About 555 million years ago

The Garden of Ediacara

A tiny soft body with a front and a back, creeping over a sea floor carpeted in microbes.

From the game. The art is a reconstruction.

The first bodies with a direction

Bilaterians are animals with a left and right side, and a front and back. They include worms, insects, fish and us. The body in this era is inspired by Ikaria wariootia, a fossil from South Australia described in 2020 as one of the oldest known bilaterians.

What the evidence shows

Ikaria was small and simple, about the size of a grain of rice, with a distinct front and back end.
Its size and shape match the predicted maker of burrow traces found in the same rocks, suggesting an animal that moved through sediment.
Those traces appear below the classic Ediacaran body fossils in the rock sequence.

What is reconstructed

How Ikaria fed, sensed and reproduced is not preserved.
Whether Ikaria is on our line or a close cousin of it is unknown.

Sources

Evans et al. 2020. Discovery of the oldest bilaterian from the Ediacaran of South Australia. PNAS. (opens the publisher’s site)
What it supports: Ikaria wariootia: a small, simple animal with a distinct front and back, matching the predicted maker of nearby burrow traces. It is not a proven direct ancestor.

Summaries here are our own. Some publishers limit access to full papers; learning on this site is never paywalled.