Migrations, diversifications and extinctions: the evolutionary history of crocodyliforms in Australasia

Abstract

Crocodyliform palaeontology in Australasia has a productive research record that began in the late nineteenth century and continues today. In this study, we summarize the current understanding on the taxonomic diversity and phylogenetic relationships of Australasian crocodyliforms based on first-hand knowledge of relevant fossil material and a review of the published literature. The currently known fossil record of Crocodyliformes in Australasia spans more than 113 million years, from the Early Cretaceous to the Holocene, and largely consists of body fossils discovered on continental Australia. Whilst only two crocodyliform genera are recognized from Australasia’s Mesozoic, the Cenozoic is distinguished by a remarkable taxonomic diversity of crocodylian crocodyliforms. By far the most common crocodylians from Australasia are members of Mekosuchinae, whose fossils are unambiguously known from the early Eocene until the Holocene. In addition to mekosuchines, during the Cenozoic Australasia was also inhabited by gavialoids and species of Crocodylus, with four extant species of the latter being the only surviving crocodylians in Australia and New Guinea. The phylogenetic relationships of Australasia’s crocodylians, particularly mekosuchines, have been a topic of interest to palaeontologists for over two decades. We performed several phylogenetic analyses to test the relationships of Mekosuchinae and other extinct crocodylians. Most results from our analyses found Mekosuchinae as a basal crocodyloid clade within Longirostres. However, some of the results recovered an alternative position for the majority of mekosuchines outside of Longirostres and the Late Cretaceous–early Paleogene Orientalosuchina as its deeply nested subclade. These results suggest that Mekosuchinae had its origins in Asia during the Cretaceous, and that mekosuchines arrived from southeast Asia into Australia no later than the late Paleocene. If this hypothesis is correct, then Mekosuchinae would no longer be an Australasian endemic clade since mekosuchines also seem to have persisted on continental Asia until the late Eocene.Jorgo Ristevski [jorgo.ristevski@gmail.com], School of Biological Sciences, The University of Queensland, Brisbane, 4072, Queensland, Australia; Paul M. A. Willis [paul@palaeopictures.com], School of Biological Sciences, Flinders University, Adelaide, 2100, South Australia, Australia; Adam M. Yates [Adamm.Yates@magnt.net.au], Museum of Central Australia, Museum and Art Gallery of the Northern Territory, Alice Springs, 0870, Northern Territory, Australia; Matt A. White [fossilised@hotmail.com], Palaeoscience Research Centre, University of New England, Armidale, 2351, New South Wales, Australia, Australian Age of Dinosaurs Museum of Natural History, The Jump-Up, Winton, 4735, Queensland, Australia; Lachlan J. Hart [l.hart@unsw.edu.au], Earth and Sustainability Science Research Centre, School of Biological, Earth and Environmental Sciences (BEES), University of New South Wales, Kensington, 2052, New South Wales, Australia, Australian Museum Research Institute, 1 William Street, Sydney, 2010, New South Wales, Australia; Michael D. Stein [michael.stein@unswalumni.com], Earth and Sustainability Science Research Center, School of Biological, Earth and Environmental Sciences (BEES), University of New South Wales, Kensington, 2052, New South Wales, Australia; Gilbert J. Price [g.price1@uq.edu.au], School of Earth and Environmental Sciences, The University of Queensland, Brisbane, 4072, Queensland, Australia; Steven W. Salisbury [s.salisbury@uq.edu.au], School of Biological Sciences, The University of Queensland, Brisbane, 4072, Queensland, Australia.