Meeting Abstract
Crocodylian snout shape, the region of the skull in front of the eyes, is tightly linked with dietary ecology. Some species, like Tomistoma schlegelii, have incredibly elongated snouts while others, like Osteolaemus tetraspis, have short, wide snouts. Although species form a continuum between these extremes, little is known about the developmental processes that determine differences in snout length. Prior study of Alligator mississippiensis revealed early facial proliferation is distributed throughout the snout and, unlike birds, is not constrained to an apical growth zone. Later stages with well defined cranial cartilages lack obvious growth plates, similar to post-hatching Anole lizards. To study how snout shape differences arise, we injected EdU in ovo to quantify proliferation at key developmental stages in three species with different snout lengths (A. mississippiensis, O. tetraspis, and T. schlegelii). This marker, in concert with histological staining, allowed us to test whether differences in the rate of cellular proliferation are apparent from the start of facial elongation or if differences in length are related to how long proliferation is maintained during snout morphogenesis. Although differences in facial shape are distinct as early as Ferguson stage 17, patterns of proliferation at earlier stages are not. Our data suggest a model wherein proliferation rate decreases earlier in blunt species than slender species. Genes which modulate proliferation are, therefore, ideal targets for future studies of developmental mechanisms for the evolution of crocodylian cranial diversity.
