Histology and postural change during the growth ofthe ceratopsian dinosaur Psittacosaurus lujiatunensis

摘要

A few dinosaurs are inferred to have undergone an ontogenetic shift from quadrupedal-tobipedalposture, or vice versa, based on skeletal allometry. The basal ceratopsianPsittacosaurus lujiatunensis is considered to have been mainly bipedal as an adult. Here weinfer a postural shift in this species based on a novel combination of limb measurements andhistological data. The forelimb is strongly negatively allometric relative to the hindlimb, andpatterns of vascular canal orientation provide evidence that growth of the hindlimb wasparticularly rapid during the middle part of ontogeny. Histology also makes it possible todetermine the ontogenetic ages of individual specimens, showing that the forelimb-tohindlimbratio changed rapidly during the first or second year of life and thereafter decreasedgradually. Occurrence of an ontogenetic shift from quadrupedality to bipedality was evidentlywidespread in dinosaurs, and may even represent the ancestral condition for the entire group.