Virtual reexamination of a plesiosaurian specimen (Reptilia, Plesiosauria) from the Late Cretaceous (Turonian) of Goulmima, Morocco, using computed tomography

Turonian deposits of the Goulmima area, Er-Rachidia Province in southern Morocco, have yielded a diverse marine vertebrate fauna, including chondrichthyans, bony fishes, and large marine reptiles such as plesiosaurians, mosasauroids, and turtles. These fossils are included in ovoid calcareous nodules that are difficult to prepare. Moreover, bones may be partially or totally dissolved, making their study difficult. Using computed tomography, we have reconstructed the entire skull anatomy of SMNS 81783, one of the rare plesiosaurian specimens found in this locality and more generally in Africa. The digital three-dimensional reconstruction of the skull and the mandible offers for the first time the possibility to describe this specimen exhaustively. The new anatomical characters recorded confirm that SMNS 81783 belongs to Elasmosauridae on the basis of (1) slender and triangular skull; (2) beak index equal to 42%; (3) temporal fossa estimated to occupy about 40% of the skull length; (4) long process of the premaxillae extending posteriorly to meet the parietal above the orbit and separating the frontals; and (5) margin of the temporal fenestra lacking obvious contribution from the frontal. A preliminary phylogenetic analysis confirms its elasmosaurid affinity. The relationships between SMNS 81783, <i>Libonectes atlasense</i>, and <i>Libonectes morgani</i>, as well as the presence of stapes and pineal foramen, are discussed. SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP Citation for this article: Allemand, R., N. Bardet, A. Houssaye, and P. Vincent. 2017. Virtual reexamination of a plesiosaurian specimen (Reptilia, Plesiosauria) from the Late Cretaceous (Turonian) of Goulmima, Morocco, using computed tomography. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2017.1325894.

摩洛哥南部埃尔拉希迪亚省古利米马地区的土仑阶（Turonian）地层产出了多样的海洋脊椎动物群，包括软骨鱼类、硬骨鱼类以及蛇颈龙类（plesiosaurians）、沧龙类（mosasauroids）和龟类等大型海生爬行动物。这些化石保存在难以制备的卵圆形钙质结核中。此外，骨骼可能发生部分或完全溶解，进一步增加了研究难度。本研究利用计算机断层扫描（computed tomography，CT）技术，对SMNS 81783的完整头骨解剖结构进行了重建——该标本是该地区乃至全非洲罕见的蛇颈龙类化石之一。此次对头骨与下颌骨的数字化三维重建，首次为该标本的全面描述提供了可能。本次记录的全新解剖学特征证实，SMNS 81783隶属于薄板龙科（Elasmosauridae），依据如下：1）头骨纤细呈三角形；2）喙部指数为42%；3）颞窝长度约占头骨总长的40%；4）前上颌骨的长突向后延伸，在眼眶上方与顶骨相接并分隔额骨；5）颞颥孔边缘未明显包含额骨成分。初步的系统发育分析进一步验证了其薄板龙科的分类归属。本文还讨论了SMNS 81783与阿特拉斯游龙（Libonectes atlasense）、摩根游龙（Libonectes morgani）之间的系统发育关系，以及镫骨（stapes）和松果孔（pineal foramen）的存在情况。补充数据——本文的补充材料可通过www.tandfonline.com/UJVP免费获取。本文引用格式：Allemand R., Bardet N., Houssaye A., Vincent P., 2017. 基于计算机断层扫描的摩洛哥古利米马晚白垩世（土仑阶）蛇颈龙类标本（爬行纲：蛇颈龙目）的虚拟再研究. 脊椎动物古生物学杂志. DOI: 10.1080/02724634.2017.1325894.