The crocodylian fossil record from the Cenozoic of Australasia is notable for its rich taxonomic diversity, and is primarily represented by members of the clade Mekosuchinae. Reports of crocodylian fossils from Australia date back to the late nineteenth century. In 1886, Charles Walter de Vis proposed the name Pallimnarchus pollens for crocodylian fossils from southeast Queensland—the first binomen given to an extinct crocodylian taxon from Australia. Pallimnarchus has come to be regarded as a large, broad-snouted crocodylian from Australia’s Plio-Pleistocene, and numerous specimens, few of which are sufficiently complete, have been assigned to it by several authors throughout the twentieth century. In the late 1990s, the genus was expanded to include a second species, Pallimnarchus gracilis. Unfortunately, the original syntype series described as Pallimnarchus pollens is very fragmentary and derives from more than one taxon, while a large part of the subsequently selected lectotype specimen is missing. Because descriptions and illustrations of the complete lectotype do not reveal any autapomorphic features, we propose that Pallimnarchus pollens should be regarded as a nomen dubium. Following this decision, the fossil material previously referred to Pallimnarchus is of uncertain taxonomic placement. A partial skull, formerly assigned to Pallimnarchus pollens and known as ‘Geoff Vincent’s specimen’, possesses many features of diagnostic value and is therefore used as basis to erect a new genus and species—Paludirex vincenti gen. et sp. nov. A comprehensive description is given for the osteology of ‘Geoff Vincent’s specimen’ as well as aspects of its palaeoneurology, the latter being a first for an extinct Australian crocodyliform. The newly named genus is characterized by a unique combination of premaxillary features such as a distinctive arching of the anterior alveolar processes of the premaxillae, a peculiar arrangement of the first two premaxillary alveoli and a large size disparity between the 3rd and 4th premaxillary alveoli. These features presently allow formal recognition of two species within the genus, Paludirex vincenti and Paludirex gracilis comb. nov., with the former having comparatively more robust rostral proportions than the latter. The Paludirex vincenti holotype comes from the Pliocene Chinchilla Sand of the Darling Downs, south-eastern Queensland, whereas the material assigned to Paludirex gracilis is from the Pleistocene of Terrace Site Local Fauna, Riversleigh, northwest Queensland. Phylogenetic analyses recover Paludirex vincenti as a mekosuchine, although further cladistic assessments are needed to better understand the relationships within the clade.

Paludirex vincenti roamed Earth during the Pliocene epoch, between 5 and 2.5 million years ago. Nicknamed the ‘swamp king,’ it grew up to 5 m (16.4 feet) long and was capable of preying on giant prehistoric marsupials. “Crocs have been an important component of Australia’s fauna for millions of years,” said senior author Dr. Steve Salisbury, a paleontologist in the School of Biological Sciences at the University of Queensland, Brisbane. “But the two species we have today — Crocodylus porosus and Crocodylus johnstoni — are only recent arrivals, and were not part of the endemic croc fauna that existed here from about 55 million years ago.” “Whether Paludirex vincenti went extinct as a result of competition with species like Crocodylus porosus is hard to say.” “The alternative is that it went extinct as the climate dried, and the river systems it once inhabited contracted — we’re currently investigating both scenarios.” Several fossilized specimens of Paludirex vincenti were discovered near the town of Chinchilla in south-eastern Queensland. “The largest crocodylian today is the Indo-Pacific crocodile, Crocodylus porosus, which grows to about the same size,” said lead author Jorgo Ristevski, a Ph.D. candidate in the School of Biological Sciences at the University of Queensland, Brisbane. “But Paludirex vincenti had a broader, more heavy-set skull so it would’ve resembled an Indo-Pacific crocodile on steroids.”

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