Paper No. 2
Presentation Time: 1:45 PM
Early Cretaceous Trace and Body Fossils In Australia Establish the Oldest Known Gondwanan Crayfish In Their Probable Place of Origin
In 1879, Thomas H. Huxley predicted that fossil evidence in freshwater deposits of Australia and elsewhere in the Southern Hemisphere would help to corroborate the evolutionary heritage of parastacid crayfish. Nearly 130 years later, we are pleased to report the discovery of both trace and body fossil evidence of parastacids in Early Cretaceous (Albian-Aptian) freshwater deposits of Victoria, Australia. We thus verify Huxley's supposition, while also announcing the oldest known freshwater parastacid crayfish from Gondwana. Parastacid body fossils include a partial abdomen (Palaeoechinastacus australianus, gen. et sp. nov.) and two chelae, coming from fluvial deposits in the Otway Group (Albian). Trace fossils in fluvial deposits of the Otway Group and Strzelecki Group (Aptian), which are mostly variants of Thalassinoides, closely resemble modern parastacid burrow systems. These trace fossils thus independently support a crayfish presence while also revealing their burrowing habits during the Early Cretaceous in Australia. Interestingly, this region was at high latitudes (nearly 80° S) and periglacial in places, indicating that these crayfish, like some modern parastacids in Tasmania, were adapted to cold-water ecosystems. Consequently, this combined fossil evidence provides new insights on the paleoecology and evolutionary history of Mesozoic parastacids in Australia. These body and trace fossils also support molecular phylogenies suggesting that parastacid crayfish radiated from southeastern Australia prior to the final fragmentation of Gondwana. Our exciting discoveries, in combination with a recent interpretation of parastacid trace fossils in the Late Jurassic-Late Cretaceous of Argentina, more clearly document the long-unrecognized geologic history of parastacids in Gondwana, predicted long ago by Huxley.