Scientists propose that recently uncovered fossils may be the earliest evidence of behavioral “handedness” in animals.
https://www.nytimes.com/2026/07/09/science/fossils-earliest-handedness-righties.html
By Jack Tamisiea
July 9, 2026See more of our coverage in your search results.Add The New York Times on Google
Are you right-handed? Roughly 90 percentof people are. But apparently the prevalence of righties is nothing even close to new: A batch of fossils from South Australia reveals that righties have had the upper hand for more than a half-billion years.
A team of researchers recently analyzed fossils of Spriggina, an organism smaller than a thumb that resembled a leech. The scientists were surprised to find that many of these fossils were bent, providing evidence that Spriggina consistently favored turning to the right as it maneuvered along the seafloor.
In a paper published on Thursday in the journal Scientific Reports, the scientists propose that Spriggina presents the earliest evidence of behavioral “handedness” in animals despite lacking anything resembling a limb.
The findings reveal that handedness is an ancient feature among complex life. “As soon as you get something that has a left and a right side, like Spriggina does, you start to see evidence of it preferring one side over the other,” said Scott D. Evans, a paleontologist at the American Museum of Natural History and the lead author of the paper.
Handedness is practically everywhere. DNA’s double helix twists to the right while the spin of particles like electrons determine whether they are right-handed or left-handed. Humans and other animals, like mice and tree frogs, exhibit behavioral handedness, or the preference to use one body side or appendage over the other. Many types of plants do, too.
Fossils provide clues that these behavioral proclivities are ancient. The earliest known evidence of handedness in the human family tree is a right-handed Homo habilis that picked at its teeth, most likely with a stone tool, around 1.8 million years ago. But behavioral handedness evolved long before even hands themselves. Scars on the right flanks of trilobite fossils reveal that these ancient arthropods usually veered to the right when trying to escape predators.
Such ancient origins illustrate the clear benefits of choosing a side, according to Loren Babcock, a paleontologist at Ohio State University who was not involved in the paper. If an animal is fleeing a predator, for instance, “time is saved if you do not have to make a decision about which foot to place first, or which way to turn,” he said.
Animals may have benefited from handedness since the Ediacaran, a geologic period that preceded the Cambrian explosion. Nilpena Ediacara National Park in South Australia preserves a snapshot of this key chapter in life’s history. More than 550 million years ago, this area was a seafloor caked in microbial mats that was home to an alien assortment of fleshy fronds, ruffled discs and spongy tubes.
Spriggina inhabited this embryonic ecosystem. The odd organism, which is South Australia’s official fossil emblem, had an elongated body of symmetrical segments that culminated in a head-like portion resembling a medieval helmet.
For decades, Spriggina was known from only a handful of fossil specimens. But paleontologists have recently excavated entire slabs from Nilpena that are full of creatures that were rapidly buried during ancient storms.
Dr. Evans and his colleagues examined several slabs that collectively contain more than 100 Spriggina specimens. Many of the fossils, which are preserved as impressions that mirror the final position of the living animal, were bent or curved as if the organism was slithering across the rock.
To understand these movements, the researchers photographed the fossils and made 3-D scans, which allowed them to measure how much the Spriggina specimens deviated from a straight line. The work revealed that Spriggina was most likely more spry than previously thought. The team thinks they wriggled their bodies like living flatworms or nudibranchs.
The team also discovered that Spriggina favored its right side. Roughly twice as many fossils represented animals bending to the right than those curving to the left. Dr. Evans warns that the fossils do not provide evidence of why Spriggina preferred to turn to the right instead of the left.
Because the animals inhabited the seafloor, it is possible that the position of their bodies may have been influenced by currents. Lidya Tarhan, a paleontologist at Yale University who was not involved in the study, however says this is unlikely. If currents swept over these Spriggina, she said, they would probably be curved in the same way instead of bent in various positions.
While Dr. Tarhan was not surprised that Spriggina could move, she said that its handedness revealed “relatively advanced sensory and motor capabilities.”
The handedness of Spriggina also connects it to much later organisms, including humans. “Specializing one side of the body is a really beneficial part of this body plan,” Dr. Evans said. “Spriggina has a front and a back and a left and right side — the same body plan that we all have.”
See more on: Scientific Reports (Journal), American Museum of Natural History
