Postcrania of juvenile Pinacosaurus grangeri (Ornithischia: Ankylosauria) from the Upper Cretaceous Alagteeg Formation, Alag Teeg, Mongolia: implications for ontogenetic allometry in ankylosaurs

The ankylosaurine Pinacosaurus is one of the best known ankylosaur to date in terms of the number and preservational quality of specimens. Juvenile to sub-adult postcrania collected by the Soviet-Mongolian Paleontological Expedition from the Upper Cretaceous Alagteeg Formation at Alag Teeg, Mongolia can be assigned to Pinacosaurus grangeri based on discrete cranial characters. One individual is significantly larger than the others and demonstrates delayed fusion of postcranial elements with the earliest occurring between dorsal ribs and vertebrae. The robustness of forelimb elements is positively allometric with respect to their length, indicating weight-bearing relationship. Such length-dependent correlations are not seen in the hind limbs. Finally, incipient cervical half rings suggest a developmental pathway of outgrowths from the underlying band combined with fusion of overlying osteoderms.

甲龙亚科的绘龙（Pinacosaurus）是目前已知标本数量最多、保存质量最佳的甲龙类群之一。由苏蒙古生物考察队于蒙古国阿拉特格的上白垩统阿拉特格组采集的幼年至亚成年个体颅后骨骼，可通过独立头骨鉴别特征归为格氏绘龙（Pinacosaurus grangeri）。其中一件个体的体型显著大于其余标本，其颅后骨骼的骨愈合进程存在延迟现象，最早的愈合事件发生于背肋与椎骨之间。前肢骨骼的粗壮程度与其长度呈正异速生长关系，表明前肢具备承重功能；而后肢骨骼中并未观察到此类与长度相关的生长相关性。此外，该类群已出现初期发育的颈盾半环，提示其发育路径为：从下方的颈带向外长出突起，并与上方覆盖的骨板相互融合。