A 555-million-year-old fossil of a small, flatworm-like creature called Spriggina floundersi has provided the earliest known evidence of "handedness"—the tendency to favor one side of the body over the other. This discovery suggests that advanced nervous systems began developing much earlier than previously thought.
While these ancient worms did not have limbs and cannot be considered left- or right-handed in the modern sense, their movement patterns show a clear lateral preference. Researchers analyzed 100 fossil specimens of Spriggina floundersi, which were collected in South Australia over recent decades. These creatures lived during the Ediacaran Period, a time when multicellular life first became widespread, preceding the Cambrian explosion when animal life diversified dramatically.
By studying the fossils, Scott Evans from the American Museum of Natural History in New York and his team found that about 50 of the specimens were clearly bent. Interestingly, twice as many fossils were bent to the left than to the right. Because the fossils are mirror-image impressions formed when the animals were buried in sand during storms, this indicates that the living worms actually preferred bending to the right.
According to Evans, this distribution is statistically significant and aligns with handedness observed in modern animals. While the worms could bend both ways—which was necessary to avoid simply moving in circles—they had a clear preference for the right side.
Previously, scientists believed that such behavioral asymmetry did not emerge until the Cambrian Period, about 541 million years ago. This new finding shows that foundational animal traits, such as active movement, bilateral symmetry, and handedness, had already evolved in the Ediacaran Period. In the Cambrian Period, animals built on these existing foundations, developing legs and other complex features.
Russell Bicknell, a researcher at Flinders University in Australia, noted that finding handedness so deep in the fossil record offers valuable insights into how these complex animal behaviors originally evolved.