555-Million-Year-Old Fossils Show Earliest Animal Handedness

Fossils of Spriggina floundersi from 555 million years ago provide the earliest evidence that animals favored one side of the body over the other. @NewScientist reported that Scott Evans at the American Museum of Natural History and colleagues examined 100 specimens collected in South Australia over recent decades.

The animals lived in a shallow ocean during the Ediacaran Period and foraged on or near the seafloor by wriggling left or right.

Around 50 specimens are clearly bent. Twice as many bend to the left as to the right in the fossils, indicating the living worms bent preferentially to the right. The impressions are mirror images formed when storms buried the animals in sand.

“This appears to be statistically significant and matches what biologists find when they study handedness in different animals today,” Evans said. Some specimens show multiple bends in both directions. The pattern matches handedness observed in modern animals and supplies the oldest record of functional asymmetry in any mobile organism.

Russell Bicknell of Flinders University said the presence of handedness this deep in the fossil record illuminates how such behaviors evolved. The study was published in Scientific Reports.