Fossils of Spriggina floundersi collected in South Australia. 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.Scott Evans/© AMNH
It didn’t have limbs, but an extinct marine animal that lived more than half a billion years ago provides what may be the earliest evidence of “handedness” in the animal kingdom.
New research published today in the journal Scientific Reports suggests that that the tiny, segmented organism Spriggina floundersi showed a consistent preference for bending to the right as it navigated the sea floor. In other words, it was right-handed.
“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 the study’s lead author Scott Evans, an assistant curator of invertebrate paleontology at the Museum.
Spriggina is one of the earliest known animals with bilateral symmetry, a body plan defined by distinct front and back, left and right sides, and top and bottom. This fundamental body arrangement is shared by humans and the vast majority of animals living today. It lived during a transformative time known as the Ediacaran Period (about 635–538 million years ago), when microscopic life evolved to become multicellular, large enough to see with the naked eye, and capable of increasingly complex behaviors, including movement.
Stretching just a few centimeters in length, Spriggina had a horseshoe-shaped head and an elongated body with overlapping segments arranged in a chevron pattern. The state fossil of South Australia, Spriggina specimens are exceptionally preserved in the Flinders Ranges, where Evans and colleagues examined shape variation in more than 100 fossils of this species from Nilpena Ediacara National Park and the collections of the South Australia Museum in Adelaide.
The team discovered that about twice as many Spriggina 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.
The findings suggest that left-right asymmetry in animals evolved earlier than previously recognized.
“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 also say the discovery also provides new insight 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.”