Multivariate analysis of avian and non-avian theropod pedal phalanges

Abstract

The relationship between morphology and behavior in theropods was examined using multivariate analyses performed on a set of linear measurements of pedal non-ungual phalanges in a sample of 132 extant and 13 extinct taxa. Principal component analysis reveals that modern birds with terrestrial lifestyles tend to cluster away from those with raptorial and non-predatory grasping lifestyles although the division is not clean. Most non-avian dinosaurs tend to cluster with terrestrial species although Deinonychus and some Tyrannosaurids cluster with raptorial taxa. Terrestrial taxa tend to have phalanges that are comparatively shorter distally, are relatively wide, and have shallow grooving of the distal trochleae, while grasping taxa show opposing trends. Predatory graspers have proportionately wider phalanges than non-predatory graspers. Discriminant function analysis performs well in distinguishing among species with specialized behavior while taxa with less stereotyped behaviors are harder to classify. Predatory graspers are easily separated from non-predatory graspers. Troodon and Elmisaurus are grouped with terrestrial/cursorial taxa. Tyrannosaurus, Allosaurus, Daspletosaurus, and Albertosaurus are identified as terrestrial/cursorial with some possible predatory grasping ability. Deinonychus and Bambiraptor appear to have more grasping ability than Troodon.