BODY SIZE AND HABITAT EXTINCTION SELECTIVITY IN CROCODYLIFORMES

Crocodyliforms have a long and diverse evolutionary history, with members spanning terrestrial, semi-aquatic, and marine habitats and several orders of magnitude in body size. Habitat and body size have both been shown to be important factors in extinction risk throughout the geologic record. I used an existing body size and habitat database and a timescaled supertree to assess the relevance of these characteristics to the origination and extinction of Crocodyliform species since the Triassic. Analyses performed using BAMM reveal no uniform relationships between body size or habitat and extinction or origination rates across the phylogeny. Rather, the only deviation from broadly constant diversification rates across the tree was at the base of Thalattosuchia, one of the major marine clades, and further investigation suggests that this is not due to taxonomic or preservational biases. Logistic regressions at the stage level indicate minimal influence of body size or habitat on background extinction or origination. During the end-Jurassic, however, there was significant extinction selectivity against large species and extinction risk was higher for marine species than it was for non-marine species. Later, in the end-Cretaceous, there was significant extinction selectivity against small species and origination selectivity for large species. Further, extinction risk was higher for non-marine species than it was for marine species. These results indicate that body size and habitat were generally not important factors in extinction risk but played major roles in determining the survivors of these two major extinction events, ultimately producing the Crocodyliform diversity that remains today.