EARLY ASTEROZOAN (ECHINODERNMA) DIVERSIFICATION: A PALEONTOLOGIC QUANDARY
EARLY ASTEROZOAN (ECHINODERNMA) DIVERSIFICATION: A PALEONTOLOGIC QUANDARY
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早期小星虫（棘皮动物）的多样化：古生物学的窘境
DOI：
10.1666/12-042.1
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发表时间：
2013-05-01
影响因子：
1.4
通讯作者：
Blake, Daniel B.
中科院分区：
文献类型：
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作者：
Blake, Daniel B.
传统上公认的星形动物是单系的，尽管棘皮动物的祖先是未知的。星形动物纲体星形总科最容易识别的是存在一系列简单的小听骨，称为virgals，从每个动侧小听骨向外侧延伸。Virgal系列减少到两个或三个，加上听骨特化，提供了狭窄总纲的形像（新分类）。类小行星和类蛇体的构造，以及不太像现存类的表达，在早期多样化时期出现在类蛇体中。蛇总纲和星总纲是分开的分支，其特征是虚拟系列缩小为单个听骨和其他的流动柱特化。尚不确定现存的一类或两类是直接来自某些小行星还是起源于小行星。所有三个衍生的星形动物类别都可以被认为是单系的，从而证明了类别的地位，或者要么是副系的，要么是多系的，从而表明了多种类型；在这里，单系类水平的状态有利于所有三个。
The Asterozoa as traditionally recognized is monophyletic, although ancestry within the Echinodermata is unknown. The asterozoan class Somasteroidea is most readily recognized by presence of series of simple ossicles termed virgals that extend laterally from each ambulacral ossicle. Virgal series reduction to two or three together with ossicular specializations provide apomorphies of the class Stenuroidea (new ranking). Both asteroid-like and ophiuroid-like configurations as well as expressions less suggestive of those of the surviving classes emerged within stenuroids during an early period of diversification. The classes Ophiuroidea and Asteroidea are separate lineages marked by virgal series reduction to a single ossicle and other ambulacral column specializations. It is uncertain whether one or both surviving classes were derived directly from somasteroids or originated through stenuroids. All three of the derived asterozoan classes can be argued to be either monophyletic and thereby justifying class status, or alternatively either paraphyletic or polyphyletic and thereby indicative of multiple plesions; here, monophyletic class-level status is favored for all three.