Kimberella quadrata is an extinct bilaterian organism from the late Ediacaran period (555 ma). It is thought to be a basal stem-group mollusc (Fedonkin & Waggoner, 1997) although its affinity to any phylum is still 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 any possible affinities between Ediacaran and Cambrian organisms because it would help resolve one of the main problems posed by the Cambrian Explosion to the Darwinian theory of evolution - a problem that Darwin himself was well aware of. The sudden appearance of complex lifeforms within the Cambrian strata begged the question "where are the ancestors of these lifeforms" The later discovery of many Ediacaran lifeforms only partly answers this question. Proving that there were forms of complex life prior to the Cambrian biota does not prove that they were related. 

Kimberella quadrata remains only partially classified.


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