External and internal structure of ankylosaur (Dinosauria, Ornithischia) osteoderms and their systematic relevance

ABSTRACTAnkylosaurian systematics can be assessed using morphological, textural, and histological characters of osteoderms. Archosaur osteoderms have cortices surrounding cancellous cores. Ankylosaurs are united by an external cortex distinguishable from the core and by the presence of mineralized structural fibers. Nodosaurid osteoderms lack a well-developed basal cortex and have dense external cortical fibers. Ankylosaurid osteoderms are thinner than those of other ankylosaurs. Polacanthine osteoderms have a cancellous core, but share this feature with other derived and primitive taxa. Cortical thickness overlaps among groups, so a thick cortex is not diagnostic for polacanthines. Specialized elements diverge histologically from the primitive condition to suit their specific functions. Some shapes and external textures are diagnostic for specific taxa, such as <i>Ankylosaurus</i> and <i>Glyptodontopelta</i>. Parsimony analyses suggest osteodermal support for a monophyletic Polacanthinae (excluding <i>Mymoorapelta</i>) and Shamosaurinae.SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP

ABSTRACT：可通过骨板（osteoderms）的形态学、纹理学及组织学特征评估甲龙类（Ankylosaurian）的分类系统学。主龙类（Archosaur）的骨板具有包裹松质骨核心的皮质层。甲龙类以两项特征作为共同鉴定依据：一是存在区别于核心的外皮质层，二是具备矿化结构纤维。结节龙科（Nodosauridae）的骨板缺乏发育完善的基皮质层，且外皮质纤维较为致密。甲龙科（Ankylosauridae）的骨板厚度小于其他甲龙类类群。多刺甲龙亚科（Polacanthinae）的骨板具有松质骨核心，但该特征同样存在于其他衍生与原始类群中。不同类群的皮质厚度存在重叠现象，因此厚皮质层并非多刺甲龙亚科的专属鉴定特征。特化骨板在组织学层面偏离原始状态，以适配其特定功能。部分骨板的形状与外部纹理可作为特定类群的鉴定依据，例如甲龙属（Ankylosaurus）与雕齿甲龙属（Glyptodontopelta）。简约性分析（Parsimony analysis）结果显示，骨板特征支持单系群（monophyletic）多刺甲龙亚科（排除迈摩尔甲龙属Mymoorapelta）与沙摩龙亚科（Shamosaurinae）的单系有效性。
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