68.5 Friday, Jan. 6 Ontogeny and Modularity in the Crocodilian Skull JASZLICS, A.*; PARDO, J. D.; University of Texas at Arlington email@example.com
Variation in ontogenetic trajectories plays a critical role in shaping morphological diversity of the vertebrate skull. Crocodilians are a potentially informative group in which to study this phenomenon because they demonstrate a relatively large degree of morphological diversity in the skull, in spite of a relatively high degree of ecological and phylogenetic constraint. Previous studies of crocodilian skull morphology have shown that the majority of extant species occupy a contiguous morphospace, with the exception of the Indian gharial, Gavialis gangeticus. These studies demonstrate that variation in morphology largely reflects biomechanical constraint during feeding. In order to test whether the diversity of crocodilian skull morphologies is achieved through dissociation of ontogenetic modules, we sampled growth sequences representing each of the four major extant lineages (Alligatoridae, Crocodylidae, Tomistominae and Gavialinae). We then used a geometric morphometrics-based approach to compare ontogenetic trajectories in these taxa. Principle components analyses show a tight integration of the entire skull, specifically between rostral length and the width of the suspensorium relative to the braincase in crocodylids, alligatorids and tomistomines. Gavialines however, show a strong disintegration of the suspensory module from the rostrum. We hypothesize that this dissociation is the result of the slender rostrum and 'snapping' feeding mechanism of true gharials, which places unique constraints on adductor morphology. This suggests that variation along even highly constrained ontogenetic trajectories can produce diverse morphologies.