The 555-million-year-old worm, known as Spriggina floundersi, showcases a tendency to turn to the right, potentially providing evidence of the earliest known example of handedness.

Although these ancient organisms lacked limbs, which would prevent them from being classified as left- or right-handed in the conventional sense, the development of a directional preference implies a complex nervous system.

This behavioral trait still exists among free-roaming, nomadic species today. However, until this groundbreaking discovery, researchers believed handedness did not emerge until the Cambrian period, around 541 million years ago.

Scott Evans, a researcher at the American Museum of Natural History in New York, and his colleagues examined 100 fossilized specimens of the flatworm-like Spriggina floundersi, collected over decades in South Australia.

These ancient organisms thrived during the Ediacaran period, when multicellular life forms first became abundant. This era preceded the Cambrian explosion, a time of remarkable diversification among animal life, characterized by the appearance of various new species.

Fossils of Spriggina suggest that these creatures inhabited shallow seas approximately 500 million years ago, foraging for food on or near the ocean floor, moving in a characteristic side-to-side motion.

“We have analyzed about 50 specimens of Spriggina. The evidence indicates these fossils display a definitive curve,” said Evans. Interestingly, twice as many fossils were found curving to the left as those to the right, suggesting the original organism predominantly curved to the right due to the mirror-like preservation of its shapes.

“This finding appears statistically significant and aligns with current biologist studies on handedness across species,” explains Evans. Some specimens exhibit multiple bends on both sides, indicating their ability to bend in either direction, which is logical for avoiding circular motion while navigating.

While the majority seem to indicate right-handedness, it remains challenging to discern absolute handedness distinctions. “Imagine counting 100 people waving with one hand. You can determine that more are waving with their right hand, but you cannot definitively conclude who is right- or left-handed,” Evans elaborates.

These discoveries underscore that many fundamental traits shared among numerous modern animals, including locomotion, bilateral symmetry, and handedness, first emerged during the Ediacaran period, according to Evans.

During the Cambrian period, these early organisms built upon these fundamental traits, evolving greater complexity, such as the development of legs for more efficient movement, and gradually becoming more similar to familiar animal groups today. “This is noteworthy because it reinforces that the Cambrian, while crucial in the history of animal evolution, was not a sudden appearance of life but rather a continuation and refinement of structures established back in the Ediacaran,” Evans explains.

“The observation of handedness and its relation to functional asymmetries in the fossil record offers deep insights into the evolutionary history of these behaviors,” concludes Russell Bicknell at Flinders University in Adelaide, Australia.