中国科学院南京地质古生物研究所机构知识库

Embryo-like fossils from the early Ediacaran Weng'an Biota (SW China, 609 myr ago), widely interpreted as holozoans, potentially provide insights into the early evolutionary development of metazoans and the rise of the animal kingdom. However, the biodiversity of the embryo-like fossil assemblage is largely underestimated and its more precise phylogenetic affinities within the holozoan tree are still under debate. We describe a new species of embryo-like fossil, Ostiosphaera rara n. gen. n. sp., from the Ediacaran Weng'an Biota. These 3D, phosphatized specimens exhibit a spherical morphology, a thick ornamented envelope with a circular opening and a membrane-bound, multicellular inner body. In terms of biological characteristics, O. rara shows similarities with a number of extant and fossil analogues, including testate amoebae, unicellular green algae, the cellular slime mould Fonticuida and co-occurring Weng'an embryo-like fossils. Although the phylogenetic affinity of O. rara is difficult to constrain precisely based on the available evidence, it is reasonable to follow the holozoan interpretation for these fossils because they share the same grade complexity with co-occurring embryo-like fossils, such as Megasphaera and Helicoforamina, in terms of the combination of biological features. These new holozoans resemble asexual reproductive gemmules of fossil and living demosponges in size, morphology, circular opening and cellular anatomy. If this similarity reflects biological affinity rather than convergent evolution, this discovery would force us to rethink the evolutionary history of Precambrian sponges.& nbsp;& nbsp;