Long bone histology of sauropterygia from the lower Muschelkalk of the Germanic basin provides unexpected implications for phylogeny.
Long bone histology of sauropterygia from the lower Muschelkalk of the Germanic basin provides unexpected implications for phylogeny.
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DOI：
10.1371/journal.pone.0011613
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发表时间：
2010-07-21
期刊：
影响因子：
3.7
通讯作者：
Klein N
中科院分区：
文献类型：
--
作者：
Klein N
蜥脚类是三叠纪海洋爬行动物中数量丰富而成功的一个类群。三叠纪龙翼类的系统发育关系一直不稳定，最近受到质疑。虽然标本数量很多，但主要的问题是日耳曼盆地的诊断材料稀少，以及始龙蜥类的颅后形态一致。在目前的文件中，肱骨沿着与其相应的骨组织学下到中Muschelkalk sauropakians的形态描述和解释首次在系统发育的背景下。 假龙显示出典型的类形层状带状骨骼类型，但不同的生长模式和一个新的肱骨形态类型的出现表明其分类多样性比已知的要高。相比之下，巨大的形态变化eosauropterygian肱骨不分配给假龙，他们的长骨组织学是相对统一的，可以分为两个组织型。出乎意料的是，这两种组织型都显示了整个皮质中丰富的纤维板层骨。这就将龙类中纤维板层骨的起源从白垩纪推回到了中三叠世早期（早安尼世）。组织型A被分配到管龙属，它是盾龙总科的基底成员，其中包括蛇颈龙作为衍生成员。组织型B与厚肋龙属的Anarosaurus有关。与这些新发现相反，在地层上较年轻的厚肋龙属新狮龙显示出类形的层状带状骨型和不完全的软骨内骨化，就像假龙一样。组织学的结果假设讨论了在一个遗传学的背景下有很大的影响，目前的系统发育假说的Sauropterygia，离开pachypleurosaurs多系。根据组织学数据，新角龙可能与幻龙有亲缘关系，而阿纳龙则属于盾龙的分支。此外，纤维板层骨的存在，伴随着增长率的增加，甚至可能伴随着代谢率的增加，已经存在于阿纳龙和管龙中，可以解释盾龙总科的成功，唯一幸存到侏罗纪的龙翼类，并产生了远洋蛇颈龙辐射。
Sauropterygia is an abundant and successful group of Triassic marine reptiles. Phylogenetic relationships of Triassic Sauropterygia have always been unstable and recently questioned. Although specimens occur in high numbers, the main problems are rareness of diagnostic material from the Germanic Basin and uniformity of postcranial morphology of eosauropterygians. In the current paper, morphotypes of humeri along with their corresponding bone histologies for Lower to Middle Muschelkalk sauropterygians are described and interpreted for the first time in a phylogenetic context. Nothosaurus shows a typical plesiomorphic lamellar-zonal bone type, but varying growth patterns and the occurrence of a new humerus morphotype point to a higher taxonomic diversity than was known. In contrast to the enormous morphological variability of eosauropterygian humeri not assigned to Nothosaurus, their long bone histology is relatively uniform and can be divided into two histotypes. Unexpectedly, both of these histotypes reveal abundant fibrolamellar bone throughout the cortex. This pushes the origin of fibrolamellar bone in Sauropterygia back from the Cretaceous to the early Middle Triassic (early Anisian). Histotype A is assigned to Cymatosaurus, a basal member of the Pistosauroidea, which includes the plesiosaurs as derived members. Histotype B is related to the pachypleurosaur Anarosaurus. Contrary to these new finds, the stratigraphically younger pachypleurosaur Neusticosaurus shows the plesiomorphic lamellar-zonal bone type and an incomplete endochondral ossification, like Nothosaurus. Histological results hypothetically discussed in a phylogenetical context have a large impact on the current phylogenetic hypothesis of Sauropterygia, leaving the pachypleurosaurs polyphyletic. On the basis of histological data, Neusticosaurus would be related to Nothosaurus, whereas Anarosaurus would follow the pistosaur clade. Furthermore, the presence of fibrolamellar bone, which is accompanied with increased growth rates and presumably even with increased metabolic rates, already in Anarosaurus and Cymatosaurus can explain the success of the Pistosauroidea, the only sauropterygian group to survive into the Jurassic and give rise to the pelagic plesiosaur radiation.
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