Interpreting the earliest metazoan fossils: what can we learn

SYNOPSIS. The Ediacaran fossils of the latest Precambrian have at one time or another been grouped with almost every extant kingdom, and also lumped into separate kingdom-level taxa. This has often been based on the facile use of a few characters, or on some sort of "overall similarity. " This has not been a very fruit-ful approach; if anything, it has held back understanding of the Ediacaran organ-isms and of their significance for later history. While many of the simpler forms remain problematic, careful study of the more complex forms gives good reasons to place at least some of them with the Animalia. A complementary approach is to use sources of information such as the distribution of fossils across space, time, and paleoenvironments. The results may feed back into systematic work, allowing us to construct and test more robust hypotheses of these organisms ' evolutionary relationships