A CRITICAL VIEW OF ‘ANIMAL EMBRYOS’ IN THE EDIACARAN DOUSHANTUO BIOTA

Putative animal embryos in the ca. 570 Ma Doushantuo biota have taken a central role in discussions about early animal evolution and development. A diverse Ediacaran biota of sponges, diploblasts and triploblasts has been evoked on the basis of these globular fossils. Given parallel evidence for the existence of crown-group metazoans at that time, the ready acceptance of a diversity of animal embryos is perhaps not surprising. Yet doubt may be cast on all of the claims. Disregarding the many alleged embryonic features based on misinterpreted diagenetic apatite, there remains a spectrum of embryo-like fossils with genuine cellular and subcellular preservation, the interpretation of which is more exacting. None of the proposed unique metazoan characters can be upheld as autapomorphies of crown-group metazoans. The presence of nuclei falsifies recent claims that the fossils represent giant sulfur-oxidizing bacteria, but features of their behavior during mitosis suggest that that they are not crown-group metazoans either. Several lines of evidence indicate that the closest relatives are to be found further down the holozoan tree. The ‘animal embryos’ may in fact be neither animals nor embryos.