THE EFFECT OF EPIPHYSEAL CARTILAGE LOSS IN BIRDS AND ITS IMPLICATIONS FOR DINOSAURS

The epiphysis is the uncalcified cartilage covering the ends of tetrapod long bones. Epiphyseal cartilage is primarily responsible for long axis growth and the shaping of the articular surfaces of long bones. Moreover, the movement and flexibility of limbs are influenced by the shape of the epiphyseal cartilage. In non-avian dinosaurs, an unknown amount of long bone shape and dimensions are lost during fossilization. To more accurately test hypotheses of dinosaur locomotion, we must first determine how much shape information is lost and where. I concluded an exploratory analysis of how the removal of epiphyseal cartilage in extant birds effects long bone shape and dimensions. The forelimbs and hindlimbs of domestic chickens (Gallus domesticus), ostrich chicks (Struthio camelus), and adult and juvenile Helmeted Guineafowl (Numida meleagris) were examined and measured before and after removal of their epiphyseal cartilage to determine what morphological changes occurred as a result. Not surprisingly, the humeri and femora of all examined juvenile birds contained a larger amount of epiphyseal cartilage than adult birds. Thus, after skeletonization, the shapes and sizes of lateral and medial condyles and the articular surfaces of the humeri and femora of juvenile birds were dramatically changed. Those of adult guineafowl, however, retained their overall size and shape. Significantly, there appears to be a correlation between locomotor activity and the shape of the underlying cartilage. The shape of the calcified cartilage more closely reflects the shape of the overlying cartilage in more physically active birds such as guineafowl. My results suggest that the shape of the preserved calcified cartilage in the weight-bearing elements of bipedal, non-avian dinosaurs (the hindlimbs) probably preserve more of the overlying epiphyseal cartilage shape than non-weight-bearing elements (the forelimbs).