The functional head of the Cambrian radiodontan (stem-group Euarthropoda) Amplectobelua symbrachiata.
The functional head of the Cambrian radiodontan (stem-group Euarthropoda) Amplectobelua symbrachiata.
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寒武纪放射齿动物（真节肢动物干群）Ampletobelua symbrachiata 的功能头部
DOI：
10.1186/s12862-017-1049-1
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发表时间：
2017-08-30
影响因子：
3.4
通讯作者：
Hou X
中科院分区：
文献类型：
--
作者：
Cong P;Daley AC;Edgecombe GD;Hou X
真节肢动物干群头部的体节组成和同源性一直是近期节肢动物起源研究的焦点。一个新出现的假说认为，上干群真节肢动物拥有一个三节的头部/大脑，包括一个眼节（原脑），其后是带有相关触角/捕食肢的中脑以及后脑，而在干群基部，放射齿目（Radiodonta）的头部结构完全与原脑及其前部相关。然而，这一假说尚未经过充分验证，因为关于放射齿目头部组成的详细知识尚不完整，而且许多分类群缺乏能提供信息的完整标本。短棒状奇虾（Amplectobelua symbrachiata）是澄江生物群（约5.2亿年前）中最常见的放射齿目物种，通常只知道其孤立的额附肢。在此，我们对新的完整标本进行详细描述，阐明其头部结构的形态和功能，并讨论它们对真节肢动物头部组织假说的影响。
除了一个中央椭圆形的头盾，短棒状奇虾还具有一对由细长杆连接的P元件。其口由多组光滑和具结节的板组成，这与其他放射齿目的典型放射状口锥不同。先前确定的“掌状齿”位于头部后部的口外部，被解释为体节状的颚基样结构（GLSs），与至少三个退化的过渡瓣以一对一（对）的模式相关联，这与附肢的性质相符。与其他泛节肢动物的比较表明，GLSs在形态上与真节肢动物的下颚和其他颚基口器以及有爪动物的颚相似，表明它们在短棒状奇虾的进食活动中具有功能整合性。
短棒状奇虾的功能性头部必须包括退化的过渡体节（及其相关结构），这些在其他几个放射齿目中也已被发现。这种功能性观点支持这样一种观点，即体节（及相关附肢）整合到头部区域，可能是由进食驱动的，这种情况在真节肢动物干群谱系中发生。然而，不同类群之间退化过渡体节的数量各不相同，而且GLSs代表附肢的近端还是远端部分仍不确定。我们的研究首次描述了放射齿目功能性头部区域中除额附肢之外的附肢结构，揭示了真节肢动物从干群基部到上部在形态转变过程中的新型进食结构。
Segmental composition and homologies of the head of stem-group Euarthropoda have been the foci of recent studies on arthropod origins. An emerging hypothesis suggests that upper-stem group euarthropods possessed a three-segmented head/brain, including an ocular segment (protocerebrum) followed by the deutocerebrum with associated antennae/raptorial limbs and the tritocerebrum, while in the lower stem, head structures of Radiodonta are wholly associated with the protocerebrum and its preceding part. However, this hypothesis is incompletely tested because detailed knowledge on the head components of radiodontans is patchy, and informative articulated specimens are lacking for many taxa. Amplectobelua symbrachiata is the most common radiodontan species in the Chengjiang biota (ca. 520 Ma), normally known as isolated frontal appendages. Here we present detailed descriptions of new articulated specimens that elucidate the morphology and function of its head structures, and discuss their implications for hypotheses about euarthropod cephalic organisation. In addition to a central oval head shield, A. symbrachiata also bears a pair of P-elements connected by an elongated rod. The mouth consists of sets of smooth and tuberculate plates, in contrast to the typical radial oral cones of other radiodontans. Previously identified ‘palm-like teeth’ are located external to the mouth in the posterior head region, and are interpreted as segmental gnathobase-like structures (GLSs) associated with at least three reduced transitional flaps in a one (pair)-to-one (pair) pattern, consistent with an appendicular nature. Comparisons with other panarthropods show that GLSs are morphologically similar to the mandibles and other gnathobasic mouthparts of euarthropods, as well as to the jaws of onychophorans, indicating their functional integration into the feeding activities of A. symbrachiata. The functional head of A. symbrachiata must include the reduced transitional segments (and their associated structures), which have been identified in several other radiodontans. This functional view supports the idea that the integration of segments (and associated appendages) into the head region, probably driven by feeding, occurred along the euarthropod stem-lineage. However, the number of reduced transitional segments varies between different groups and it remains uncertain whether GLSs represent proximal or distal parts of appendages. Our study is the first description of appendicular structures other than the frontal appendages in the functional head region of radiodontans, revealing novel feeding structures in the morphological transition from the lower- to the upper- stem-group of Euarthropoda.
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影响因子：
1.4
作者：
Collins, D
通讯作者：
Collins, D
早寒武世澄江生物群放射齿象Lyrarapax的形态
影响因子：
1.4
作者：
Cong, Peiyun;Daley, Allison C.;Chen, Ailin
通讯作者：
Chen, Ailin
影响因子：
2.6
作者：
Daley, Allison C.;Paterson, John R.;Jago, James B.
通讯作者：
Jago, James B.
影响因子：
56.9
作者：
CHEN, JY;RAMSKOLD, L;ZHOU, GQ
通讯作者：
ZHOU, GQ
影响因子：
2.6
作者：
Daley, Allison C.;Budd, Graham E.
通讯作者：
Budd, Graham E.