Body plan of Dickinsonia, the oldest mobile animals

Abstract

Materials collected on the territory of the southeastern White Sea area, including diversely preserved body imprints, combined body-trace fossils, specimens with signs of intravital damage and regeneration, and extended ontogenetic series, make it possible to significantly widen the data on the body plan and biology of Dickinsonia, the oldest known mobile animal, included in the Late Precambrian taxon of high rank, Proarticulata. A number of reconstructed anatomical features were added to the obvious directly observed features of Dickinsonia, such as a consistent body shape lacking lateral appendages and temporary outgrowths, transverse differentiation, and anterior–posterior polarity. These reconstructed features include dorsoventral polarity, ciliated mucus-secreting epithelium underlain by a basal lamina, two rows of blind food-gathering pockets, absence of a through-gut, nervous system of diffusive type, axial support band and muscle fibres. Such a set of features indicates the affinity of Dickinsonia and Proarticulata as a whole (the only known Ediacaran Metazoa) to Urbilateria, a hypothetical ancestor of bilaterally symmetrical animals.