Spriggina flounder is an ancient marine species that thrived during the Ediacaran period, around 550 million years ago. This organism stands as one of the earliest bilaterally symmetrical animals documented on Earth. Recent studies analyzing over 100 newly discovered fossils in South Australia indicate that left-right behavioral preferences appeared much earlier in evolutionary history than previously believed.
Fossil of Spriggina flounder from South Australia. White arrows indicate raised regions, and white triangles show bending angles of adjacent modules. Scale bar – 10 cm. Image credit: Evans et al., doi: 10.1038/s41598-026-53857-x.
The Ediacaran period (635 to 538 million years ago) represents a pivotal era in Earth’s evolutionary history.
During this transformative time, life transitioned from microscopic organisms to multicellular forms visible to the naked eye, exhibiting complex behaviors, including locomotion.
The Flinders Ranges in South Australia preserve an exceptional fossil record from this era, particularly at the Nilpena-Ediacaran National Park, where layers of Ediacaran communities were buried during storms, providing a glimpse into the ancient ocean floor.
Among the fossils uncovered is Spriggina flounder, initially described in 1958 based on three specimens. This species is significant as one of the earliest known entities to display bilateral symmetry—a body structure featuring distinct left, right, top, and bottom sides.
This fundamental design is shared by humans and most contemporary animals.
As Dr. Scott Evans, a paleontologist from the American Museum of Natural History and Florida State University, notes, “Discussions about being right-handed or left-handed usually relate to tasks like writing or kicking a ball. Our research indicates that even ancient animals, like those from over 500 million years ago, may have exhibited their own version of handedness.”
To explore lateral preferences in Spriggina flounder, researchers analyzed the shapes of over 100 well-preserved fossils from the Nilpena Fossil Bed and collections at the South Australian Museum in Adelaide.
They made a groundbreaking observation: approximately twice as many fossils exhibited leftward bends compared to those bent right.
These fossils retain a mirror image of the original organisms, suggesting that the leftward bends indicate creatures that bent right while alive.
This consistency implies that Spriggina flounder tended to favor a rightward orientation, marking it as the oldest known animal to exhibit “handedness.”
Dr. Mary Droser, a paleontologist at the University of California, Riverside, affirms, “This finding highlights that several traits we consider modern have deep evolutionary roots.”
The insights gained also hint at how Spriggina flounder interacted with its environment.
“Living creatures with this type of handedness—like insects, octopuses, birds, and mammals—possess advanced sensory abilities,” Dr. Evans adds. “This suggests that the nervous system of Spriggina flounder was relatively intricate and resembled that of modern animals.”
These results were published in the Journal of Scientific Reports on July 9, 2026.
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Evans et al. 2026. Earliest evidence for behavioral handedness in Ediacaran motile bilateral animals: Spriggina flounder. Scientific Reports 16, 19924. doi: 10.1038/s41598-026-53857-x
Source: www.sci.news
