Evolution Keeps Making Crabs – But a Key Feature Has Only Evolved Once

A new study of 50 true crab species suggests sideways walking evolved only once in the common ancestor of true crabs.

The trait likely appeared after the Triassic-Jurassic extinction, around 200 million years ago.

Researchers combined walking behavior with genetics to separate locomotion evolution from crab-like body-shape evolution.

Crab-like forms evolved multiple times independently, but the sideways gait was a rare shared innovation.

The finding may help explain how true crabs became one of the most successful crustacean groups.