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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。


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。





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


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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