Geometric morphometrics of Antillean Crocodiles

Geometric morphometrics commonly have been utilized to explore patterns of variation across a wide range of taxa. We present a geometric morphometric analysis of skull shape morphology for New World crocodilians of the genus Crocodylus, placing emphasis on studying variation within the Greater Antillean region of the Neotropics. It has been suggested that the major factor contributing to the modern diversity of Cuban (C. rhombifer) and American crocodiles (C. acutus) in the Greater Antilles is the result of ancient hybridization. Genetic studies found that mitochondrial DNA haplotypes for C. acutus in the Greater Antilles are actually more closely related to C. rhombifer than other American crocodiles throughout the Neotropics. To infer whether genetic relationships are correlated with morphological relationships, we use geometric morphometrics to assess shape variation and compare skull morphology to a reconstruction of a cytochrome-b gene phylogeny. Analysis of skull shape variation using geometric morphometrics of landmark data reveals three broad groups of New World Crocodylus within the given morphospace. Two of these groups correspond to present day Crocodylus whereas the other corresponds to fossil specimens of C. rhombifer. Within these groups, nearly all sub-groups correspond to our current taxonomic understanding of New World Crocodylus; except for the placement of Greater Antillean C. acutus, which clusters much closer to C. rhombifer. This further supports recent studies of Greater Antillean C. acutus dynamics and their genetic phylogenies, indicating a unique evolutionary history.