本文描述了中三叠世贵州兴义动物群中杨氏鸥龙的4件新化石材料并与前人报道的标本进行骨骼形态特征对比, 进一步修订了杨氏鸥龙的骨骼特征: 顶孔位于顶骨的一个凹槽内, 存在轭骨, 上颞孔长为眼眶长的2— 2.4倍, 间锁骨后未见后突等特征。同时, 从上述化石材料中识别出该属种的幼年期、亚成年期和成年期的个体发育特征: 成年期标本吻臀距＞1000 mm, 头骨的愈合程度更高, 肱骨发育内髁孔和外髁沟, 股骨近端收缩; 幼年期标本吻臀距＜500 mm, 头骨愈合程度和四肢骨化程度较弱, 肱骨无内髁孔和外髁沟, 股骨无收缩, 而亚成年期标本的骨骼介于两者之间。股骨的相对长度和肱骨末端的膨大程度可能与性别二态有关, 成年体的肱骨/股骨长度比值明显大于幼年体和亚成年体, 暗示杨氏鸥龙在个体发育过程中游泳能力增强, 海生形态生态适应加剧。

In this study, the key diagnostic characters of the Middle Triassic Lariosaurus youngi are re-evaluated based on comprehensive morphometric and osteological analyses of four newly discovered fossil specimens from the Xingyi fauna of Guizhou, together with previously described materials. The diagnostic characters reassessed include: (1) a pineal foramen positioned within a parietal trough; (2) the presence of a jugal; (3) an upper temporal fenestra with a longitudinal diameter 2 to 2.4 times that of the orbit; and (4) an interclavicle lacking a posterior stem. Ontogenetic stages of L. youngi—juvenile, subadult, and adult—are reconstructed. Adult individuals are characterized by a snout-vent length (SVL) exceeding 1000 mm and extensive skull fusion. Juvenile individuals (SVL ＜ 500 mm) exhibit reduced skull fusion, incomplete limb ossification, and comparatively simplified skeletal structures. Subadult individuals display intermediate morphological conditions, with skeletal features transitional between those of juveniles and adults. The relative lengths of the humerus and femur, along with the degree of epiphyseal expansion, may serve as reliable indicators of sexual dimorphism in L. youngi. Furthermore, the progressively higher humerus-to-femur length ratios observed from juveniles to adults suggest an ontogenetic enhancement of swimming capability.

国家重点研发计划项目(2023YFF0804000)、贵州省科技计划项目(黔科合平台ZSY[2024]002, [2021]一般463)和贵州省2024年新一轮找矿突破战略行动项目(安顺地区重点古生物化石保护及研究)联合资助