Cranial morphological variation in caiman (alligatoridae, caimaninae): morfogeometric study of the ontogeny of the species caimán latirostris and yacaré caiman

Abstract

We present the first study about the cranial disparity in C. yacare and C. latirostris using a two-dimensional geometric morphometric analysis. Skulls of different ontogenetic stages were photographed in dorsal and palatal views. For this study, 28 landmarks in dorsal view and 27 in palatal view were established and digitized using TPSUtil and TPSDig. MorphoJ was used for the analysis. To evaluate the change of shape in each species a regression with the landmarks coordinates against the logarithm of centroid size was performed. Ontogenetic trajectories were compared and a principal component analysis was done to identify the components of variation. Differences in ontogenetic trajectories were only observed in ventral view. The specimens were separated in relation to the first principal component. In dorsal view, in contrast with C. latirostris, C. yacare presents an elongated and narrow snout and skull, narrow orbits, a great concavity in the lateral margin of the skull at the level of the maxillar-jugal contact and a lower concavity of the rear edge of the cranial table. In ventral view, C. yacare presents an elongated and narrow skull, snout, pterygoid wings and suborbital fenestra and a medial displacement of the quadrate/quadrate-jugal contact and the anterolateral contact between maxillar and palatine.

Key words: Crocodylia, caimans, geometric morphometrics, skull, morphological disparity.