Summary: An international team of paleontologists has uncovered the earliest known evidence of “handedness” in the animal kingdom. By analyzing over 100 exceptionally preserved fossils of the Ediacaran organism Spriggina floundersi, researchers discovered that this ancient, handless, and footless creature possessed a consistent, population-wide behavioral preference for bending to the right, revealing that lateralized nervous systems emerged far earlier in evolutionary history than previously realized.
Key Facts
- The Dawn of Bilateral Symmetry: Spriggina floundersi lived during the late Ediacaran Period (approximately 550 million years ago), a transformative era where microscopic life rapidly evolved into large, multicellular organisms. Spriggina represents one of the earliest known animals to develop bilateral symmetry, a structural body plan featuring a distinct front, back, left side, right side, top, and bottom.
- The Mirrored Bed Discovery: In examining the fossils, the team noted a surprising skew: roughly twice as many fossil impressions appeared bent to the left as to the right. Because these sandstone fossils preserve a mirror-image negative impression of the living organism, a leftward curve in the rock indicates that the physical animal preferentially bent to its right side during its lifespan.
- Population-Wide Lateralization: This distinct ratio provides definitive proof that Spriggina did not flex randomly. Instead, the population displayed a systematic behavioral bias toward rightward lateralization, cementing it as the oldest known organism with population-wide “handedness.”
- Clues to a Complex Nervous System: In modern biology, side preferences are deeply linked to brain lateralization, where different halves of the nervous system specialize in distinct tasks. Dr. Scott Evans points out that this rightward bias indicates Spriggina likely possessed a far more advanced, lateralized nervous system and complex sensory capabilities than previously credited to Ediacaran organisms.
- The Nilpena Storm Snapshots: The pristine state fossil of South Australia was preserved via ancient storm events at Nilpena Ediacara National Park, which instantly buried benthic seafloor communities in fine sediment, freezing their real-time behaviors in stone half a billion years ago.
Source: AMNH
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.
Funding: This work was supported in part by NASA Exobiology grant #80NSSC19K0472.
Key Questions Answered:
A: It comes down to a rule of fossil physics. When an animal was buried by a sudden storm 550 million years ago, it left a physical impression in the seafloor mud that later hardened into rock. This impression acts as a mirror-image negative. When Dr. Scott Evans and his team examined over 100 Spriggina fossils, they found that roughly two-thirds of the impressions were curved to the left. Because the rock preserves a reversed mirror image, a leftward bend in the stone means the living creature consistently chose to flex and turn its body to the right while crawling across the ancient seafloor.
A: In living creatures, “handedness” isn’t just an arbitrary behavioral habit, it is a physical sign of an advanced, lateralized nervous system, where the left and right halves of the brain specialize in processing different types of information. Finding a population-wide side preference in Spriggina proves that brain asymmetry isn’t a modern luxury of advanced animals. Instead, side-biased thinking evolved right alongside the very first bilateral bodies, showing that split-brain organization has been a winning survival strategy since the dawn of multicellular life.
A: The Ediacaran Period (635–538 million years ago) was a pivotal chapter in Earth’s history when life transitioned from microscopic slime into large, complex, multi-cellular organisms. Nilpena Ediacara National Park in South Australia is a world-renowned paleontological treasure because its unique rock layers preserve entire seafloor communities that were suddenly flash-frozen by underwater sandstorms. Instead of finding isolated bones, scientists uncover complete, undisturbed ecological snapshots, allowing them to study not just the shapes of ancient creatures, but their active behavioral dynamics.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- Journal paper reviewed in full.
- Additional context added by our staff.
About this evolutionary neuroscience research news
Author: Kendra Snyder
Source: American Museum of Natural History
Contact: Kendra Snyder – American Museum of Natural History
Image: The image is credited to Scott Evans / ©AMNH
Original Research: Open access.
“Earliest evidence of behavioural handedness in the Ediacaran motile bilaterian Spriggina floundersi” by Scott D. Evans, Jenson Webb, Ian V. Hughes, William Parker & Mary L. Droser. Scientific Reports
DOI:10.1038/s41598-026-53857-x
Abstract
Earliest evidence of behavioural handedness in the Ediacaran motile bilaterian Spriggina floundersi
Fossils of the Ediacara Biota preserve the oldest macroscopic communities that include animals. Classification of many of these taxa has proved contentious. Instead, studies of ecological characters reveal key insights.
Here we examine the Ediacaran fossil Spriggina floundersi from the Ediacara Member, Flinders Ranges and surrounding region. Specimens from Nilpena Ediacara National Park (NENP) and the South Australia Museum (SAM) present significant morphological variation.
Fossils found in situ on discrete bedding planes at NENP reveal no systematic orientation of features, suggesting variable morphologies formed via biological processes, rather than external forces.
Our results support motility in Spriggina, which involved bending about the long axis, propagation of pedal waves, vertical adjustment of the anterior region and horizontal manipulation of repeated body units. A significant number of fossil specimens are bent to the left (right in life).
The nature of these bends does not match expectations of anatomical asymmetry and instead constitutes the oldest described evidence of behavioural handedness. Results are consistent with Spriggina as a bilaterally symmetrical, possibly segmented, benthic organism.
These characters are unique compared with known Ediacaran ecologies but are common in various extant bilaterian groups, indicating major animal innovations prior to the Phanerozoic.
