Figure 5.

Locomotor patterns in ancestral metazoans. (a,b) The evolution of nerve-net innervated longitudinal musculature from polarized conductive-contractile cells via division of labour. From Arendt et al. [37]. (c) Interpretative drawing of a Dickinsonia-like animal feeding on organic mats covering the Ediacaran seafloor ('old elephant skin'), following Evans et al. [62] and Ivantsov [63]. Fossil evidence indicates that the animals remained stationary for a period of time, removed the organic mat beneath them via external digestion or ciliary activity, and then moved from that area leaving a depression ('footprint'). Chains of footprints are interpreted as forward movement. Wrinkles on the surface indicate the presence of longitudinal muscles parallel or perpendicular to the gastric pouches (violet and red double arrows), enabling shape change. Locomotor movements may have been cilia- and musculature-driven and controlled by nerve nets.