550-million-year-old fossil shows earliest animal handedness

A palm-sized organism that crawled along the ocean floor more than half a billion years ago appears to have preferred turning right — making it the oldest known animal to display a population-wide side preference, according to research published today in the journal Scientific Reports.miragenews+1

Ancient Worm With a Right Turn

The study, led by researchers at the American Museum of Natural History, Florida State University, Harvard University, and the University of California, Riverside, examined more than 100 exceptionally preserved fossils of Spriggina floundersi from Nilpena Ediacara National Park and the South Australia Museum. The creature lived during the Ediacaran Period, roughly 550 million years ago, and is one of the earliest known animals with bilateral symmetry — a body plan featuring distinct front and back, left and right sides.phys+1

The team found that roughly twice as many specimens appeared bent to the left as to the right in the rock. Because the fossils preserve mirror-image impressions of the original animals, a leftward bend in stone represents an animal that bent to the right in life.miragenews+1

"When we talk about being right-or-left-handed, most people likely think about how they hold a pencil or kick a soccer ball. But our research shows that an animal without hands or feet, living over 500 million years ago, may have had its own version of handedness," said lead author Scott Evans, assistant curator of invertebrate paleontology at the Museum.miragenews

What Handedness Tells Us About Ancient Brains

The discovery carries implications beyond locomotion. In living animals, consistent side preferences are associated with complex nervous systems. Evans noted that "living animals with this sort of handedness, from insects to octopi to birds and mammals, have complex sensory abilities," suggesting that Spriggina's nervous system may have been more advanced than its ancient origins would imply.newscientist+1

"It's a reminder that some of the traits we take for granted today have incredibly ancient origins," said study coauthor Mary Droser, a paleontologist at UC Riverside.miragenews

A Window Into Early Animal Life

Spriggina is the state fossil of South Australia, named for Reg Sprigg, who first recognized the Ediacara biota in the Australian outback more than 75 years ago. The Ediacaran Period, spanning roughly 635 to 538 million years ago, marks the era when microscopic life first evolved into multicellular organisms large enough to see with the naked eye and capable of behaviors including movement. The research was supported in part by a NASA Exobiology grant.eurekalert+2