Barrett, P. & Zhao, Q. (2006) Evidence for post-nestling gregarious behaviour in the basal Ceratopsian dinosaur Psittacosaurus. JVP 26(3) Abstracts pp.40

Elaborate cranial ornamentation (horns, frills) and evidence from paucispecific bonebeds indicate that many neoceratopsian dinosaurs had complex social behaviours, including living in herds and intraspecific display. However, many of these features are unknown or poorly developed in basal ceratopsians, which have relatively unadorned skulls and do not occur in bonebeds.

Here, we report an exceptionally preserved group of the basal ceratopsian dinosaur Psittacosaurus from the Lujiatun Beds of the Yixian Formation (Barremian: Lower Cretaceous) in Liaoning, People’s Republic of China. The specimen consists of six juvenile individuals that were apparently killed in a mass mortality event. All the individuals are oriented in the same direction and the skeletons are complete and articulated indicating that no post mortem transport occurred.

Developmental Mass Extrapolation permits reconstruction of the age profile of this group: the youngest individual was aged just over one year, while the oldest was just under three years old. This profile is consistent with the presence of individuals from several different clutches within the same group and suggests that Psittacosaurus lived in small stable herds including several age classes. We interpret this as the first evidence of post-nestling gregarious behaviour in a basal ceratopsian. This indicates that potentially complex social behaviours emerged early in the evolutionary history of the clade and preceded the appearance of the spectacular cranial ornamentation that characterises neoceratopsians.

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