Meeting Abstract
Crocodylian skull shape is tightly associated with dietary ecology. A continuum of snout lengths exists in living crocodylians, from short & blunt faces in the dwarf crocodile (Osteolaemus tetraspis) to dramatically elongated snouts in the tomistoma (Tomistoma schlegelii). The evolution and function of snout shape has been widely explored, but the developmental programs which underlie differences in snout length have yet to be revealed. Comparative developmental studies in birds and mammals (e.g., Darwin’s finches and bats) have revealed facial elongation can be achieved by maintaining or increasing the rate of cell proliferation in the facial mesenchyme and/or delaying skeletal differentiation. Our previous work showed heterochrony was critical in the evolution of crocodylian skull ontogeny. We now aim to study cellular dynamics (cell proliferation and cycling) and gene expression at key developmental stages in three species with distinct snout lengths: Alligator mississippiensis, O. tetraspis, and T. schlegelii. Integrating in ovo EdU labeling with in situ hybridization allows us to assess if temporal and spatial shifts in the expression of genes controlling skeletogenesis can explain differences in cranial ontogeny. Our data show differences in proliferation rate at the tip of the snout can be detected at Ferguson stage 14, prior to differences in facial length. Our results so far suggest cell proliferation decreases earlier in the blunt-snouted species than species with longer faces and may be driven by differential deployment of genes controlling cartilage differentiation (e.g., Bmp4 or CaM).
