Museum of Paleontology and Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan, United States of America.
PLoS One. 2011 Feb 28;6(2):e17114. doi: 10.1371/journal.pone.0017114.
The axial skeleton of extinct saurischian dinosaurs (i.e., theropods, sauropodomorphs), like living birds, was pneumatized by epithelial outpocketings of the respiratory system. Pneumatic signatures in the vertebral column of fossil saurischians include complex branching chambers within the bone (internal pneumaticity) and large chambers visible externally that are bounded by neural arch laminae (external pneumaticity). Although general aspects of internal pneumaticity are synapomorphic for saurischian subgroups, the individual internal pneumatic spaces cannot be homologized across species or even along the vertebral column, due to their variability and absence of topographical landmarks. External pneumatic structures, in contrast, are defined by ready topological landmarks (vertebral laminae), but no consistent nomenclatural system exists. This deficiency has fostered confusion and limited their use as character data in phylogenetic analysis.
METHODOLOGY/PRINCIPAL FINDINGS: We present a simple system for naming external neural arch fossae that parallels the one developed for the vertebral laminae that bound them. The nomenclatural system identifies fossae by pointing to reference landmarks (e.g., neural spine, centrum, costal articulations, zygapophyses). We standardize the naming process by creating tripartite names from "primary landmarks," which form the zygodiapophyseal table, "secondary landmarks," which orient with respect to that table, and "tertiary landmarks," which further delineate a given fossa.
CONCLUSIONS/SIGNIFICANCE: The proposed nomenclatural system for lamina-bounded fossae adds clarity to descriptions of complex vertebrae and allows these structures to be sourced as character data for phylogenetic analyses. These anatomical terms denote potentially homologous pneumatic structures within Saurischia, but they could be applied to any vertebrate with vertebral laminae that enclose spaces, regardless of their developmental origin or phylogenetic distribution.
已灭绝的蜥脚形亚目恐龙（即兽脚亚目、蜥脚形亚目恐龙）的轴骨骼与现生鸟类一样，是由呼吸系统的上皮外突形成的。化石蜥脚形亚目恐龙脊柱中的气腔特征包括骨骼内的复杂分支腔室（内部充气）和外部可见的由神经弓薄板包围的大腔室（外部充气）。尽管内部充气的一般特征是蜥脚形亚目各分组的共有特征，但由于其可变性和缺乏地形标志，单个内部充气空间无法在物种间甚至沿脊柱进行同源化。相比之下，外部充气结构则由现成的地形标志（椎弓薄板）定义，但不存在一致的命名系统。这种缺陷导致了混淆，并限制了它们作为系统发育分析中特征数据的使用。
方法/主要发现：我们提出了一种简单的命名外部神经弓凹窝的系统，该系统与界定它们的椎弓薄板系统相似。该命名系统通过指向参考标志（例如，神经棘、椎体、肋关节、关节突）来识别凹窝。我们通过从形成关节突关节面的“主要标志”、相对于该面定向的“次要标志”和进一步划定特定凹窝的“三级标志”创建三分体名称来标准化命名过程。
结论/意义：建议的椎弓薄板界定凹窝命名系统增加了对复杂椎体描述的清晰度，并允许将这些结构作为系统发育分析的特征数据来源。这些解剖学术语表示在蜥脚形亚目中可能具有同源性的充气结构，但它们可以应用于任何具有封闭空间的脊椎动物，而不论其发育起源或系统发育分布如何。
