Scientists have uncovered what may be the earliest evidence of "right-handedness" in the animal kingdom, dating back more than half a billion years.
The discovery comes from the fossil record of Spriggina floundersi, an organism from the Ediacaran Period that lived about 550 million years ago. New research published today in the journal Scientific Reports and led by researchers at the American Museum of Natural History, Florida State University, Harvard University, and the University of California, Riverside indicates that Spriggina showed a consistent preference for bending to the right.
The findings provide a remarkable glimpse into the origins of left-right asymmetry in animals, suggesting that behavioral preferences associated with one side of the body emerged far earlier in evolutionary history than previously recognized.
"When we talk about being right-or-left-handed, most people likely think about how they hold a pencil or a 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.
The Ediacaran Period (about 635–538 million years ago) marks one of the most transformative chapters in the history of life on Earth. During this time, microscopic life evolved to become multicellular, large enough to see with the naked eye, and capable of increasingly complex behaviors, including movement.
The Flinders Ranges and surrounding region of South Australia preserves one of the most exceptional records of this fossil assemblage known from this time. In particular, excavation of individual beds at Nilpena Ediacara National Park reveals communities of the Ediacara biota buried during storm events, capturing snapshots of the seafloor 550 million years ago.
Among the fossil organisms recorded there is Spriggina, one of the earliest known animals with bilateral symmetry—a body plan featuring a distinct front and back, left and right sides, and top and bottom. This same basic body organization is shared by humans and most animals alive today. Spriggina is the state fossil of South Australia and is named for Reg Sprigg, who first recognized the Ediacara biota in the Australian outback more than 75 years ago.
To investigate whether Spriggina exhibited any left-right preference, researchers examined shape variation in more than 100 exceptionally preserved fossils from the fossil beds at Nilpena and from the collections of the South Australia Museum in Adelaide.
The team made a surprising discovery: roughly twice as many specimens appeared bent to the left as to the right. Because these fossils preserve mirror-image impressions of the original animals, a leftward bend in the rock represents an animal that bent to the right in life.
This consistent pattern suggests that Spriggina preferentially turned to the right, making it the oldest known animal to display population-wide "handedness."
"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 the University of California, Riverside.
The researchers say the discovery also provides new clues about how Spriggina might have perceived the world.
"We know that living animals with this sort of handedness, from insects to octopi to birds and mammals, have complex sensory abilities." Evans said. "So this may be telling us that the nervous system of Spriggina was relatively complex and more similar to those of animals that we know today."
Other authors on this study include Jenson Webb from Florida State University and the Florida Department of Environmental Protection; Ian V. Hughes from Harvard University; and William Parker from Florida State University.
This work was supported in part by NASA Exobiology grant #80NSSC19K0472.
Study DOI: 10.1038/s41598-026-53857-x
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