Rollot Yann, Evers Serjoscha W, Joyce Walter G
Department of Geosciences, University of Fribourg, Fribourg, Switzerland.
PeerJ. 2021 Jan 21;8:e10475. doi: 10.7717/peerj.10475. eCollection 2021.
The cranial circulation and innervation systems of turtles have been studied for more than two centuries and extensively used to understand turtle systematics. Although a significant number of studies related to these structures exists, a broader comprehension of variation across the tree has been hindered by poor sampling and a lack of synthetic studies that addressed both systems together. We here provide new insights regarding the carotid circulation and facial nerve innervation systems in a broad set of extant turtles using CT (computed tomography) scans, which allow us to trace the canals these structures form in bone and understand the interaction between both systems. We document that the palatine artery, including the lateral carotid canal, is absent in all pleurodires and carettochelyids and was likely reduced or lost several times independently within Testudinoidea. We also highlight osteological correlates for the location of the mandibular artery. We finally summarize variation regarding the placement of the mandibular artery, location of the geniculate ganglion, placement of the hyomandibular and vidian nerves, and situations where we recommend caution when assessing canals in fossils. A morphometric study confirms that the relative sizes of the carotid canals are correlated with one another. Our results have the potential for building new phylogenetic characters and investigating the circulation systems of fossil taxa, which are expected to shed light on the evolution of the circulation system of turtles and clarify some unresolved relationships between fossil turtle clades.
龟类的颅循环和神经支配系统已经被研究了两个多世纪，并被广泛用于理解龟类的系统分类。尽管存在大量与这些结构相关的研究，但由于采样不足以及缺乏同时涉及这两个系统的综合研究，对整个龟类谱系中变异的更广泛理解受到了阻碍。我们在此利用CT（计算机断层扫描）扫描，对一系列现存龟类的颈动脉循环和面神经支配系统提供了新的见解，这使我们能够追踪这些结构在骨骼中形成的管道，并了解两个系统之间的相互作用。我们记录到，所有侧颈龟类和两爪鳖科动物都没有腭动脉，包括外侧颈动脉管，并且在曲颈龟亚目内可能多次独立地缩小或消失。我们还强调了下颌动脉位置的骨学相关特征。我们最后总结了关于下颌动脉位置、膝状神经节位置、舌颌神经和翼管神经位置的变异情况，以及在评估化石中的管道时我们建议谨慎对待的情况。一项形态测量研究证实，颈动脉管的相对大小相互关联。我们的研究结果有可能构建新的系统发育特征，并研究化石类群的循环系统，有望为龟类循环系统的进化提供线索，并澄清化石龟类分支之间一些尚未解决的关系。
