Relative age of the Devonian tetrapod Metaxygnathus, based on the associated fossil fish assemblage at Jemalong, New South Wales

Abstract

A new genus, Jemalongia, is erected for a porolepiform shoulder girdle and associated scales from the Cloghnan Shale at Jemalong Weir, near Forbes in New South Wales, Australia. There is no evidence for the Late Devonian porolepiform Holoptychius that was previously associated with the tetrapod Metaxygnathus at this site. Scales and a partial articulated specimen of Holoptychius sp. from the Famennian Worange Point Formation at Eden on the New South Wales south coast are close to both Holoptychius sp. from East Greenland and Holoptychius nobilissimus from Scotland. However, evidently a species other than Holoptychius sp. is represented by scales in the Hunter Siltstone at Grenfell, central New South Wales. The Jemalong fossils share character states with other scales from Grenfell and Bogan Gate that show features resembling coelacanth scales; a scale attributed to the Devonian coelacanth Gavinia is shown here for comparison. An isolated tooth plate demonstrates a second lungfish taxon at Jemalong, in addition to the denticulate Soederberghia sp. There is insufficient evidence for referring the skull of Soederberghia to the type species Soederberghia groenlandica. Incomplete placoderm remains suggest that a new antiarch taxon may occur at Jemalong. This new evidence suggests that the age of the Jemalong assemblage should be revised downwards to Givetian–Frasnian or older, rather than Famennian as previously interpreted. Gavin C. Young [Gavin.Young@anu.edu.au; Gavinyoung51@gmail.com], Department of Materials Physics, Research School of Physics, Australian National University, Canberra, Australia; Australian Museum Research Institute, 1 Williams St, Sydney 2010, New South Wales, Australia.