Department of Palaeontology, Natural History Museum, London SW75BD, UK.
Nat Commun. 2013;4:1385. doi: 10.1038/ncomms2391.
The earliest fossil echinoderms have, until now, come almost exclusively from North America and are represented by few taxa, all of which have a radiate body plan. Here we report the discovery of two new echinoderm faunas from the early part of the Cambrian of Morocco (West Gondwana). The former represents the oldest echinoderm fauna from Gondwana, approximately equivalent in age to those from North America, and the latter the oldest diversified fauna from Gondwana. In both cases, the appearance of well-preserved echinoderms coincides with a change in palaeogeographic regime. The presence of four markedly different echinoderm body plans in these earliest faunas indicates that considerable diversification had already taken place by 510 Ma. Yet all share the same distinctive biomineralized skeleton that, based on the fossil record and ocean geochemistry, probably evolved just 10-15 my earlier. This suggests that a rapid rate of morphological divergence took place during the initial stages of echinoderm evolution.
迄今为止，最早的棘皮动物化石几乎全部来自北美，且只有少数几个分类群得以代表，它们都具有辐射对称的身体形态。在这里，我们报告了在摩洛哥（西冈瓦纳）早寒武世发现的两个新的棘皮动物动物群。前者代表了冈瓦纳最早的棘皮动物动物群，其年龄与北美的动物群大致相当，后者则是冈瓦纳最早的多样化动物群。在这两种情况下，保存完好的棘皮动物的出现都与古地理环境的变化相一致。在这些最早的动物群中，有四种明显不同的棘皮动物身体形态，这表明在 5.1 亿年前已经发生了相当大的多样化。然而，所有这些动物都具有相同的独特的生物矿化骨骼，根据化石记录和海洋地球化学，这种骨骼可能在 10-15 百万年前才刚刚进化而来。这表明在棘皮动物进化的初始阶段，形态上的快速分化就已经发生了。
