Meeting Abstract

P3.91  Sunday, Jan. 6  Pedal Digit IV Proportions Reveal Body-Size Associated Constraint on Dinosaur Foot Morphology LEARY, B; KAVANAGH, KD*; Univ. of Massachusetts Dartmouth; Univ. of Massachusetts Dartmouth kkavanagh@umassd.edu

The proportions of the pedal phalanges of tetrapods have been found to correlate with foot function. Plotting the phalangeal proportions of birds in morphospace not only allows us to discriminate functional groups, but also reveals a restricted range of variation in which many potential morphologies are unrepresented. Additionally, we observe some striking examples of convergent evolution. We observed that digit IV is effective in discriminating functional groups in birds. We applied this knowledge to the pedal phalanges of 30 non-avian theropods and bipedal ornithischians to identify functional groups and explore the range of variation in the ancestors of modern birds. Analyses revealed that (1) the phalanges proportions of all dinosaurs sampled fall within a subset of the range of variation observed in birds, (2) ornithischian dinosaurs fall exclusively within the range of terrestrial, non-perching birds (e.g. running, walking, swimming); exhibiting in most cases, extreme proximodistal gradient patterning, (3) non-avian theropods fall within a range spanning from terrestrial birds to highly arboreal taxa, but extreme raptorial morphologies are conspicuously absent (PCA) and (4) the phalanx proportions of non-avian theropods are strongly correlated with body length. We conclude that (1) the emergence of modern birds may have been preceded by a shift in pedal morphology to accommodate arboreal lifestyles, (2) the range of variation available to modern birds was also available to non-avian theropods, (3) non-avian theropods can be grouped into 2 distinct functional groups: terrestrial and arboreal, (4) while the ability to develop elongate distal phalanges exists in non-avian theropods, phalanx proportions may be constrained by larger body sizes.