Abstract

Growth characteristics are observed in Psittacosaurus mongoliensis. A taxonomic overview of the fossil remains of psittacosaurs suggests that there is one well-established genus, Psittacosaurus, with two well-established species, P. mongoliensis and P. sinensis. Two new species from the Lower Cretaceous of China have been discovered recently and their diagnostic characters are summarized.

Introduction

Parrot-beaked dinosaurs were first discovered in Lower Cretaceous strata of the Gobi Desert in 1922, and represent the first relatively complete skeletons uncovered by the famous Central Asiatic Expeditions of the American Museum of Natural History. The following year, Osborn (1923) established two new species, Psittacosaurus mongoliensis and Protiguanodon mongoliense, on the basis of two complete skeletons. Despite subsequent recovery of significant new materials pertaining to psittacosaurs and their bearing on the phylogenetic position of the Ceratopsia, no thorough systematic account is currently available.

In anticipation of a formal systematic review, I present a systematic survey of psittacosaur species including a report on the discovery of two new species. I also briefly discuss the phylogenetic affinity of psittacosaurs.

Growth characteristics in Psittacosaurus mongoliensis

Several growth stages are available for Psittacosaurus mongoliensis that provide important information regarding character change during ontogeny. The smallest individual is a hatchling (AMNH 6535), the cranium of which has received preliminary treatment by Coombs (1980, 1982). Recently, the lower jaws and partial postcranium of the same individual have been located and reassociated with the cranium.