Japanese researchers have traced the iconic sideways walk of crabs to a single evolutionary event that occurred approximately 200 million years ago [1].

This discovery provides a critical link in understanding how crustaceans adapted to survive and diversify following the Triassic-Jurassic extinction. By identifying a common ancestor for this movement, scientists can better map the evolutionary trajectory of marine life during the early Jurassic period.

The team conducted their study by observing 50 different crab species [2]. Among these, 35 species were identified as sideways walkers, while 15 species walk forward [2]. The data suggests that the sideways gait did not evolve multiple times across different lineages, but rather emerged once and was passed down through generations.

Researchers focused on species found in Japanese waters to analyze locomotion patterns. The findings indicate that this specific method of movement provided a distinct survival advantage, allowing crabs to navigate their environments more effectively than their predecessors.

This evolutionary shift coincided with a period of global biological recovery. The ability to move sideways likely helped the species thrive in diverse niches, contributing to the wide variety of crab species seen in the oceans today [1], [3].

“The sideways walk of crabs [traced] to a single evolutionary event that occurred about 200 million years ago.”

The identification of a single evolutionary origin for sideways walking simplifies the phylogenetic understanding of crabs. It suggests that a specific anatomical mutation or behavioral shift provided such a significant competitive edge during the early Jurassic that it became a dominant trait, ultimately shaping the biological success of the group across global marine ecosystems.