Monday 16 November 2015

Turtle remains from the Late Miocene to Early Pliocene Black Rock Sandstone of Victoria, Australia.

Australia has a diverse assemblage of Sea Turtles today, with six of the seven living Sea Turtle species found in Australian waters and one found nowhere else. The continent also has an extensive fossil record of Cretaceous Turtles, but no post-Cretaceous fossil Turtles have been found in Australia to date. This is odd, as Turtles have excellent preservational potential, having dense bony shells and spending much of their lives in shallow marine environments, and because Cainozoic fossil Turtles are known from New Guinea and New Zealand, making it highly unlikely that Sea Turtles were absent from Australia during this time.

In a paper published in the journal Alcheringa on 16 October 2014, Erich Fitzgerald and Lesley Kool of Geosciences at Museum Victoria describe the discovery of fragmentary Turtle remains from the Late Miocene to Early Pliocene Black Rock Sandstone at Beaumaris on Port Philip Bay in Victoria State, Australia.

The Black Rock formation is noted for a diverse vertebrate assemblage, including Sharks and Rays, Bony Fish, Penguins, other Seabirds, Sireneans, Seals, Baleen and Toothed Whales, and some terrestrial Birds and Marsupials, as well as invertebrates such as Molluscs and Echinoderms and microfossils such as Foraminiferans.

Only two Turtle bones were recovered from the site, an almost complete dentary (lower jawbone) and the proximal tip of a costal bone (plate on the dorsal portion of the shell derived from a modified rib). This is not enough to assign the remains to any particular Turtle, though they do resemble other specimens assigned to the genus Pacifichelys, which has previously been described from California and Peru.

Isolated proximal end of a costal of an unidentified Turtle in: (A, dorsal; (B) visceral; and (C) proximal views. Specimen whitened with ammonium chloride. Fitzgerald & Kool (2014).

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