A reexamination of Milosaurus mccordi, and the evolution of large body size in Carboniferous synapsids
A reexamination of Milosaurus mccordi, and the evolution of large body size in Carboniferous synapsids
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DOI：
10.1080/02724634.2018.1508026
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发表时间：
2018-09-03
影响因子：
1.4
通讯作者：
Froebisch, Joerg
中科院分区：
文献类型：
--
作者：
Brocklehurst, Neil;Froebisch, Joerg
Milosaurus mccordi在1970年被描述为一种来自伊利诺伊州石炭纪晚期的大型，pelycosaurian级突触，但此后很少受到关注。在这里，正模和参考材料的Milosaurus重新审查，并纳入系统发育分析。Milosaurus被分解在Haptodontiformes，与这个分支共享一个后背扩张的坐骨和一个长度大于宽度的跟骨。更多的近形坐骨表明在这个分支的基础位置。大部分的参考材料显示与正模的重叠很少，因此大部分没有被包括在分支系统分析中。然而，最初被描述为背肋的东西在这里被判断为股骨，与正模标本有着高度独特的形态。米洛龙的质量估计为41公斤，是石炭纪最大的合轴类之一。在彭萨科拉纪，大体型至少在斧齿目中独立演化了两次：一次在楔齿龙科，一次在剑龙科。使用系统发育比较的方法，米洛龙被发现已经独立于这两个分支进化出了大尺寸。作为石炭纪最大的恐龙之一，以及古生代最具多样性的联会动物谱系之一的外群，米洛龙代表了理解早期陆地生态系统的关键分类群。
Milosaurus mccordi was described in 1970 as a large, pelycosaurian-grade synapsid from the latest Carboniferous of Illinois but has since received little attention. Here, the holotype and referred material of Milosaurus are reexamined and incorporated into a phylogenetic analysis. Milosaurus is resolved within Haptodontiformes, sharing with this clade a posterodorsally expanded ischium and a calcaneum with greater length than width. The more plesiomorphic ischium indicates a basal position within this clade. Most of the referred material shows very little overlap with the holotype and so most was not included in the cladistic analysis. However, what was originally described as a dorsal rib is here judged to be a femur that shares a highly distinctive morphology with the holotype. With its mass estimated as 41kg, Milosaurus represents one of the largest Carboniferous synapsids. Large size evolved at least twice independently in Haptodontiformes during the Pennsylvanian: once in Sphenacodontidae and once in Edaphosauridae. Using phylogenetic comparative methods, Milosaurus is found to have evolved a large size independently of these two clades. As one of the largest Carboniferous amniotes, and the outgroup to one of the most diverse Paleozoic synapsid lineages, Milosaurus represents a crucial taxon for understanding early terrestrial ecosystems.