ABSTRACT

Bone histology has provided valuable information on the life history of dinosaurs, and the presence of growth lines provides useful information for age estimation, growth variation, and the reconstruction of paleobehavior. Here, we present new data recovered from five individuals of the non-iguanodontian ornithopod dinosaur Jeholosaurus shangyuanensis from the Early Cretaceous Jehol Biota. These specimens, ranging in body length from 16 to 62 cm, represent early juvenile, late juvenile, and subadult ontogenetic stages. The bones of Jeholosaurus mainly consist of fibrolamellar tissue, which is similar to that of other non-iguanodontian ornithopods; however, parallel-fibered bone and lamellar bone tissues were also deposited in early juvenile through subadult individuals, suggesting relatively slow growth rates. Parallel-fibered bone is only regionally present in the juvenile but is well developed throughout the outermost cortex of the subadult. Skeletochronology indicates that these specimens range in age from one to five years old. Analyzing bone tissue distribution and lines of arrested growth (LAGs) in these specimens, we estimate that Jeholosaurus reached sexual maturity at two to four years old. The largest individual (IVPP V15939) displays an apparently higher growth rate during the first two years, which is abruptly reduced in the following years, suggesting a distinct growth pattern that may be related to sexual dimorphism or variable environmental conditions. Finally, the largest specimen displays parallel-fibered bone tissue but lacks an external fundamental system (EFS) near the periphery, suggesting that it was still growing but was approaching somatic maturity at death.

摘要

骨组织学为恐龙的生活史提供了有价值的信息，生长线的存在为年龄估计，生长变异和古生物学重建提供了有用的信息。在这里，我们介绍了从早白垩纪热河生物群的非鬣蜥类鸟脚类恐龙热河蛇（Jeholosaurus shangyuanensis）的五个个体中获得的新数据。这些标本的体长从16到62 cm不等，分别代表了少年早期，少年晚期和亚成体发育阶段。剑龙的骨头主要由纤维状薄层组织组成，与其他非鬣蜥类鸟脚类动物相似；然而，在成年早期，通过亚成人个体也沉积了平行纤维骨和层状骨组织，这表明生长速度相对较慢。平行纤维骨仅在幼虫中局部存在，但在亚成体的最外层皮质中发育良好。骨骼年代学表明，这些标本的年龄范围从一岁到五岁。分析这些标本中的骨组织分布和停滞生长线（LAG），我们估计Jeholosaurus在两到四岁时达到性成熟。最大的个体（IVPP V15939）在头两年中表现出明显更高的增长率，在随后的几年中急剧下降，这表明可能存在与性二态性或可变的环境条件有关的独特增长模式。最后，最大的标本显示出平行纤维状的骨组织，但在外围附近没有外部基本系统（EFS），表明它仍在生长，但在死亡时已接近体细胞成熟。