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Nature:英国学者发现最早软体动物像鼻涕虫

摘要 : 2017年2月6日,国际学术权威刊物自然出版集团《Nature》杂志在线发表了英国布里斯托大学Jakob Vinther研究员的一篇研究论文,研究人员从摩洛哥东南部挖掘的少量具有4.8亿年历史的化石显示,这些软体动物的祖先可能类似一只长有刺的蛞蝓,其头部有一个小小的脚趾甲状的壳。

2017年2月6日,国际学术权威刊物自然出版集团《Nature》杂志在线发表了英国布里斯托大学Jakob Vinther研究员的一篇研究论文,研究人员从摩洛哥东南部挖掘的少量具有4.8亿年历史的化石显示,这些软体动物的祖先可能类似一只长有刺的蛞蝓,其头部有一个小小的脚趾甲状的壳。

现在的软体动物包含诸多类型,从章鱼和牡蛎到蜗牛和蛞蝓,如此复杂的构成让科学家难以想象这些动物最古老的共同祖先看上去像什么。古生物学家将这种动物归入一个新种属Calvapilosa(拉丁文“毛茸茸的头皮”的意思)。

完整化石的长度为16.7 ~68.3毫米,不过这些碎片暗示该动物活着时至少长120毫米。研究人员近日将相关成果发表于《自然》杂志。通过分析这些化石,科学家发现了这一生物上半部(图左)长有突出的刺和壳。这些壳与现代的虾壳类似。

而它的下半部(图右)有蜗牛样的足部以便移动,并且口部长有齿舌(一种长在大多数软体动物头上用来帮助进食的器官)。这种动物齿舌的外观证实其确实属于软体动物。研究还发现它嘴里的小牙齿超过125排。考古学家推测这种10厘米长的毛茸茸生物能够用它多余的牙齿翻食物,比如覆盖着岩石的海藻。

而化石中包含的细粒砂岩表明,这块化石曾暴露在波浪或激流中,因此这种动物可能栖息在深水中。不过,软体动物大约在5.35亿年前出现,它们在寒武纪早期迅速扩张,成为了多种不同群体。研究人员指出,Calvapilosa并非该物种最古老的生物,但它因保存完好而出名,其他近亲的化石早已破碎不堪。

尽管之前有研究显示,最早的软体动物没有壳,但新成果却表明,所有软体动物的祖先可能像一条带着一个壳和很多刺的鼻涕虫。

原文链接:

Ancestral morphology of crown-group molluscs revealed by a new Ordovician stem aculiferan

原文摘要:

Exceptionally preserved fossils provide crucial insights into extinct body plans and organismal evolution1. Molluscs, one of the most disparate animal phyla, radiated rapidly during the early Cambrian period (approximately 535–520 million years ago (Ma))2. The problematic fossil taxaHalkieria3 and Orthrozanclus4 (grouped in Sachitida) have been assigned variously to stem-group annelids, brachiopods4, 5, stem-group molluscs4 or stem-group aculiferans (Polyplacophora and Aplacophora)6, but their affinities have remained controversial owing to a lack of preserved diagnostic characters. Here we describe a new early sachitid, Calvapilosa kroegeri gen. et sp. nov. from the Fezouata biota of Morocco7, 8 (Early Ordovician epoch, around 478 Ma). The new taxon is characterized by the presence of a single large anterior shell plate and polystichous radula bearing a median tooth and several lateral and uncinal teeth in more than 125 rows. Its flattened body is covered by hollow spinose sclerites, and a smooth, ventral girdle flanks an extensive mantle cavity. Phylogenetic analyses resolve C. kroegeri as a stem-group aculiferan together with other single-plated forms such as Maikhanella (Siphogonuchites) and Orthrozanclus; Halkieria is recovered closer to the aculiferan crown. These genera document the stepwise evolution of the aculiferan body plan from forms with a single, almost conchiferan-like shell through two-plated taxa such asHalkieria, to the eight-plated crown-group aculiferans. C. kroegeri therefore provides key evidence concerning the long debate about the crown molluscan affinities of sachitids. This new discovery strongly suggests that the possession of only a single calcareous shell plate and the presence of unmineralised sclerites are plesiomorphic (an ancestral trait) for the molluscan crown.

来源: Nature 浏览次数:0

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