They became extinct shortly after the so-called Cambrian explosion, with the introduction of fauna forming groups more recognizably related to modern animals, however sponges may be descended from this clade.

The hypothesis was formulated by the German geologist Adolf Seilacher, who even doubts its relationship with the animal kingdom, or its multicellular nature — the group might have originated independently, and could be large unicellular forms.

The Ediacarans' abundant preservation is surprising, despite having soft bodies; this almost surely indicates the absence of burrowing creatures in their home sediments.

The presence of numerous streaks, folds or segments considerably increases the total surface area, necessary for the osmotic absorption of nutrients.

The first to appear were frondomorphs (Petalonamae) and simple medusoids 578 Ma (millions of years) ago and are considered the oldest complex life forms.

Those who see here different unrelated groups, place the proarticulates in Bilateria basally (this opinion is the most upheld among these alternative theories) or as pre-arthropods, the petalonams with cnidarians such as sea pens or as ctenophores, and the trilobozoa and medusoids are considered jellyfish without cnidoblasts and classified in Cnidaria or Coelenterata.

It has been suggested that vendobionts may come from amoeboid protozoa or protists, and be, for example, similar to xenophiophores,[12] which are unicellular foraminifera that have developed large size, reaching 20 cm.

[1] However, structural studies of these fossils have so far revealed no traces of a shell, testa or carapace organic material (sclerotized), agglutinated or mineralized, the presence of which is implicit in this hypothesis.

The structural simplicity of the impressions of existing Ediacaran and cnidarians suggests that their mutual similarities may be due to convergence; however, possible phylogenetic affinities between them cannot be completely ruled out.

[17] There are morphological differences between the jellyfish and their globose and gelatinous shape, compared to the flat, discoid medusoids, with relief that is greater on the dorsal side and firmer due to the indications that would reveal the existence of a rigid wall surrounding the body .

It can be suggested that there is no evidence that medusoids share biological characteristics with coelenterates; there is no mouth, no two-layered body wall enclosing a single cavity.

This, and the evidence for a rigid outer wall, adds to recent doubts about the concept of an Ediacaran fauna that would have been dominated by soft-bodied coelenterates.

However, other anatomical features of the proarticulates, mainly the absence of truly complete segmentation, articulated limbs, and any other lateral processes, do not agree with this interpretation.