Stefanic Candice M, Nesbitt Sterling J
Department of Geosciences, Virginia Polytechnic Institute and State University (Virginia Tech), Blacksburg, VA, USA.
PeerJ. 2018 Feb 14;6:e4235. doi: 10.7717/peerj.4235. eCollection 2018.
Dinosaurs and their close relatives grew to sizes larger than any other terrestrial animal in the history of life on Earth, and many enormous dinosaurs (e.g., , , ) have accessory intervertebral articulations that have been suggested to support these large body sizes. Some pseudosuchian archosaurs have been reported to have these articulations as well, but few have been characterized in these taxa because of a lower abundance of complete, three-dimensional pseudosuchian vertebral material in relation to dinosaurs. We describe the axial column of the large (∼4-5 m) poposauroid pseudosuchian from the Upper Triassic of Texas (TMM Locality 31025 of the Otis Chalk localities; Dockum Group, Howard County, TX, USA). was originally named from pelvic girdle elements and vertebrae; here we describe newly discovered and prepared presacral vertebrae and a presacral rib from the original excavation of the holotype in the 1940s. The well-preserved vertebrae have well-defined vertebral laminae and clear hyposphene-hypantrum intervertebral articulations, character states mentioned in pseudosuchians but rarely described. The new material demonstrates variation present in the hyposphene-hypantrum articulation through the vertebral column. We compared these morphologies to other pseudosuchians with and without the hyposphene-hypantrum articulation. Based on these careful comparisons, we provide an explicit definition for the hyposphene-hypantrum articulation applicable across Archosauria. Within Pseudosuchia, we find the hyposphene-hypantrum appeared independently in the clade at least twice, but we also see the loss of these structures in clades that had them ancestrally. Furthermore, we found the presence of large body sizes (femoral lengths >∼300 mm) and the presence of the hyposphene-hypantrum is correlated in most non-crocodylomorph pseudosuchian archosaurs with a few exceptions. This result suggests that the presence of the hyposphene-hypantrum is controlled by the increases and decreases in body size and not strictly inheritance.
恐龙及其近亲长得比地球生命史上的任何其他陆地动物都要大，许多巨型恐龙（如 、 、 ）都有辅助椎间关节，有人认为这些关节支撑了它们庞大的体型。据报道，一些伪鳄类主龙也有这些关节，但由于与恐龙相比，完整的三维伪鳄类脊椎材料较少，因此在这些类群中对其进行描述的很少。我们描述了来自美国得克萨斯州上三叠统的大型（约4 - 5米）波波龙类伪鳄类 的脊柱。 最初是根据骨盆带元素和椎骨命名的；在这里，我们描述了20世纪40年代从正模标本的原始挖掘中发现并准备好的荐前椎骨和一根荐前肋骨。保存完好的椎骨有清晰的椎板和明显的下椎弓突 - 椎下凹椎间关节，这些特征在伪鳄类中曾有提及，但很少被描述。新材料展示了整个脊柱中下椎弓突 - 椎下凹关节的变化。我们将这些形态与有和没有下椎弓突 - 椎下凹关节的其他伪鳄类进行了比较。基于这些仔细的比较，我们为适用于整个主龙类的下椎弓突 - 椎下凹关节提供了一个明确的定义。在伪鳄类中，我们发现下椎弓突 - 椎下凹至少在该分支中独立出现了两次，但我们也看到在祖先具有这些结构的分支中这些结构消失了。此外，我们发现大多数非鳄形类伪鳄类主龙中，大体型（股骨长度>约300毫米）的存在与下椎弓突 - 椎下凹的存在相关，但有少数例外。这一结果表明，下椎弓突 - 椎下凹的存在受体型大小增减的控制，而非严格受遗传控制。
