Bullar Claire M, Zhao Qi, Benton Michael J, Ryan Michael J
School of Earth Sciences, University of Bristol, Bristol, UK.
Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing, China.
PeerJ. 2019 Aug 14;7:e7217. doi: 10.7717/peerj.7217. eCollection 2019.
Ontogenetic sequences are relatively rare among dinosaurs, with Ceratopsia being one of the better represented clades, and especially among geologically earlier forms, such as . 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 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 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.
个体发育序列在恐龙中相对罕见，角龙类是其中代表性较好的类群之一，在地质年代较早的类群中尤为如此，比如……是一种小型两足基干角龙，在亚洲下白垩统地层中大量存在，其颅骨和脑颅形态已得到充分研究，但关于脑周骨骼的研究仅发表了一些粗略细节。利用对中国早白垩世巴列姆期—阿普特期义县组保存完好的头骨进行微计算机断层扫描所创建的重建模型，我们记录了……脑颅在幼体、 juvenile和成年三个生长阶段的形态变化，从而首次详细研究了角龙类脑颅形态的个体发育过程。……脑颅显著的个体发育变化包括枕上骨相对大小急剧减小、枕髁突横向扩展增加以及外侧半规管与腭平面夹角减小。脑颅的这些个体发育形态变化与生长过程中颅骨和脑的扩张有关，同时也反映了从幼年四足到成年两足的转变，这在个体发育过程中水平半规管方向的变化中得到了体现。在基干角龙类中识别出这些模式，对于理解后期角龙类进化中的关键事件具有启示意义，比如新角龙类中顶骨 - 鳞状骨褶边的发育。
