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PeerJ. 2019 Aug 14;7:e7217. doi: 10.7717/peerj.7217. eCollection 2019.

Ontogenetic braincase development in Psittacosaurus lujiatunensis (Dinosauria: Ceratopsia) using micro-computed tomography.

Author information

School of Earth Sciences, University of Bristol, Bristol, UK.
Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing, China.
Department of Earth Sciences, Carleton University, Ottawa, ON, Canada.
Contributed equally


Ontogenetic sequences are relatively rare among dinosaurs, with Ceratopsia being one of the better represented clades, and especially among geologically earlier forms, such as Psittacosaurus. Psittacosaurus is a small, bipedal basal ceratopsian abundant in the Lower Cretaceous deposits of Asia, whose cranial and endocranial morphology has been well studied, but only cursory details have been published on the bones surrounding the brain. Using reconstructions created from micro-computed tomography scans of well-preserved skulls from the Barremian-Aptian Yixian Formation, China, we document morphological changes in the braincase of Psittacosaurus lujiatunensis through three growth stages, hatchling, juvenile, and adult, thus providing the first detailed study of ceratopsian braincase morphology through ontogeny. Notable ontogenetic changes in the braincase of P. lujiatunensis include a dramatic relative reduction in size of the supraoccipital, an increase in the lateral expansion of the paroccipital processes and a decrease in the angle between the lateral semicircular canal and the palatal plane. These ontogenetic morphological changes in the braincase relate to expansion of the cranium and brain through growth, as well as reflecting the switch from quadrupedal juveniles to bipedal adults as documented in the changing orientation of the horizontal semicircular canal through ontogeny. Recognition of these patterns in a basal ceratopsian has implications for understanding key events in later ceratopsian evolution, such as the development of the parieto-squamosal frill in derived neoceratopsians.


Braincase; Ceratopsian; Dinosaurs; Morphology; Ontogeny; Psittacosaurus; Tomography

Conflict of interest statement

The authors declare that they have no competing interests.

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