Conflicting evidence for the use of caudal autotomy in mesosaurs
Conflicting evidence for the use of caudal autotomy in mesosaurs
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DOI：
10.1038/s41598-020-63625-0
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发表时间：
2020-04-28
影响因子：
4.6
通讯作者：
Froebisch, Joerg
中科院分区：
文献类型：
--
作者：
MacDougall, Mark J.;Verriere, Antoine;Froebisch, Joerg
早二叠世的中龙是第一个重新入侵水生环境的恐龙。它们最有争议和最令人困惑的特征之一是它们独特的尾部解剖结构，这被认为是促进尾部自切的机制。一些研究人员描述了中龙尾椎的假定断裂面--尾椎中央的未骨化区域--在许多现存的有鳞动物中，这些断裂面允许尾巴分离，使动物逃脱捕食。然而，除了初步描述之外，关于中龙类断裂面的报道从未被仔细研究过，这引起了怀疑。在这里，使用大量的脊椎系列，组织学和X射线计算机断层扫描，我们提供了一个详细的说明骨折平面在所有三个物种的中龙。鉴于尾巴在许多其他水生爬行动物中对推进的重要性，确定中龙的断裂面对它们的水生运动具有重要意义。尽管中龙显然有能力自断尾巴，但由于缺乏捕食压力，而且在有关节的标本中没有自断尾巴的记录，它们实际上不太可能利用这种行为。我们认为，断裂面在中龙的存在是一个进化的遗迹，并可能代表一个尚未确定的陆生分支的古生代古龙类，包括最早的辐射次生水生四足动物的突触。
The early Permian mesosaurs were the first amniotes to re-invade aquatic environments. One of their most controversial and puzzling features is their distinctive caudal anatomy, which has been suggested as a mechanism to facilitate caudal autotomy. Several researchers have described putative fracture planes in mesosaur caudal vertebrae - unossified regions in the middle of caudal vertebral centra - that in many extant squamates allow the tail to separate and the animal to escape predation. However, the reports of fracture planes in mesosaurs have never been closely investigated beyond preliminary descriptions, which has prompted scepticism. Here, using numerous vertebral series, histology, and X-ray computed tomography, we provide a detailed account of fracture planes in all three species of mesosaurs. Given the importance of the tail for propulsion in many other aquatic reptiles, the identification of fracture planes in mesosaurs has important implications for their aquatic locomotion. Despite mesosaurs apparently having the ability to autotomize their tail, it is unlikely that they actually made use of this behaviour due to a lack of predation pressure and no record of autotomized tails in articulated specimens. We suggest that the presence of fracture planes in mesosaurs is an evolutionary relic and could represent a synapomorphy for an as-yet undetermined terrestrial clade of Palaeozoic amniotes that includes the earliest radiation of secondarily aquatic tetrapods.