Bertozzo Filippo, Kecheng Niu, Gillette Nathan Vallée, Godefroit Pascal
Institute of Natural Sciences, Brussels, Belgium.
Sociedade de Historia Natural, Torres Vedras, Portugal.
PLoS One. 2025 Jan 24;20(1):e0312519. doi: 10.1371/journal.pone.0312519. eCollection 2025.
Ornithopod dinosaurs appeared during the Middle Jurassic, but it was in the Lower Cretaceous they started their successful evolutionary history. Different phylogenies describing the evolutionary relationships of Ornithopoda are mostly based on cranial features, however there is a lack of well-preserved and complete skulls for the basal member of the clade, hampering our knowledge on the mode and tempo of these herbivorous dinosaurs. Here we describe YLSNHM 01942, a well-preserved skull of a juvenile neornithischian from the Liaoning Province of China. The specimen was scanned with a μCT scan, and all the elements were segmented and extrapolated for description. The specimen shows a ventral deformation due to the compression of the sediment, and a few rostral elements were artificially added. The specimen is attributed to the basal ornithopod Jeholosaurus shangyuanensis because of the presence of a large foramen in the quadratojugal, however it lacks the nodular ornamentation on the postorbital and jugal, herein interpreted as an ontogenetic feature. This, together with the disarticulation degree of the cranial elements, suggest YLSNHM 01942 represents a juvenile Jeholosaurus. The endosseous labyrinth is tentatively reconstructed, although the disarticulation of the neurocranial bones hampers its complete reconstruction. Thanks to the analysis of previously undescribed inner neurocranial bones (such as the prootics, the exoccipital/ophistotic, basioccipital, and basisphenoid), we improve the previous phylogenetical scoring for J. shangyuanensis, and perform a phylogenetical analysis adding the basal ornithopod Changmiania liaoningensis and the recently re-evaluated Ajkaceratops kozmai. The phylogenetical analysis reports a well-supported base of Ornithopoda, with C. liaoningensis as the most basal ornithopod, and a resolved topology for Nanosaurus agilis, Changchunsaurus parvus, Haya griva, Yandusaurus hongheensis and J. shangyuanensis.
鸟脚亚目恐龙出现在中侏罗世，但直到下白垩世它们才开始了成功的进化历程。描述鸟脚亚目进化关系的不同系统发育树大多基于颅骨特征，然而，该类群基部成员保存完好且完整的头骨较为缺乏，这阻碍了我们对这些草食性恐龙的演化模式和速度的了解。在此，我们描述了YLSNHM 01942，这是一个来自中国辽宁省的保存完好的幼年新鸟臀目恐龙头骨。该标本进行了μCT扫描，所有骨骼元素都进行了分割和外推以进行描述。标本因沉积物挤压而出现腹侧变形，一些吻部骨骼元素是人工添加的。由于方轭骨上存在一个大孔，该标本被归入基部鸟脚亚目上园热河龙，但它缺乏眶后骨和颧骨上的结节状装饰，在此解释为个体发育特征。这一点，连同颅骨元素的分离程度，表明YLSNHM 01942代表一只幼年热河龙。尽管脑颅骨骼的分离阻碍了其完整重建，但仍初步重建了内耳迷路。得益于对先前未描述的脑颅内部骨骼（如耳前骨、枕外/耳后骨、基枕骨和基蝶骨）的分析，我们改进了之前对热河龙的系统发育评分，并进行了系统发育分析，加入了基部鸟脚亚目辽宁长面龙和最近重新评估的科氏阿克塞角龙。系统发育分析报告了一个得到充分支持的鸟脚亚目基部，辽宁长面龙是最基部的鸟脚亚目，并且解析了敏捷小恐龙、长春龙、哈雅格氏龙、红河盐都龙和热河龙的系统发育拓扑结构。
