THE ONTOGENY OF PTERANODON AND OTHER PTEROSAURS

Immature specimens of the Late Cretaceous pterosaur Pteranodon were identified using three size-independent criteria: (1) fusion of various cranial and postcranial elements; (2) degree of epiphyseal ossification; and (3) bone grain or degree of ossification of limb-bone shafts. Immature individuals make up 15% of available specimens of Pteranodon and do not differ significantly in size from mature individuals. This and the extensive fusion of the mature skeleton suggest that Pteranodon had determinate growth. The bone of limb-bone shafts of immature individuals is fibro-lamellar bone, which suggests that they grew rapidly to adult size. The size-independent criteria can also be used to identify immature and mature individuals of other pterosaur taxa, and other large pterodactyloids also probably exhibited rapid determinate growth.