Cambrian suspension-feeding tubicolous hemichordates.
Cambrian suspension-feeding tubicolous hemichordates.
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DOI：
10.1186/s12915-016-0271-4
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发表时间：
2016-07-07
期刊：
影响因子：
5.4
通讯作者：
Cameron CB
中科院分区：
文献类型：
--
作者：
Nanglu K;Caron JB;Conway Morris S;Cameron CB
蠕虫状肠鳃类动物的化石记录少得可怜，再加上它们与管栖翼鳃类动物的差异，使得早期半索动物的进化变得不合理。中寒武世伯吉斯页岩中的分离奥陶统曾被与环节动物、被囊动物和毛颚动物相比较，但根据丰富的新材料，现在被确定为原始的半索动物。显著特征包括兼性管栖习性、后部抓握结构和广泛的咽。这些字符，沿着与相关有机管（先前分配给绿色紫菀）中的平行排列的开口一起，证实了Oscillum是一种分层悬浮液进料器。捕食压力的增加可能是向底栖动物过渡的主要原因之一。在冠组enteroclasts这是伴随着损失的管和减少鳃杆，与相应的转变为存款喂养。后部抓握结构可能代表了翼手目匍匐茎的祖先，从而促进了它们的殖民生活方式。重点悬浮液喂养之间的基础hemichordates生活的主要模式增加了进一步的证据，悬浮液喂养的假设是主要分支Deuterostomia的祖先状态。本文的在线版本（doi：10.1186/s12915-016-0271-4）包含补充材料，可供授权用户使用。
The combination of a meager fossil record of vermiform enteropneusts and their disparity with the tubicolous pterobranchs renders early hemichordate evolution conjectural. The middle Cambrian Oesia disjuncta from the Burgess Shale has been compared to annelids, tunicates and chaetognaths, but on the basis of abundant new material is now identified as a primitive hemichordate. Notable features include a facultative tubicolous habit, a posterior grasping structure and an extensive pharynx. These characters, along with the spirally arranged openings in the associated organic tube (previously assigned to the green alga Margaretia), confirm Oesia as a tiered suspension feeder. Increasing predation pressure was probably one of the main causes of a transition to the infauna. In crown group enteropneusts this was accompanied by a loss of the tube and reduction in gill bars, with a corresponding shift to deposit feeding. The posterior grasping structure may represent an ancestral precursor to the pterobranch stolon, so facilitating their colonial lifestyle. The focus on suspension feeding as a primary mode of life amongst the basal hemichordates adds further evidence to the hypothesis that suspension feeding is the ancestral state for the major clade Deuterostomia. The online version of this article (doi:10.1186/s12915-016-0271-4) contains supplementary material, which is available to authorized users.