For a while, crocodile: crocodylomorph resilience to mass extinctions

Crocodylomorphs are the sole survivors of the pseudosuchian clade and have, thus far, endured two mass extinctions. Despite being stereotyped as “living fossils”, the characteristics that facilitated their survival remain largely unknown, but trends in other clades, such as mammals, suggest that dietary ecology may play a key role in persisting during and after mass extinctions. To test the role of dietary ecology in the survival of crocodylomorphs, we use geometric and linear morphometrics to quantify the cranial shape of crocodylomorphs through the Mesozoic and into the Cenozoic. We then compare these data to living amniotes and combine these results with additional morphological proxies, which together permit the reconstruction of dietary ecology. We find that crocodylomorph cranial morphology exhibits a greater disparity during much of the Mesozoic than today. Many extinct crocodylomorphs express morphologies that overlap with extant crocodylians and lepidosaurs, indicating a diverse range of diets, but convergence with extant mammals is exceptionally rare. Numerous crocodylomorphs from across geologic time and phylogeny span a range of morphospace not occupied by sampled extant amniotes. Using these data, we suggest that a generalist dietary ecology is associated with mass extinction survivors, a trend previously observed in other clades, such as mammals. Terrestrial generalists appear to survive and diversify following the end-Triassic mass extinction, whereas semiaquatic generalists persist through the end-Cretaceous mass extinction. We propose that one reason for the success and longevity of the crocodylomorph clade is their remarkable dietary flexibility, a characteristic that is still observed in living crocodylians.

Methods
Photography of skulls in dorsal and lateral view, as well as raw landmark data derived from ImageJ.