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.Expected final online publication date for the Annual Review of Earth and Planetary Sciences, Volume 52 is May 2024. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

中文翻译：

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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），拥有丰富的化石记录，可以追溯到大约 5.18 亿年前的寒武纪。虽然所有现代物种都具有五角对称性，但寒武纪棘皮动物还包括具有不同类型对称性（例如双边对称性）的类群。这些独特的形式从该门历史的早期就已经存在，这表明棘皮动物身体结构的最初多样化是极其迅速的。寒武纪棘皮动物的系统发育关系长期以来一直存在争议，阻碍了重建该门进化的努力，但最近的分析一致恢复了双侧对称的形式作为最早分化的棘皮动物。这揭示了棘皮动物进化中特征获得的顺序，表明径向对称是该群体的衍生特征，是在获得矿化骨骼后进化的。寒武纪棘皮动物适应了不同的生活模式，生态是塑造其早期进化的重要因素。然而，棘皮动物进化出独特的五桡体身体结构的原因仍不清楚。 ▪ 寒武纪化石记录为了解五亿年前棘皮动物的起源和早期进化提供了宝贵的见解。 ▪ 寒武纪棘皮动物形态多样，一些已灭绝的类群表现出与现存物种不同的特征组合。 ▪ 双侧、不对称、三径向和五径向化石的系统发育分析使我们能够破译现代棘皮动物身体结构的组装。 ▪ 棘皮动物在其历史早期就变得生态多样化，具有不同的进食、运动和附着方式。《地球与行星科学年度评论》第 52 卷的预计最终在线发布日期为 2024 年 5 月。请参阅 http://www.annualreviews.org/page/journal/pubdates 了解修订后的估计。