Mechanistic Thermal Modeling of Late Triassic Terrestrial Amniotes Predicts Biogeographic Distribution

Abstract

The biogeography of terrestrial amniotes is controlled by historical contingency interacting with paleoclimate, morphology and physiological constraints to dispersal. Thermal tolerance is the intersection between organismal requirements and climate conditions which constrains modern organisms to specific locations and was likely a major control on ancient tetrapods. Here, we test the extent of controls exerted by thermal tolerance on the biogeography of 13 Late Triassic tetrapods using a mechanistic modeling program, Niche Mapper. This program accounts for heat and mass transfer into and out of organisms within microclimates. We model our 13 tetrapods in four different climates (cool and warm at low and high latitudes) using environmental conditions that are set using geochemical proxy-based general circulation models. Organismal conditions for the taxa are from proxy-based physiological values and phylogenetic bracketing. We find that thermal tolerances are a sufficient predictor for the latitudinal distribution of our 13 test taxa in the Late Triassic. Our modeled small mammaliamorph can persist at high latitudes with nocturnal activity and daytime burrowing but large pseudosuchians are excluded because they cannot seek nighttime shelter in burrows to retain elevated body temperatures. Our work demonstrates physiological modeling is useful for quantitative testing of the thermal exclusion hypothesis for tetrapods in deep time.