A morphometric analysis of the autopodia of the American crocodile (Crocodylus acutus) in Costa Rica

Cory J Kumagai, Purdue University

Abstract

In a fossil footprint assemblage, identifying and assigning foot prints to a track maker becomes increasingly difficult with increases in morphological similarity. This problem occurs fairly regularly when regarding archosaurian footprints, with several groups of animals sharing similar autopodial (hand [manus] and foot [pes])) morphologies when they may not be particularly closely related. Among the research of trace fossils, there is a study (Olsen, 1980; Olsen et al. 1998) of a purported growth series for a range of tracks spanning three ichnogenera; thus suggesting the three ichnogenera may actually be one, with the differences in shape attributed to ontogeny. The purpose of this study is to analyze the shape of the autopodia of an extant archosaur, Crocodylus acutus, to analyze the extent of ontogenetic shape change that occurs, intraspecifically. Reduced major axis and principal components analysis (PCA) were used primarily to assess changes in several proportions of the manus, pes, body, and limb lengths. Test scenarios were run in both bivariate and multivariate comparisons. Comparing the manus and pes with body and limb lengths, both bivariate and multivariate analyses indicate slight negative allometry. Bivariate, multivariate, and PCA comparisons of intra-manus or intra-pes parameters indicated that the length proportions grow isometrically. Scaled digit parameters were also made by subtracting a multivariate size factor from the manus or pes parameter to graphically analyze shape change without size as a factor. These graphs also indicate that there is not very much change in length proportions as the animal increases with size. Collectively these results suggest there is not a significant degree of change in foot proportions, and the degree of change observed in the footprint series in Olsen 1980 is more likely to be due to the prints being made by several species, rather than being representative of one species over a growth series

Degree

M.S.

Advisors

Paladino, Purdue University.

Subject Area

Morphology|Paleontology|Latin American Studies

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