Homologous skeletal secretion in tommotiids and brachiopods
Homologous skeletal secretion in tommotiids and brachiopods
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DOI：
10.1130/g30323a.1
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发表时间：
2009-12-01
期刊：
影响因子：
5.8
通讯作者：
Brock, Glenn A.
中科院分区：
文献类型：
--
作者：
Balthasar, Uwe;Skovsted, Christian B.;Brock, Glenn A.
Tommotiids是早寒武世小壳动物群的独特组成部分，几乎总是由来自多元素保护盖（scleritome）的孤立磷酸盐片层代表。不寻常的范围tommotiid骨片形态和未知的结构的骨片严重阻碍了我们的理解，他们的系统发育的亲和力。然而，最近的描述罕见的，明确的scleritome材料属于tommotiid属偏心鞘属和Paterimitra支持的假设，一些tommotiids属于干组的lophophophorate门Phoronida和腕足动物，至少有一些tommotiid的骨片是同源的前体的壳的有机phytic腕足动物。在这里，我们表明，壳的微观结构的偏心鞘和Paterimitra共享大量的相似之处与paterinid腕足动物。虽然paterinids拥有一个整体的腕足动物形态，其显微结构似乎更类似于偏心鞘和Paterimitra比nonpaterinate lingulids。这些研究结果强烈支持存在的腕足动物总组，是牢固植根于tommotiids，并确定有机的骨骼组成的准晶与钙质壳的衍生。微结构的变化，建议tommotiid腕足动物的过渡可能反映了适应波动的食物和磷的摄入量，来切换到无柄的生活方式在基地的tommotiid分支。
Tommotiids are distinctive components of the early Cambrian small shelly fauna, almost invariably represented by isolated phosphatic sclerites derived from a multielement protective cover (scleritome). The unusual range of tommotiid sclerite morphologies and unknown construction of the scleritome have severely hampered our understanding of their phylogenetic affinities. However, recent description of rare, articulated scleritome material belonging to the tommotiid genera Eccentrotheca and Paterimitra support the hypothesis that some tommotiids fall within the stem group of the lophophorate phyla Phoronida and Brachiopoda and that at least some tommotiid sclerites are homologous precursors of the shells of organophosphatic brachiopods. Here we show that the shell microstructure of Eccentrotheca and Paterimitra share substantial similarities with paterinid brachiopods. While paterinids possess an overall brachiopod morphology, their microstructure appears more similar to Eccentrotheca and Paterimitra than to nonpaterinate lingulids. These findings strongly support the existence of a brachiopod total group that is solidly rooted within tommotiids, and identify the organophosphatic skeletal composition as plesiomorphic with calcareous shells as derived. The microstructural changes of the proposed tommotiid-brachiopod transition probably reflect an adaptation to fluctuating food and phosphorous intake that came with the switch to a sessile life style at the base of the tommotiid clade.