Abstract
Spatial incompleteness in the fossil record severely diminishes the observed ecological and geographic ranges of clades. The biological processes shaping species distributions and richness through time, however, also operate across geographic space and so clade biogeographic histories can indicate where their lineages must have successfully dispersed through these sampling gaps. Consequently, these histories are powerful, yet untapped tools for quantifying their unobserved ecographic diversity. Here, we couple phylogeographic modelling with a landscape connectivity approach to reconstruct the origins and dispersal of Permian-Triassic archosauromorph reptiles. We recover substantial ecographic diversity from the gaps in their fossil record, illuminating the cryptic first 20 million years of their evolutionary history, a peak in climatic disparity in the earliest Triassic period, and dispersals through the Pangaean tropical dead zone which contradict its perception as a hard barrier to vertebrate movement. This remarkable tolerance of climatic adversity was probably integral to their later evolutionary success.