Kimberella quadrata is an extinct bilaterian organism from the late Ediacaran period (635 -542 Mya). It grew up to 150mm in length and is thought to be a stem-mollusc (Fedonkin & Waggoner, 1997) although this affinity is not agreed upon.

Kimberella had an ovate shell-like cap that was non-mineralised and flexible.The surface of the cap was covered in hardened raised nodules that are thought to have been anchor points for an array of dorso-ventral muscles that extended down to a single muscular "foot". A ripple wave motion through the foot enabled movement.

An extensive frill-like structure radiated out from beneath the central cap and this is thought to have functioned like an oxygenating gill.

No feeding appendage has been discovered for Kimberella but scrape marks found in association with fossil remains (Gehling et al., 2014) suggest Kimberella had a proboscis type appendage - similar to a modern snail's radula - that it used to gather and eat nutrients. This in turn suggests the development of a rudimentary gut system.

It is important to tease out the affinities between Ediacaran and Cambrian organisms because it would help resolve "Darwin's Dilemma". This dilemma refers to the sudden appearance in the Cambrian geological record of so many complex and varied lifeforms which represent all modern animal body-plans or Phylum. This presented a problem for Darwin's theory of evolution. This sudden appearance of complex lifeforms within the Cambrian strata begged the question "where are the ancestors of these lifeforms?"

The discovery of many Precambrian lifeforms since Darwin's lifetime has largely resolved Darwin's dilemma although affinities between those lifeforms and the ones that followed are still to be agreed upon.

Paleozoo button by Bruce Currie

With thanks to Prof. Jim Gehling for feedback on anatomical detail.