigraphy and Age ......................................................................................................................... 8 Systematic Palaeontology ........................................................................................................................ 9 Class Osteichthyes ................................................................................................................................... 9 Subclass Sarcopterygii ............................................................................................................................. 9 Order Osteolepiformes Jarvik, 1942 ...................................................................................................... 9 Canowindridae n.fam ............................................................................................................................... 9 Koharalepis n.gen .................................................................................................................................... 9 Koharalepis jarviki n.sp ......................................................................................... ;.............................. 10 Family Megalichthyidae ........................................................................................................................ 20 Mahalalepis n.gen .................................................................................................................................. 21 Mahalalepis resima n.sp ....................................................................................................................... 22 Family incertae sedis ............................................................................................................................ 23 Platyethmoidia n.gen ............................................................................................................................. 23 Platyethmoidia antarctica n.sp ............................................................................................................. 23 Vorobjevaia n.gen .................................................................................................................................. 26 Vorobjevaia dolonodon n.sp ................................................................................................................. 26 osteolepid gen. et sp. indet. ................................................................................................................ 28 eusthenopterid gen. et sp. indet. ......................................................................................................... 32 Order Rhizodontiforrnes ........................................................................................................................ 33 Notorhizodon n.gen ................................................................................................................................ 33 Notorhizodon mackelveyi n.sp .............................................................................................................. 33 rhizodontiform gen. et sp. indet. ........................................................................................................ 58 Order Porolepiforrnes ............................................................................................................................. 59 porolepiform gen. et sp. indet. ............................................................................................................ 59 Discussion ............................................................................................................................................... 59 Phylogenetic Relationships .................................................................................................................... 59 Biogeographic Relationships ................................................................................................................. 69 Acknowledgments ................................................................................................................................... 70 References ............................................................................................................................................... 70 Appendix I (Tables I ,2) ....................................................................................................................... 74 Appendix 11 (Abbreviations used in Figures) .................................................................................... 76 Crossopterygian fishes from Antarctica were first Woodward (1908) in a Tertiary vertebrate assemblage recognised by Woodward (1921) in his original description from Seymour Island, just off the Antarctic Peninsula, of the Devonian fish material discovered during the but the Mount Suess discovery was the first of Devonian British Antarctic 'Terra Nova' expedition of 1910-1913. fossils, and of fossil vertebrates, on the Antarctic The original collection was made by T. Griffith Taylor's continent itself. The provenance of the fossiliferous
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