One step forward, one step back for paleobiologists. Most animals are bilaterally symmetrical. They have a left and a right side. These animals form two distinct groups, protostomes and deuterostomes.

A deuterostome cambroernid fossil from the Jiangchuan Biota (~554-539 million years old). Scale bar 2 mm. Credit: Gaorong Li. These images are for editorial purposes relating to this press release ...

Our oldest known living ancestor was called a deuterostome, which gave rise to a huge swathe of life including present-day starfish and sea squirts, has been discovered fossilised in ...