Even before the advent of hands: an ancient limbless animal turned out to be ‘right-handed’

Scientists have studied fossils of the ancient organism Spriggina floundersi from South Australia and noticed a strange pattern: many specimens were bent to one side. Given that the imprints in the rock are preserved in mirror image, this suggests that, whilst alive, the animals probably tended to bend to the right.

If this conclusion is confirmed, it could be one of the oldest known examples of lateralisation — a preference for one side of the body — in the animal kingdom. Put simply, it is a distant evolutionary analogue of ‘right-handedness’, although Spriggina certainly did not have actual hands.

Details

Spriggina floundersi lived during the Ediacaran Period — tens of millions of years before the Cambrian ‘explosion’, when animal life began to diversify rapidly. This was a time when large multicellular organisms were already appearing on Earth, capable of movement and possessing a more complex body structure.

Spriggina is considered one of the earliest organisms to exhibit bilateral symmetry. This means that it is possible to distinguish its front and back, top and bottom, and left and right sides. This body plan later became the basis for most modern animals — from worms and insects to fish, birds and humans.

Researchers studied more than 100 well-preserved Spriggina fossils from the Nilpena site in Ediacara National Park and the collections of the South Australia Museum. These imprints are like snapshots of the ancient seabed, where the organisms were rapidly buried by sediment, probably following storms.

What exactly was found

At first glance, the discovery seems straightforward: many of the Spriggina impressions were slightly curved. But it is not the curvature itself that is important, but the direction.

Scientists discovered that roughly twice as many specimens on the rock were curved to the left as to the right. However, Ediacaran impressions preserve a mirror image of the body. Therefore, a leftward curve on the rock means that the animal itself curved to the right whilst alive.

This is precisely what makes the result interesting. If the bends were random — caused by currents, sedimentary pressure or post-mortem deformation — the scientists would have expected a more even distribution between right and left. But a consistent bias towards one side may indicate behavioural or biological asymmetry.

Why this resembles ‘right-handedness’

When we say ‘right-handed’ or ‘left-handed’, we usually mean the hand a person uses to write, eat or throw an object. But in biology, the concept is broader. Many animals show a preference for one side of their body: for example, they tend to turn in one direction, use one eye to observe an object, or use one paw to perform an action.

This is called lateralisation. It is linked to the fact that the left and right sides of the body or the nervous system may perform tasks in slightly different ways.

Why is this important?

If Spriggina did indeed bend to the right more often, this suggests that lateralisation may have emerged very early in the history of animals — even before the appearance of complex limbs, a spine, modern-type eyes and the forms of behaviour we are familiar with.

It may also suggest that the nervous or sensory organisation of such ancient creatures was more complex than a flat imprint in rock would suggest. Modern animals with a marked preference for one side often have sophisticated ways of perceiving the world and coordinating movement.

But it is important not to overinterpret here. The fossils do not reveal Spriggina’s brain and do not allow us to say exactly how its nervous system functioned. They provide only an indirect clue: the shape of its body at the time of burial was more often curved to one side.

Background

The Ediacaran Period lasted from approximately 635 to 538 million years ago. It is one of the most enigmatic stages in the history of life. During this time, large soft-bodied organisms appeared in the seas, many of which bear no resemblance to modern animals.

Fossils from South Australia are particularly important because they have preserved entire communities from the ancient seabed. Such finds allow us to study not only the form of these organisms, but also possible traces of their behaviour: how they lay, moved and interacted with their environment.

Spriggina is one of the best-known representatives of the Ediacaran biota. It is named after the geologist Reg Sprigg, who was one of the first to recognise the significance of these ancient fossils in the Australian outback.

Why this discovery is unusual

We usually think of ‘right-handed’ and ‘left-handed’ as distinctly human traits. Yet a preference for one side of the body is found in many animals: birds, mammals, octopuses and insects. New research suggests that the roots of this phenomenon may lie much deeper — in the very earliest stages of animal evolution.