Meeting Abstract

67.4  Monday, Jan. 6 08:45  Implications of Morphological Variation in the Manual Unguals of Theropod Dinosaurs NOTO, C.R.; University of Wisconsin-Parkside, Kenosha noto@uwp.edu

Among living tetrapods, research shows a strong correlation between claw shape and such factors as locomotor mode or predatory behavior. Using a similar approach to dinosaur unguals we may expect that differences in claw shape will follow ecological and/or evolutionary patterns. Theropod manual unguals vary greatly in overall morphology (size, length, curvature), yet their shape has not been studied in detail. A geometric morphometric analysis was applied to images of 200 claws, representing over 80 theropod taxa, including early birds. Results of principal components analysis (PCA) show that most shape variation occurs in two areas: the degree of nail curvature and nail size relative to the ungual body. Statistical analysis between theropod clades shows coelurosaurs fill a much larger proportion of shape space than non-coelurosaurs suggesting greater ecological diversification. The claws of non-coelurosaurs appear exclusively predatory in function, likely being used as giant hooks or gaffes to hold prey. Within different coelurosaur clades, the evolution of ecological specializations is recorded in changing claw shape as one moves toward derived members of a group, for example the evolution of elongated, straight claws in herbivorous ornithomimids. The claw shape of some small paravians (including birds) falls outside other groups and may represent a specialization for climbing. This novel approach allows one to explore ecological differences between theropod species and higher taxa, including food preference and predatory behavior, though correlating specific behaviors with claw shapes may be premature at this time. Furthermore, these results may aid in understanding the evolution of the theropod manus, its functional changes, and yield important character data useful for cladistic analyses.