Earth, Ocean, and Atmospheric Sciences, Florida State University, Tallahassee, Florida, USA.
Organismic and Evolutionary Biology, Harvard, Cambridge, Massachusetts, USA.
Evol Dev. 2024 Nov;26(6):e12491. doi: 10.1111/ede.12491. Epub 2024 Sep 3.
Fossils of the Ediacara Biota preserve the oldest evidence for complex, macroscopic animals. Most are difficult to constrain phylogenetically, however, the presence of rare, derived groups suggests that many more fossils from this period represent extant groups than are currently appreciated. One approach to recognize such early animals is to instead focus on characteristics widespread in animals today, for example multicellularity, motility, and axial polarity. Here, we describe a new taxon, Quaestio simpsonorum gen. et sp. nov. from the Ediacaran of South Australia. Quaestio is reconstructed with a thin external membrane connecting more resilient tissues with anterior-posterior polarity, left-right asymmetry and tentative evidence for dorsoventral differentiation. Associated trace fossils indicate an epibenthic and motile lifestyle. Our results suggest that Quaestio was a motile eumetazoan with a body plan not previously recognized in the Ediacaran, including definitive evidence of chirality. This organization, combined with previous evidence for axial patterning in a variety of other Ediacara taxa, demonstrates that metazoan body plans were well established in the Precambrian.
埃迪卡拉生物群的化石保存了最古老的复杂宏观动物的证据。然而，大多数化石在系统发育上都很难确定，但是一些罕见的衍生类群的存在表明，这个时期的许多化石代表的是现存的生物群，而不是人们目前所认为的那样。一种识别这些早期动物的方法是，转而关注今天动物中广泛存在的特征，例如多细胞性、运动性和轴向极性。在这里，我们描述了来自南澳大利亚埃迪卡拉纪的一个新的分类单元，Quaestio simpsonorum 属和种。Quaestio 被重建为具有薄的外部膜，将更有弹性的组织与前后极性、左右不对称性以及潜在的背腹分化联系起来。相关的痕迹化石表明它是一种底栖和运动的生活方式。我们的研究结果表明，Quaestio 是一种能动的真后生动物，其身体结构在埃迪卡拉纪以前从未被识别过，包括手性的明确证据。这种组织形式，加上以前在各种其他埃迪卡拉分类群中发现的轴向模式的证据，表明后生动物的身体结构在前寒武纪就已经很好地建立起来了。
