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

Abstract

<p>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 <i>Crocodylus</i>, 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 mekosu-chines, 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 extinctcrocodylians. 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 major-ity of mekosuchines outside of Longirostres and the Late Cretaceous–early Paleogene Oriental osuchina 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.</p>