Evans Scott D, Gehling James G, Erwin Douglas H, Droser Mary L
Department of Geosciences, Virginia Tech, Blacksburg, VA, 24061, USA.
South Australia Museum, Adelaide, South Australia 5000, Australia.
Paleobiology. 2022;97. doi: 10.1017/pab.2021.31. Epub 2021 Sep 13.
Constraining patterns of growth using directly observable and quantifiable characteristics can reveal a wealth of information regarding the biology of the Ediacara Biota - the oldest macroscopic, complex community forming organisms in the fossil record. However, these rely on individuals captured at an instant in time at various growth stages, and so different interpretations can be derived from the same material. Here we leverage newly discovered and well-preserved Sprigg 1947 from South Australia, combined with hundreds of previously described specimens, to test competing hypotheses for the location of module addition. We find considerable variation in the relationship between the total number of modules and body size that cannot be explained solely by expansion and contraction of individuals. Patterns derived assuming new modules differentiated at the anterior result in numerous examples where the oldest module(s) must decrease in size with overall growth, potentially falsifying this hypothesis. Observed polarity as well as the consistent posterior location of defects and indentations support module formation at this end in . Regardless, changes in repeated units with growth share similarities with those regulated by morphogen gradients in metazoans today, suggesting that these genetic pathways were operating in Ediacaran animals.
利用直接可观察和可量化的特征来限制生长模式，可以揭示出关于埃迪卡拉生物群生物学的丰富信息——埃迪卡拉生物群是化石记录中最古老的宏观、复杂的群落形成生物。然而，这些研究依赖于在不同生长阶段瞬间捕获的个体，因此相同的材料可能会得出不同的解释。在这里，我们利用新发现且保存完好的来自南澳大利亚的1947年斯普里格标本，结合数百个先前描述的标本，来检验关于模块添加位置的相互竞争的假设。我们发现模块总数与身体大小之间的关系存在相当大的差异，这不能仅通过个体的扩张和收缩来解释。假设新模块在前部分化得出的模式导致了许多例子，即最古老的模块必须随着整体生长而减小尺寸，这可能会推翻这个假设。观察到的极性以及缺陷和凹陷始终位于后部，支持了在这一端形成模块。无论如何，随着生长重复单元的变化与当今后生动物中由形态发生素梯度调节的变化有相似之处，这表明这些遗传途径在埃迪卡拉动物中发挥了作用。
