Ontogeny of the Massospondylus labyrinth: implications for locomotory shifts in a basal sauropodomorph dinosaur

Ontogeny is a vital aspect of life history sometimes overlooked in palaeontological studies. However, the changing geometry of anatomical structures during growth can be informative regarding ecological and functional reconstructions. The inner ear, or labyrinth, is an ideal ontogenetic study system because it has a strong functional signal in its morphology that is linked to locomotor mode. Yet almost nothing is known about labyrinth development in dinosaurs. We quantified labyrinth scale and geometry through ontogeny in the Early Jurassic dinosaur Massospondylus carinatus, which has an exceptional fossil record and is hypothesized to have undergone a gait change, from quadrupedal juvenile to bipedal adult. To test whether this putative locomotor shift is reflected in labyrinth morphology, computed microtomography (μCT) and propagation phase‐contrast synchrotron radiation microtomography (PPC‐SRμCT) were used to obtain labyrinths from eight specimens, ranging from near‐hatchling to adu...个体发育（Ontogeny）是生物生活史的核心组成部分，却常为古生物学研究所忽视。生物体生长过程中解剖结构的几何形态变化，可为生态与功能重建提供关键依据。内耳（或称迷路）是个体发育研究的理想对象：其形态蕴含显著的功能信号，且与运动模式密切相关。然而学界对恐龙内耳迷路的发育过程几乎一无所知。本研究以早侏罗世恐龙大椎龙（Massospondylus carinatus）为研究对象——该类群拥有极为完整的化石记录，且被推测存在步态转变：幼体以四足行走，成体转为两足行走——我们量化了其个体发育全程中内耳迷路的尺度与几何形态。为验证这一推测的运动模式转变是否在内耳迷路形态上有所体现，本研究采用显微CT（computed microtomography，μCT）与传播相位衬度同步辐射显微CT（PPC-SRμCT），对8件涵盖从近孵化幼体至成体各发育阶段的标本进行扫描，获取了其内耳迷路数据。