Accounting for sampling heterogeneity suggests a low paleolatitude origin for dinosaurs

Abstract

Dinosaurs dominated Mesozoic terrestrial ecosystems for ∼160 million years, but their biogeographic origin remains poorly understood. The earliest unequivocal dinosaur fossils appear in the Carnian (∼230 Ma) of southern South America and Africa, leading most authors to propose southwestern Gondwana as the likely center of origin. However, the high taxonomic and morphological diversity of these earliest assemblages suggests a more ancient evolutionary history that is currently unsampled. Phylogenetic uncertainty at the base of Dinosauria, combined with the subsequent appearance of dinosaurs throughout Laurasia in their early evolutionary history, further complicates this picture. Here, we estimate the distribution of early dinosaurs and their archosaurian relatives under a phylogenetic maximum likelihood framework, testing alternative topological arrangements and incorporating potential abiotic barriers to dispersal into our biogeographic models. For the first time, we include spatiotemporal sampling heterogeneity in these models, which frequently supports a low-latitude Gondwanan origin for dinosaurs. These results are best supported when silesaurids are constrained as early-diverging ornithischians, which is likely because this topology accounts for the otherwise substantial ornithischian ghost lineage, explaining the group's absence from the fossil record prior to the Early Jurassic. Our results suggest that the archosaur radiation also took place within low-latitude Gondwana following the end-Permian extinction before lineages dispersed across Pangaea into ecologically and climatically distinct provinces during the Late Triassic. Mesozoic terrestrial vertebrates are under-sampled at low paleolatitudes, and our findings suggest that heterogeneous sampling has hitherto obscured the true paleobiogeographic origin of dinosaurs and their kin.