Evaluating the origin of Cynodontia (Synapsida, Therapsida) using 3D-Imaging Technologies

犬齿动物是最丰富和多样化的突触体类群，因为它包括哺乳动物，后者是在晚三叠世从非哺乳动物犬齿动物进化而来的。哺乳动物从犬齿动物进化而来，是化石记录中最被理解和研究最多的重大转变之一。相比之下，犬齿动物本身与其他突触体的起源却知之甚少。众所周知，犬齿动物与头类动物关系最为密切，但尚不清楚犬齿类和头类动物是否是姐妹类群，也不清楚头类动物与头类动物是否存在同源关系。此外，该支系最早成员的系统发育关系也存在不确定性。相比之下，较高的犬齿动物(真核牙齿)的关系被很好地理解。拟议项目的主要目标是根据新的CT数据重新评估真牙齿类(犬齿类+头类)的关系，并根据新的CT数据对该类群内的特征进化进行评估，即详细描述已知的最早的(晚二叠世和早三叠世)犬齿类和选定的类头类的内颅解剖。使用计算机断层扫描的现代3D成像技术可以使以前未见的内颅骨数据变得容易获得，这些数据在很大程度上是了解治疗进化的未开发资源，尽管它们比许多功能可变的外部颅骨特征更稳定和更有系统发育作用。使用这些数据检验的主要假设是，狗齿动物和头类动物是否是姐妹类群，还是犬齿动物是从头类动物内部进化而来的。此外，对内颅骨解剖的新见解有助于测试特征哺乳动物和狗科动物特征的起源是否可以追溯到真牙齿类系统发育的更深层次，同时允许研究微妙的内颅骨结构的深层次进化，如上翼状突起或泽泻类成分。最后，除了测试犬齿动物起源的问题外，新的数据还将有助于利用现代系统发育方法解决目前不稳定的早期犬齿动物和天牛头目动物之间的内部和相互关系。

Cynodontia is the most abundant and diverse group of synapsids, as it includes mammals, which evolved from non-mammalian cynodonts in the Late Triassic. The evolution of mammals from cynodonts is one of the best-understood and well-studied major transitions in the fossil record. In contrast, the origin of cynodonts themselves from other synapsids is very poorly known. It is well-established that cynodonts are most closely related to Therocephalia, but it is not clear whether cynodonts and therocephalians are sister-taxa or whether therocephalians are paraphyletic with regards to cynodonts. Also uncertainties exist concerning the phylogenetic relationships of the earliest member of this clade. By contrast, the relationships of higher cynodonts (eucynodonts) are well understood. The main objectives of the proposed project are a re-evaluation of the relationships of Eutheriodontia (Cynodontia+Therocephalia) and an assessment of character evolution within the group based on new CT data, i.e. detailed descriptions of the endocranial anatomy of the earliest known (late Permian and Early Triassic) cynodonts and selected therocephalian relatives. Modern 3D-imaging technologies using computed tomography can make previously-unseen endocranial data readily available, which are a largely untapped resource for understanding therapsid evolution, despite their greater stability and phylogenetic utility than many functionally-variable external craniodental characters. The primary hypothesis to be tested using these data is whether Cynodontia and Therocephalia are sister-taxa or whether cynodonts evolved from within Therocephalia. Furthermore, the novel insights into the endocranial anatomy are useful to test if the origin of characteristic mammalian but also cynodont characters can be traced back deeper in eutheriodont phylogeny and allow, at the same time, to investigate the deep-time evolution of delicate endocranial structures, such as the epipterygoid or alisphenoid elements. Finally, in addition to testing questions of cynodont origins, the new data will also help to resolve the currently unstable intra- and interrelationships among early cynodonts and therocephalians using modern phylogenetic approaches.