Meeting Abstract

P3.148  Monday, Jan. 6 15:30  Quantifying the Relationship Between Curvature and Sheath Length in Bird Claws NOTO, C.R.*; ZANNO, L.E.; WITYNSKI, D.; MEYER, K.; University of Wisconsin-Parkside, Kenosha; North Carolina Museum of Natural Sciences, N.C. State Univ., Raleigh; University of Wisconsin-Parkside; University of Wisconsin-Parkside noto@uwp.edu

Many studies have related the claw geometry of birds (size, curvature, etc.) to ecology with varying success. However, to date, ecomorphological correlations have considered the morphology of the whole claw, without attention to the bone core component. Tetrapod unguals (claws) are composite structures formed from an internal bone core and superficial keratinous sheath. It is assumed that the distal extension of the keratinous sheath beyond the bone core remains constant across claw morphologies, yet this has not been measured empirically. Here we present results from a dataset consisting of 200+ specimens from 150 taxa representing most major bird orders. Claw images were captured in lateral view using a custom-built, high resolution, digital X-ray unit. Bone core radius (core length), whole claw radius (claw length), and bone core angle (core angle) were measured using the software ImageJ. The proportion of the claw length made up by the core length was calculated to remove the effect of size. Results indicate that the contribution of the sheath to total claw length varies with the bone core curvature. As the core angle decreases (becomes more trenchant), the proportion of the total claw length made up by the keratinous sheath decreases. This relationship spans all bird orders tested, yet varies in strength across clades. We suggest that this relationship has both biomechanical and phylogenetic components warranting further study. Characterizing core/sheath relationships in birds is an important tool for identifying ecomorphological relationships in extinct theropod dinosaurs and a first step toward extending these patterns to tetrapods in deep time.