Echinoderms are a major group (phylum) of invertebrate animals with a rich fossil record stretching back to the Cambrian period, approximately 518 million years ago. While all modern species are characterized by pentaradial (i.e., fivefold) symmetry, Cambrian echinoderms also include taxa with different types of symmetry (e.g., bilateral symmetry). These distinct forms were present from very early in the phylum's history, demonstrating that the initial diversification of echinoderm body plans was extremely rapid. The phylogenetic relationships of Cambrian echinoderms have long been debated, hindering efforts to reconstruct the evolution of the phylum, but recent analyses have consistently recovered bilaterally symmetrical forms as the earliest-diverging echinoderms. This reveals the sequence of character acquisition in echinoderm evolution, indicating that radial symmetry is a derived character of the group, which evolved after the acquisition of a mineralized skeleton. Cambrian echinoderms were adapted to diverse modes of life, with ecology an important factor shaping their early evolution. However, the reasons why echinoderms evolved their unique pentaradial body plan remain unclear. ▪The Cambrian fossil record provides valuable insights into the origin and early evolution of echinoderms over half a billion years ago.▪Cambrian echinoderms were morphologically diverse, with several extinct groups exhibiting character combinations that distinguish them from living species.▪Phylogenetic analyses of bilateral, asymmetrical, triradial, and pentaradial fossils have allowed us to decipher the assembly of the modern echinoderm body plan.▪Echinoderms became ecologically diverse early in their history, with varied modes of feeding, locomotion, and attachment.

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棘皮动物的起源和早期进化


棘皮动物是无脊椎动物的一个主要类群（门），其丰富的化石记录可以追溯到大约 5.18 亿年前的寒武纪时期。虽然所有现代物种都以五桡（即五重）对称性为特征，但寒武纪棘皮动物也包括具有不同类型对称性（例如双侧对称性）的分类群。这些不同的形式从该门历史的早期就存在，表明棘皮动物身体计划的初始多样化非常迅速。寒武纪棘皮动物的系统发育关系长期以来一直存在争议，阻碍了重建门进化的努力，但最近的分析始终恢复为双侧对称形式作为最早的分化棘皮动物。这揭示了棘皮动物进化中特征获得的顺序，表明径向对称性是该组的衍生特征，该组在获得矿化骨骼后进化。寒武纪棘皮动物适应了不同的生活模式，生态学是塑造它们早期进化的重要因素。然而，棘皮动物进化出其独特的五桡体计划的原因尚不清楚。▪寒武纪的化石记录为五亿多年前棘皮动物的起源和早期进化提供了宝贵的见解。▪寒武纪棘皮动物在形态上是多种多样的，几个已灭绝的类群表现出区别于现存物种的特征组合。▪对双侧、不对称、三桡骨和五桡骨化石的系统发育分析使我们能够破译现代棘皮动物身体平面的组装。棘皮动物很早就变得生态多样化。 ▪在他们的历史上，具有不同的进食、运动和依恋模式。