Evans Scott D, Droser Mary L, Erwin Douglas H
Department of Paleobiology MRC-121, National Museum of Natural History, Washington, DC 20013-7012, USA.
Department of Earth and Planetary Sciences, University of California, Riverside, CA 92521, USA.
Proc Biol Sci. 2021 Feb 24;288(1945):20203055. doi: 10.1098/rspb.2020.3055.
The Ediacara Biota preserves the oldest fossil evidence of abundant, complex metazoans. Despite their significance, assigning individual taxa to specific phylogenetic groups has proved problematic. To better understand these forms, we identify developmentally controlled characters in representative taxa from the Ediacaran White Sea assemblage and compare them with the regulatory tools underlying similar traits in modern organisms. This analysis demonstrates that the genetic pathways for multicellularity, axial polarity, musculature, and a nervous system were likely present in some of these early animals. Equally meaningful is the absence of evidence for major differentiation of macroscopic body units, including distinct organs, localized sensory machinery or appendages. Together these traits help to better constrain the phylogenetic position of several key Ediacara taxa and inform our views of early metazoan evolution. An apparent lack of heads with concentrated sensory machinery or ventral nerve cords in such taxa supports the hypothesis that these evolved independently in disparate bilaterian clades.
埃迪卡拉生物群保存了丰富、复杂的后生动物最古老的化石证据。尽管它们意义重大，但将单个分类群归入特定的系统发育类群已被证明存在问题。为了更好地理解这些形态，我们识别了来自埃迪卡拉纪白海组合的代表性分类群中受发育控制的特征，并将它们与现代生物中类似特征所基于的调控工具进行比较。该分析表明，多细胞性、轴向极性、肌肉组织和神经系统的遗传途径可能存在于这些早期动物的某些种类中。同样重要的是，没有证据表明宏观身体单元存在重大分化，包括不同的器官、局部感觉机制或附肢。这些特征共同有助于更好地限制几个关键埃迪卡拉分类群的系统发育位置，并为我们对早期后生动物进化的看法提供信息。在这些分类群中明显缺乏具有集中感觉机制或腹侧神经索的头部，这支持了这些结构在不同的两侧对称动物类群中独立进化的假说。
