This 550-Million-Year-Old Animal Already Had Favorite Way to Turn

Long before anyone argued about being left-handed or right-handed, a small, worm-like animal was crawling across the ancient seafloor with a clear preference for which way to turn. Scientists now have the fossils to prove it.

Researchers studying a mysterious creature called Spriggina floundersi, a centimeter-long organism that lived roughly 550 to 560 million years ago, say they have found the oldest known evidence of behavioral handedness in the fossil record. Writing in the journal Scientific Reports, the team explains that this animal tended to turn in one direction more than the other, much like a person who favors one hand for writing. That habit shows up hundreds of millions of years before the Phanerozoic burst of animal diversity, the period often treated as the true starting line for the animal kingdom.

Spriggina belongs to the Ediacara Biota, the oldest fossil communities known to include animals. These creatures lived long before the first dinosaurs, and researchers have argued for decades about what many of them were and whether they could even move. A turning preference suggests something bigger than movement alone: a trait tied to a fairly capable nervous system, present far earlier than the fossil record had shown.

A Right-Turning Habit at the Dawn of Animal Life

Spriggina was a flat, elongated creature with a wider front end and a tapering tail, its body divided into repeating segments lined up on either side of a central ridge. It lived on the ocean floor in what is now South Australia, preserved in rock layers that rank among the best windows scientists have into early animal life. For decades, the argument circled one basic question: could this thing move on its own?

How the Fossils Revealed Spriggina’s Behavioral Handedness

To answer that, a research team examined more than 100 fossil specimens, including animals preserved right where they died in individual rock layers at Nilpena Ediacara National Park, as well as specimens held at the South Australian Museum. Careful measurements of each fossil’s bends, lifted edges, and body features produced the clearest picture yet of how Spriggina moved.

About 70 percent of specimens were bent along their length, curving to one side. Counting those bends turned up a lopsided result: roughly twice as many curved left as curved right. Because these fossils preserve a mirror image of the living animal, a leftward bend in the rock means a rightward turn in life. A statistical test put the odds of that being random very low (p = 0.0017), well past the bar scientists use to call a result meaningful.

Ruling Out Currents and Body Shape

Before calling this a behavior, the team considered simpler explanations first. Could ocean currents have pushed the bodies into matching curves? Evidence says no. On two large excavated surfaces, Spriggina specimens pointed in every direction with no shared alignment. On one of them, currents had clearly nudged other nearby creatures, yet Spriggina showed no matching pattern, and animals sitting inches apart curved in opposite directions.

A built-in body quirk was the other candidate, the way a corkscrew always spirals the same direction because of its shape. That does not fit either. An animal with that kind of fixed lopsidedness would have nearly every individual bending the same way. Here, most turned right while a real share turned left, the fingerprint of a behavioral tendency rather than a mechanical one. Living animals such as ants, bumblebees, and giant water bugs show a milder version of the same thing, a turning bias present in what the authors call “a significant but not overwhelming majority of individuals.” Spriggina fit that description.

Why Behavioral Handedness Matters for Early Animals

Handedness was not Spriggina‘s only talent. Fossils show an animal that could bend side to side, ripple wave-like motions along its outer edges the way flatworms and sea slugs do today, lift its front end off the seafloor, and shift its body segments independently. Some specimens are missing chunks of their outer margins, which the team interprets as spots where the creature had raised part of itself off the mud while buried. Its flat build and consistent right-side-up preservation point to a bottom-dweller, though it may have occasionally lifted its whole body and swum just above the seafloor, as some marine flatworms do now.

One absence stood out. Spriggina left no sign of disturbing the slimy microbial mats that carpeted the Ediacaran seafloor, unlike neighbors that plowed through them to feed. How it fed remains an open question, though its diet likely operated differently.

Handedness carries the most weight for evolution. A turning preference across a whole population hints at a nervous system more capable than anyone expected this early, and Spriggina is the only Ediacaran animal known to show one. A separate look at Dickinsonia, another mobile Ediacaran creature, found roughly equal left and right turns and no preference at all. This work also revisits body segmentation, the repeating-unit plan shared by insects, worms, and backboned animals. Spriggina‘s units exhibit a few features consistent with true segmentation, which would make them the oldest on record, though the authors stress that the evidence cannot confirm this yet.

What the rock ultimately records is that the small biases that shape how animals move did not arise alongside big brains. Half a billion years ago, something small was already turning right.