Growth curve of Psittacosaurus mongoliensis Osborn (Ceratopsia: Psittacosauridae) inferred from long bone histology

The skeleton undergoes substantial histological modification during ontogeny in association with longitudinal growth, shape changes, reproductive activity, and fatigue repair. This variation can hinder attempts to reconstruct life history attributes for individuals, particularly when only fossil materials are availble for study. Histological examinations of multiple elements throughout development provide a means to control for such variability and facilitate accurate life history assessments. In the present study, the microstructure of various major long bones of the ceratopsian Psittacosaurus monogoliensis Osborn were examined from a growth series spanning juvenile through adult developmental stages. The first reconstruction of a growth curve (mass vs. age) for a dinosaur was made for this taxon using a new method called Developmental Mass Extrapolation. The results suggest P. mongoliensis: (1) had an S-shaped growth curve characteristics of most extant vertebrates, and (2) had maximal growth rates that exceeded extant reptiles and marsupials, but were slower than most avian and eutherian taxa.