Although very few of the Ediacaran macrobiota can be assigned to modern animal groups with any certainty, there are several reasons to suspect that animals were present, and quite diverse, during the late Ediacaran Period.
Trace fossils provide evidence of motile, presumably muscular animals moving around and potentially even feeding on the Ediacaran sea floor. These would suggest that organisms of cnidarian or bilaterian-grade were present by this time.
Further arguments come from biomarkers (chemical 'fossils' that record signatures of specific modern animal groups, such as some sponges, in ancient rocks; Love et al., 2009), and from molecular clocks, which widely predict that animals originated in the Cryogenian Period, ~700 Ma, and that most of the divergences between major animal phyla took place during the Ediacaran Period (e.g. Erwin et al., 2011; dos Reis et al., 2015).
Fossil evidence for metazoans
Several Ediacaran macrofossils have been proposed as candidate animals in recent years, with varying degrees of acceptance in the scientific literature. These include the possible sponges Coronacollina, Palaeophragmodictya, and Thectardis; the possible mollusc Kimberella; and the potential cnidarians Haootia, Corumbella, and ...
Claims for more complex groups, such as ascideans (REF), echinoderms (REF), annelids (REF) and ... have received less support.
The problem in all cases is that modern animal phyla diagnostically possess a suite of morphological characters, many of which are not observed in Ediacaran fossils, and some of which are unlikely to ever have been preserved (for example the nematocysts of modern cnidarians). As such, although a fossil may possess some of the diagnostic characters of a modern animal group, very few possess them all, and we therefore cannot be certain that they belong to a particular group. Furthermore, the possibility exists that many of the fossils may represent stem group members of modern animal taxa. In such instances, we would only expect them to possess a limited range of the characters diagnostic of the modern group, but often this limited character suite can be shared by multiple modern groups. We also cannot rule out the possibility that the fossils represent groups that have since entirely gone extinct.