Anatomy, Ecology and Ontogeny of Mesosaurs using 3D-Imaging Technologies

中龙是一个独特的和非常专业的脊椎动物群体，代表了第一个完全水栖的恐龙。中龙科通常被认为属于副爬行纲，尽管一些研究表明它们代表了副爬行纲和真爬行纲之外的基底蜥脚类。它们仅在冈瓦纳南部的早二叠世被发现。然而，尽管它们的地层和地理范围有限，但它们代表了四足动物进化史上的重要一步：具有非常长的鼻子，长而细的锥形牙齿，细长的脖子，长而扁平的尾巴，以及桨状的前肢和后肢，高度专门化为水生生活方式。目前只有三个单型的中龙科属被确认为有效的：细齿中龙（Mesosaurus tenuidens）、圆胸硬龙（Stereosternum tumarium）和巴西龙（Brazilosaurus sanpauloensis）。虽然它们在恐龙早期的进化史上是一个重要的类群，但对中龙科的了解却很少，尽管最近对中龙科的研究取得了一些进展。纤弱的拟议项目的主要目标包括使用现代3D成像技术从CT数据中对剩余的中龙类Stereosternum和Brazilosaurus进行详细的解剖学调查，以揭示新的系统发育特征，以测试现有的关于它们之间和内部关系的假设。计划中的3D重建的一般中龙类头骨解剖的目的是解决有争议的和历史的问题，无论是中龙类的头骨条件是anapsid或synapsid。拟议的头骨3D分析（包括其内部颅骨结构，如脑壳，颅骨内模和内耳）旨在进一步填补我们知识的空白，并产生重要数据来了解早期进化的头骨。此外，有限元分析（FEA）将被应用于头骨的Stereosternum和巴西龙和其他现存的和化石次生水生四足动物相比，以测试各自的咬合力和头骨阻力，并测试是否有不同的进食行为（滤食动物与主动捕食者）和运动之间的中龙科类群。最后，一个彻底的个体发育研究，特别关注整体postcranial（但也颅）的比例，应用形态测量方法，包括线性测量以及几何形态测量的目的是调查潜在的变化中的生长模式的mesosauids，因此是否有一个差异，在少年和成年mesosauids之间的喂养行为。这项研究的结果有望对这些最早的次生水生生物的古生物学有新的见解。

Mesosaurs are a unique and very specialized vertebrate group, representing the first fully aquatic amniotes. Mesosaurids are commonly considered to belong to Parareptilia, although some studies suggest that they represent basal sauropsids outside of the split between parareptiles and eureptiles. They are exclusively known from the early Permian of southern Gondwana. However, despite their restricted stratigraphic and geographic range, they represent an important step in the evolutionary history of tetrapods: being highly specialized for an aquatic lifestyle by having a long skull with an extremely elongate snout, spiked with long and thin conical teeth, a slender neck, a long flattened tail for laterally undulating movements, and paddle-like fore and hind limbs. Only three monotypic mesosaurid genera are currently recognized as valid: Mesosaurus tenuidens, Stereosternum tumidum, and Brazilosaurus sanpauloensis. Although they represent a key group in the early evolutionary history of amniotes, mesosaurids are quite poorly known, despite some recent research advances on M. tenuidens. The main objectives of the proposed project comprise a detailed anatomical investigation of the remaining mesosaurids Stereosternum and Brazilosaurus using modern 3D imaging technologies from CT data to reveal new phylogenetic characters to test existing hypotheses about their inter- and intrarelationships. The planned 3D reconstruction of the general mesosaurid skull anatomy aims to resolve the controversial and historical question of whether the skull condition of mesosaurids is anapsid or synapsid. The proposed 3D analysis of the skull (including its internal cranial structures such as the braincase, cranial endocast and inner ear) aims to further fill a gap in our knowledge, and yield important data to understand the early evolution of the amniote skull. Moreover, a Finite Element Analysis (FEA) will be applied to skulls of Stereosternum and Brazilosaurus and compared to other extant and fossil secondarily aquatic tetrapods to test their respective bite power and skull resistance and to test whether there are differences in feeding behaviour (filter-feeders vs. active predators) and locomotion among the mesosaurid taxa. Finally, a thorough ontogenetic study with special focus on overall postcranial (but also cranial) proportions, applying a morphometric approach including linear measurements as well as geometric morphometrics aims to investigate potential variations in the growth patterns of mesosaurids, and hence whether there was a difference in feeding behaviour between juvenile and adult mesosaurids. The results of this research promise novel insights into the palaeobiology of these earliest secondarily aquatic amniotes.