Meeting Abstract

51.11  Saturday, Jan. 5  Morphometrics of Crocodilian Cranial Variation in Ecomorphology and Ontogeny SADLEIR, R.W.; Univ. of Chicago and the Field Museum, Chicago, IL rsadleir@uchicago.edu

Crown group crocodilians exhibit a high degree of cranial shape variation and convergence throughout their 80 million-year fossil record. Phylogenetic character correlation tests show that repeated transitions among generalized, blunt and slender cranial ecomorphotypes may mislead crocodilian systematics by influencing phylogenetic character-state transitions. Further investigation of ecomorph-character correlations is limited by the undetermined accuracy of current ecomorph definitions and unexplored ontogenetic relationships among existing ecomorphs. Using three-dimensional landmark-based geometric morphometric methods, cranial shape variation in extant and fossil crocodilians is analyzed to test whether existing cranial ecomorph classifications accurately reflect quantified cranial shape variation, and if like ecomorph taxa have identical ontogenetic shape-change trajectories. 120 landmarks summarizing crocodilian cranial shape in dorsal and ventral perspectives have been collected from over 200 specimens representing the ontogenies of 21 extant crocodilians and select fossil taxa. Cranial shape distributions within an empirical morphospace reveal greater skull shape diversity than is currently recognized. Blunt cranial ecomorphs do not display the taxonomic divisions observed among slender and generalized taxa, and with systematic correlation results, suggest that blunt ecomorphs obfuscate phylogenetic resolution. Analysis of ontogenetic shape change shows that taxa with the same static cranial ecomorphotype can possess different ontogenetic trajectories. Furthermore, differences in environmental conditions for Alligator mississippiensis (i.e. farmed vs. wild) are found to alter skull shape to a scale transcending species shape-boundaries.