New information on the giant Devonian lobe-finned fish Edenopteron from the New South Wales south coast

Abstract

Edenopteron, with a lower jaw some 48 cm long, and total length perhaps exceeding 3 m, is the largest Devonian lobe-fin known from semi-articulated remains. New material described from the type locality (Boyds Tower, south of Eden) includes three slightly smaller articulated skulls and jaws, and additional bones of the shoulder girdle. Another articulated skull roof, shoulder girdle and palate is described from a second locality (Hegarty Bay), about 10 km south of Boyds Tower. Both localities represent the upper part of the Worange Point Formation, of late Famennian age (uppermost Upper Devonian). The new morphological evidence supports a close relationship to the tristichopterids Mandageria and Cabonnichthys, from the slightly older (Frasnian, Upper Devonian) fossil fish assemblage at Canowindra, New South Wales. Features of the shoulder girdle (supracleithrum, anocleithrum) suggest that Edenopteron is more closely related to Mandageria than Cabonnichthys. Eight characters are used to define a tristichopterid subfamily Mandageriinae, to which Notorhizodon from the Middle Devonian of Antarctica is also referred. The Mandageriinae is endemic to East Gondwana (Australia–Antarctica). In combination with possibly the most primitive tristichopterid, Marsdenichthys from the Frasnian of Victoria, these distributions implicate East Gondwana as a likely place of origin for the entire group. This relates to the major but unresolved question of a possible Gondwana origin for all the land vertebrates (tetrapods).

• An endemic Gondwanan sub-group (Mandageriinae) of the Devonian fishes closest to land animals (tetrapodomorph tristichopterids) is confirmed.

• Retention of primitive features (e.g. accessory vomers) points to an earlier origin of the Mandageriinae in East Gondwana, consistent with the Victorian occurrence of another primitive tristichopterid (Marsdenichthys).

• Edenopteron is confirmed from a second south coast fossil site, and new characters indicate its closest relative is Mandageria from Canowindra, NSW.

• Congruent evidence of older Gondwanan occurrences in other groups (basal tetrapodomorphs, rhizodontids, canowindrids), and previously dismissed trace fossil evidence (Grampians trackways), implicate South China and East Gondwana as the likely place of origin for all land vertebrates.

Keywords:

• Devonian
• lobe-finned fish
• Edenopteron keithcrooki
• morphology
• stratigraphy
• biogeography

Acknowledgements

We thank Ben Young for assistance with fossil preparation, photography and fieldwork; Bruce Loombs and Monica Yeung for assistance with fieldwork at the Hegarty Bay fossil site (first discovered by Dr Anne Warren, Latrobe University). Dr A. Ritchie gave advice on the original Hegarty Bay excavation. For facilities in the Research School of Physics and Department of Applied Mathematics, ANU, we are indebted to Professors Tim Senden and Adrian Sheppard. For access to specimens in the Australian Museum and other help we thank Yong-Yi Zhen, Robert Jones and Matt McCurry. Fieldwork in the Ben Boyd National Park was covered by collecting permits from the NSW National Parks and Wildlife Service, and we thank Stephen Dovey and Craig Dickman for access to the Hegarty Bay site (2006–2008). A. Wall, S. Ferguson and G. Malolakis (NSW Office of Environment and Heritage, NPWS, South Coast Branch, Merimbula, NSW) facilitated visits to Ben Boyd National Park in 2019, and we thank S. Ferguson and G. Malolakis for assistance in the field. Finally, we thank J. Long and T. Holland for helpful reviews of the manuscript that greatly improved this paper.

Additional information

Funding

Excavation and preparation of the type material of Edenopteron keithcrooki supported by Australian Research Council Discovery Grants (DP0558499 and DP0772138). Jing Lu is supported by the Strategic Priority Research Program of the Chinese Academy of Sciences Grant No. XDB26000000 the National Natural Science Foundation of China Grant No. 41872023 and an ANU Department of Applied Mathematics Marcelja Fellowship.