Long bone scaling and limb posture in non-avian theropods: Evidence for differential allometry

ABSTRACT

Long bone allometry has been analyzed in a large sample of non-avian theropod dinosaurs spanning almost the entire size range of known adult species. Theropod long bone allometry closely parallels the trends observed in extant mammals. Like mammals, large theropods scale with significantly lower regression slopes than do smaller species. As in extant mammals non-avian theropods are neither geometrically nor elastically similar. Large non-avian theropods tend to be elastically similar, whereas small species approach geometric similarity. As in extant mammals non-avian theropods appear to show a size dependent change in limb posture, aligning the individual long bones more steeply to vertical with increasing size, thus probably reducing the mass specific amount of force necessary to counteract moments about the joints. The main difference between non-avian theropods and mammals appears to be the retention of very long limbs among large non-avian theropod species, which, however, is not unparalleled among extant large mammals.