Oklahoma State University Center for Health Sciences, Tulsa, Oklahoma, United States of America.
Museums Victoria, Melbourne, Victoria, Australia.
Sci Rep. 2018 Jan 18;8(1):1162. doi: 10.1038/s41598-018-19362-6.
High-latitude (i.e., "polar") Mesozoic fauna endured months of twilight and relatively low mean annual temperatures. Yet non-avian dinosaurs flourished in this taxing environment. Fossils of basal ornithopod dinosaurs ("hypsilophodontids") are common in the Early Cretaceous high-latitude sediments of Victoria, Australia, and four taxa have been described; although their ontogenetic histories are largely unexplored. In the present study, eighteen tibiae and femora were utilized in the first multi-specimen ontogenetic histological analysis of Australian polar hypsilophodontids. The sample consists of eleven individuals from the Flat Rocks locality (Late Valanginian or Barremian), and five from the Dinosaur Cove locality (Albian). In both groups, growth was most rapid during the first three years, and skeletal maturity occurred between five and seven years. There is a weak asymptotic trend in a plot of growth mark count versus femur length, with considerable individual variation. Histology suggests two genera are present within the Dinosaur Cove sample, but bone microstructure alone could not distinguish genera within the Flat Rocks sample, or across the two geologically separate (~ 26 Ma) localities. Additional histologic sampling, combined with morphological analyses, may facilitate further differentiation between ontogenetic, individual, and species variation.
高纬度（即“极地”）中生代动物经历了数月的黄昏和相对较低的年平均温度。然而，非鸟类恐龙在这种苛刻的环境中蓬勃发展。基础鸟脚亚目恐龙（“虚骨龙类”）的化石在澳大利亚维多利亚州的早白垩世高纬度沉积物中很常见，已经描述了四个分类群；尽管它们的个体发育历史在很大程度上尚未得到探索。在本研究中，18 个胫骨和股骨被用于对澳大利亚极地虚骨龙类的第一个多标本个体发育组织学分析。该样本由来自 Flat Rocks 地点（晚巴雷姆阶或早白垩世）的 11 个个体和来自 Dinosaur Cove 地点（阿尔比阶）的 5 个个体组成。在这两个群体中，生长速度在头三年最快，骨骼成熟发生在五到七年之间。在生长标记计数与股骨长度的关系图上存在微弱的渐近趋势，个体间存在较大差异。组织学表明，在 Dinosaur Cove 样本中存在两个属，但仅凭骨微观结构无法区分 Flat Rocks 样本中的属，也无法区分两个在地质上分离的（~26Ma）地点。进一步的组织学采样，结合形态分析，可能有助于进一步区分个体发育、个体和物种变异。
