Climatic niche conservatism shapes the macroevolution, extinction, and survivorship of crocodile-line archosaurs

Abstract

Crocodylians are iconic thermophiles. Over 250 million years, crocodile-line archosaurs endured hyperthermals, climatic and range shifts, and two mass extinctions. Whether this niche conservatism reflects a deep evolutionary constraint or recent adaptation to novel climates remains unclear. We integrate present-day occurrences with a time-scaled phylogeny of >400 fossil and extant species. Niche models calibrated on living crocodylians were projected across 245 million years and compared with paleophylogeographic reconstructions. Macroevolutionary model fitting shows that temperature and precipitation exhibit strong phylogenetic structure, best described by bounded Ornstein-Uhlenbeck dynamics, indicating long-term niche conservatism. Poleward expansions in warm intervals and contractions in cool phases reflect tracking of conserved optima rather than niche evolution. Unlike non-avian dinosaurs, low-latitude suitability persisted across all but the most extreme end-Cretaceous scenarios, with recovery expanding from tropical refugia. Thermal and precipitation regimes shifted near the Cenomanian/Turonian hyperthermal (∼93.9 Ma) and Eocene/Oligocene aridification transition (∼33.9 Ma), respectively. Climatic niche conservatism is therefore ancient in crocodile-line archosaurs, but not completely static.