The advent of hard-part structural support among the Ediacara biota: Ediacaran harbinger of a Cambrian mode of body construction

Abstract

The apparent lack of taxonomic continuity between the Precambrian and Cambrian fossil records has led to controversial and conflicting interpretations about the Ediacara biota and their place in the evolution of metazoan life on this planet. This has been further complicated by the absence of similar modes of construction between these faunas and the rarity of Precambrian skeletonized fossils. We describe a new Ediacaran organism that represents the oldest multielement organism with structural support through either biomineralization or chitin. Coronacollina acula gen. et sp. nov. from the Ediacara Member (Rawnsley Quartzite) was constructed from a framework of rigid and brittle elements that disarticulated after death. It reveals a constructional mode not recognized previously among members of this assemblage, but one that was prevalent among Cambrian organisms. Coronacollina consists of a truncated cone associated with spicules, up to 37 cm in length, diverging radially from the cone. This constructional morphology is similar to the Cambrian Choia , a low conical demosponge with a corona of long spicules, providing a long-predicted constructional link between the Ediacara biota and the Cambrian fossil record.