555-Million-Year-Old Fossils Show Early Rightward Bending Preference

Fossils of the flatworm-like animal Spriggina floundersi indicate a preference for turning right during movement. The specimens date to the Ediacaran Period, roughly 555 million years ago. Researchers examined 100 fossils collected in South Australia.

About 50 specimens show clear bends, with twice as many bent left as right. Because the fossils are mirror-image impressions, the pattern indicates the living animals bent right.

The study states the bending behavior is statistically significant and matches patterns of handedness observed in modern animals. Some specimens display multiple bends in both directions, suggesting the creatures could turn either way. The finding pushes back the earliest known evidence of functional asymmetry in mobile animals by tens of millions of years.

Prior estimates placed the emergence of such traits in the Cambrian Period, which began around 541 million years ago.

Spriggina lived in a shallow ocean and is thought to have foraged on or near the seafloor by wriggling. The presence of handedness indicates an advanced nervous system capable of favoring one side of the body. The same research notes that bilateral symmetry and mobility also appeared in the Ediacaran, providing foundations later expanded in the Cambrian.

A separate commentary in the paper states the discovery supplies information on how deeply in time such behaviors emerged.