Ontogenetic dietary partitioning in a Triassic sauropterygian: implications from a new juvenile specimen of Brevicaudosaurus jiyangshanensis (Reptilia: Diapsida)

During the first 10 million years of the Triassic, sauropterygians diversified rapidly into a variety of marine predatory niches. Adults of the late Middle Triassic eosauropterygian Brevicaudosaurus jiyangshanensis from southern China exhibit fang-shaped premaxillary teeth that resemble those of some nothosaurids and are adapted for feeding on large prey. Here, we report a juvenile example of the species, about one-third the length of the adult. The new juvenile shares apomorphies of the adult, like the posteriorly constricted parietal table, broadened humeral mid-diaphysis and short tail. However, its juvenile status is confirmed by unfused contralateral neural arch halves and developing epiphyses of the humerus. The small, smooth, conical premaxillary teeth of the juvenile differ from the ornamented fangs of the adult. The differences in the tooth morphology between the juvenile and adult suggest that this is an example of ontogenetic dietary niche partitioning, a common strategy for reducing intraspecific competition.