Femoral ontogeny and locomotor biomechanics of Dryosaurus lettowvorbecki (Dinosauria, Iguanodontia)

Femoral ontogeny in the iguanodontian dinosaur Dryosaurus lettowvorbecki (Late Jurassic, Tanzania) is analysed biomechanically using principles of beam theory. Statistically significant differences in cross-sectional properties are found between animals of differing size, reflecting alterations to both the relative amount and distribution of cortical bone during growth. Two explanations are suggested to account for these modifications in bone architecture: (1) increasing mechanical loads related to increasing body size, and (2) changes in the orientation of these loadings associated with a caudal shift of the centre of gravity. It is argued that D. lettowvorbecki hatchlings were not bipedal as generally presumed but obligate quadrupeds. Based on avian growth rates, the transition from quadrupedality to habitual bipedalism is estimated to have occurred within several months of hatching. The biomechanical approach employed here contributes new insight into ontogeny of locomotion in D. lettowvorbecki and provides additional ways of analysing ontogenetic processes among extinct and living species.