Northeastern Research Institute of Petrified Wood and Mineral Resources, Nakhon Ratchasima Rajabhat University, Suranaree Subdistict, Mueang, Nakhon Ratchasima District, Nakhon Ratchasima, Thailand.
Institute of Dinosaur Research, Fukui Prefectural University, Kenjojima, Matsuoka, Eiheiji-Cho, Fukui, Japan.
PLoS One. 2019 Oct 9;14(10):e0222489. doi: 10.1371/journal.pone.0222489. eCollection 2019.
The isolated fossil remains of an allosauroid theropod from the Lower Cretaceous Khok Kruat Formation of Khorat, Thailand, are described in this study. Detailed observations support the establishment of a new allosauroid, Siamraptor suwati gen. et sp. nov. This new taxon is based on a composite cranial and postcranial skeleton comprising premaxilla, maxilla, jugal, surangular, prearticular, articular, vertebrae, manual ungual, ischium, tibia, and pedal phalanx. It is distinguished from other allosauroids by characters such as a jugal with straight ventral margin and dorsoventrally deep anterior process below the orbit, a surangular with a deep oval concavity at the posterior end of the lateral shelf and four posterior surangular foramina, a long and narrow groove along the suture between the surangular and the prearticular, an articular with a foramen at the notch of the suture with the prearticular, an anterior cervical vertebra with a pneumatic foramen (so-called 'pleurocoel') excavating parapophysis, and cervical and posterior dorsal vertebrae penetrated by a pair of small foramina bilaterally at the base of the neural spine. The presence of a huge number of camerae and pneumatopores in cranial and axial elements reveals a remarkable skeletal pneumatic system in this new taxon. Moreover, the phylogenetic analyses revealed that Siamraptor is a basal taxon of Carcharodontosauria, involving a new sight of the paleobiogeographical context of this group. Siamraptor is the best preserved carcharodontosaurian theropod in Southeast Asia, and it sheds new light on the early evolutionary history of Carcharodontosauria.
本研究描述了来自泰国呵叻府下白垩统科克克鲁阿特组的一种鲨齿龙超科兽脚类恐龙的孤立化石遗骸。详细的观察结果支持建立一个新的鲨齿龙超科恐龙，暹罗龙属 suwati 种。这个新的分类单元是基于一个复合的头骨和后躯骨骼组成，包括前颌骨、上颌骨、颧骨、方颧骨、前关节、关节、脊椎、手爪、坐骨、胫骨和跖骨。它与其他鲨齿龙超科恐龙的区别在于其特征，如颧骨的腹缘笔直，眶下前缘的前突在垂直和水平方向上都很深，方颧骨的外侧板后端有一个深的椭圆形凹陷和四个后方颧骨孔，方颧骨和前关节之间的缝合线上有一个长而窄的沟，关节与前关节的缝合线上有一个孔，前颈椎有一个在椎突上的气腔（所谓的“肋腔”），以及颈椎和后背椎的神经棘基部有一对小的双侧孔。头骨和轴骨元素中大量的气腔和气囊揭示了这个新分类单元具有显著的骨骼充气系统。此外，系统发育分析表明，暹罗龙是鲨齿龙科的基干类群，涉及到该类群古生物地理背景的新视角。暹罗龙是东南亚保存最完好的鲨齿龙类兽脚类恐龙，它为鲨齿龙类的早期进化历史提供了新的认识。
