Endocranial morphology of psittacosaurs (Dinosauria: Ceratopsia) based on CT scans of new fossils from the Lower Cretaceous, China

Abstract

Psittacosaurs, small basal ceratopsians with a parrot-like beak, are among the most abundant dinosaurs, but occur only in the Early Cretaceous of East Asia. Although the general morphology of psittacosaurs is fairly well understood, the endocranial anatomy of the group has never been described. New discoveries of well-preserved skulls from the celebrated Liaoning beds in northeastern China provide the material for conducting research on psittacosaur endocranial morphology. Using computed tomography scans of three-dimensionally preserved skulls, this study reveals basic endocranial anatomy of psittacosaurs and provides the first palaeoneurological evidence of psittacosaurs in relation to their behaviour. Although commonly believed to have had a small brain and small eyes, psittacosaurs had relatively high brain/body size ratios that are comparable to those in the large theropod Tyrannosaurus, and probably had a keen sense of smell and acute vision, as evidenced by their enlarged olfactory lobes and bulbous optic lobes. The configuration of the semicircular canals agrees with limb proportions to suggest that psittacosaurs were agile animals, perhaps better able to escape predation by carnivorous dinosaurs on that account. The behavioural adaptations implied by this study may have been crucial for the successful radiation of psittacosaurs during the Early Cretaceous of East Asia.