Holwerda Femke M, Evans Mark, Liston Jeff J
Staatliche Naturwissenschaftliche Sammlungen Bayerns (SNSB), Bayerische Staatssamlung für Paläontologie und Geologie, Munich, Germany.
Faculty of Geosciences, Utrecht University, Utrecht, Netherlands.
PeerJ. 2019 Feb 14;7:e6404. doi: 10.7717/peerj.6404. eCollection 2019.
Four isolated sauropod axial elements from the Oxford Clay Formation (Callovian, Middle Jurassic) of Peterborough, UK, are described. Two associated posterior dorsal vertebrae show a dorsoventrally elongated centrum and short neural arch, and nutrient or pneumatic foramina, most likely belonging to a non-neosauropod eusauropod, but showing ambiguous non-neosauropod eusauropod and neosauropod affinities. An isolated anterior caudal vertebra displays a ventral keel, a 'shoulder' indicating a wing-like transverse process, along with a possible prespinal lamina. This, together with an overall high complexity of the anterior caudal transverse process (ACTP) complex, indicates that this caudal could have belonged to a neosauropod. A second isolated middle-posterior caudal vertebra also shows some diagnostic features, despite the neural spine and neural arch not being preserved and the neurocentral sutures being unfused. The positioning of the neurocentral sutures on the anterior one third of the centrum indicates a middle caudal position, and the presence of faint ventrolateral crests, as well as a rhomboid anterior articulation surface, suggest neosauropod affinities. The presence of possible nutrient foramina are only tentative evidence of a neosauropod origin, as they are also found in Late Jurassic non-neosauropod eusauropods. As the caudals from the two other known sauropods from the Peterborough Oxford Clay, and an indeterminate non-neosauropod eusauropod, do not show the features seen on either of the new elements described, both isolated caudals indicate a higher sauropod species diversity in the faunal assemblage than previously recognised. An exploratory phylogenetic analysis using characters from all four isolated elements supports a basal neosauropod placement for the anterior caudal, and a diplodocid origin for the middle caudal. The dorsal vertebrae are an unstable OTU, and therefore remain part of an indeterminate eusauropod of uncertain affinities. Together with , and other material assigned to different sauropod groups, this study indicates the presence of a higher sauropod biodiversity in the Oxford Clay Formation than previously recognised. This study shows that it is still beneficial to examine isolated elements, as these may be indicators for higher species richness in deposits that are otherwise poor in terrestrial fauna.
本文描述了来自英国彼得伯勒牛津黏土地层（卡洛夫阶，中侏罗世）的四块孤立的蜥脚类恐龙轴向骨骼化石。两块相连的后背部脊椎骨显示出椎体背腹向拉长且神经弓较短，还有营养孔或气腔孔，极有可能属于非新蜥脚类真蜥脚类恐龙，但显示出与非新蜥脚类真蜥脚类恐龙及新蜥脚类恐龙的亲缘关系并不明确。一块孤立的前尾椎有腹侧龙骨、一个表明有翼状横突的“肩部”，还有一个可能的椎前板。这一点，再加上前尾椎横突（ACTP）复合体总体上的高度复杂性，表明这块尾椎可能属于新蜥脚类恐龙。另一块孤立的中后尾椎尽管神经棘和神经弓未保存且神经中央缝未愈合，但也显示出一些鉴别特征。神经中央缝在椎体前三分之一处的位置表明其为中尾椎位置，微弱的腹外侧嵴以及菱形的前关节面的存在表明其与新蜥脚类恐龙有亲缘关系。可能存在的营养孔只是新蜥脚类恐龙起源的初步证据，因为在晚侏罗世的非新蜥脚类真蜥脚类恐龙中也能发现。由于来自彼得伯勒牛津黏土的另外两种已知蜥脚类恐龙的尾椎，以及一种未确定的非新蜥脚类真蜥脚类恐龙的尾椎，并未显示出上述新描述的任何一块骨骼化石的特征，这两块孤立的尾椎表明该动物群组合中的蜥脚类恐龙物种多样性比之前认为的更高。利用所有四块孤立骨骼化石的特征进行的探索性系统发育分析支持将前尾椎置于基础新蜥脚类恐龙的位置，将中尾椎置于梁龙科起源的位置。这些背椎是一个不稳定的操作分类单元，因此仍属于亲缘关系不确定的未确定真蜥脚类恐龙的一部分。与 以及其他归入不同蜥脚类恐龙类群的材料一起，这项研究表明牛津黏土地层中蜥脚类恐龙的生物多样性比之前认为的更高。这项研究表明，对孤立的骨骼化石进行研究仍然是有益的，因为这些化石可能是陆地动物群稀少的沉积物中物种丰富度更高的指示物。
