Certain worm‐like configurations on rocks are recognized as shrinkage‐crack infillings. Some genuine Precambrian trace fossils are briefly described. The early Cambrian contains a richer assemblage, including some distinctive and widespread form genera. The study of early trace fossils leads to conclusions not only on facies, but also on the evolution of behaviour and functional morphology in soft‐bodied organisms.

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The Ediacarian, here defined as the initial period and system of the Phanerozoic Eon, is characterized by the oldest known multicellular animal life. The distinctive biotal assemblage comprises naked Metazoa, represented in the type region by 26 species in 18 genera and 4 or more phyla, plus simple metazoan surface tracks. Elements of this unique biota appeared worldwide at low paleolatitudes, following terminal Proterozoic glaciation. Ediacarian history lasted from about 670 million to 550 million years ago. This interval, plus Early Cambrian, was the time during which metazoan life diversified into nearly all of the major phyla and most of the invertebrate classes and orders subsequently known.

The earliest ‘shellly’ fossils deserve more detailed studies than they have received. Examination of the Cambrian genus Volborthella shows that it resembles in significant characters tubes of sabellariid worms, and on this basis the morphology and ecology of the animal can be reconstructed. The Cribricyathida, which include Cloudina and range from late Precambrian to lower Cambrian, are not related to Archaeoeyatha but are polychaete worm tubes with some structural characters which resemble those of serpulids. The problematic Angustiochreida (Anabarites etc.), of similar age, also show such resemblances. The first appearance in the geological record of mineralized skeletons (‘shelly fossils’), built according to various interrelated modes in annelids and in a different manner in other Metazoa, is not a suitable stratigraphic marker. The early differentiation of annelid worms can now be documented palaeontologically.