Lived 550 million years ago.. The oldest animal with a head showed a preference for its right side

- If you use your right hand for writing or performing your daily tasks, the roots of this trait may trace back to a worm-like creature that lived about 550 million years ago, which tended to bend to the right. This creature, known as "Spriggina floundersi", appeared in the seas of the Ediacaran period, which lasted from 635 to 542 million years ago, a time that witnessed the emergence of the first forms of animal life on Earth.

Its body was small, flat, segmented, and took on an elongated oval shape ending in a pointed tip on one side, while on the other side it bore a large, curved structure considered the oldest known head of an animal in the fossil record. This creature was only known through fossils discovered in what is now southern Australia.

Since the discovery of its first fossils in 1958, there has been a long debate among paleontologists about whether this creature was capable of moving on its own or if it was stationary. To resolve this dispute, a team of researchers conducted the largest study of its kind on more than 100 fossils of this creature, and their findings were published in the journal "Scientific Reports."

The study showed that "Spriggina" was not only capable of movement but also wriggled across the sea floor. It also revealed that most of its fossils were bent to the left, which means that its body, when alive, bent to the right.

The researchers saw this as an indication of a behavioral preference for using the right side, a trait that is the basis of the phenomenon of right-handedness or the predominance of right-hand use among humans and many modern animals. Although there is no living animal today that resembles "Spriggina", the researchers believe it represented an early stage in the development of lateral preference, a characteristic found in most humans, as well as in primates, mice, frogs, and some insects.

Scott Evans, the lead researcher in the study and assistant curator of the invertebrate paleontology department at the American Museum of Natural History in New York City, said: "The first animal fossils may seem very strange to most people, and even to me, but if we get past that impression, we find that many of the basic traits we associate with modern animals, such as the ability to move and even having a behavioral lateral preference, were already present in the earliest animal communities." Unexpected Discovery Researchers noted that some fossils were straight, while others appeared bent.

Since fossils are merely reverse impressions of soft-bodied organisms, the bending of the fossil to the left means that the animal, when alive, bent to the right. When comparing all samples, the team discovered that the number of fossils bent to the left was nearly double that of those bent to the right.

Evans added that this result was very surprising, as he found that the same ratio, about 2 to 1, is used today to determine lateral preference in living animals, where a larger number prefer to use the right side, explaining that "this suggests that this behavioral preference was already present in Spriggina." The researchers saw that this discovery indicates that "Spriggina" already had a nervous system connected to muscles, allowing it to bend its body in a voluntary and preferred manner, representing an important step in the evolution of animal behavior.

Diego Garcia-Bellido, a paleontology researcher at the South Australian Museum who did not participate in the study, stated that the researchers handled the evidence cautiously, examining all alternative explanations before reaching their conclusions, considering their scientific arguments to be strong and convincing. Evidence typically relies on finding fossilized traces left by animals as they crawled or moved, but "Spriggina" did not leave such traces, prompting scientists to search for other evidence.

The team began studying the anatomy of the body and noted that the organism was capable of bending in both directions, with some samples showing sharp bends resembling the letter U, indicating great flexibility in movement. However, an important question remained: Were these bends a result of the animal's own movement, or were they caused by sea waves or storms after its death?

To answer this, researchers excavated large areas of rock containing hundreds of fossils and studied the orientations of the bodies and their relationship to the effects of ocean currents. If all the fossils were oriented or bent in the same way, it would have been evidence of the influence of a single external force, such as a water current.

However, the reality was different, as the fossils were found in diverse orientations and varying degrees of bending, indicating that each organism was moving freely before being buried in the sediments. Evans stated, "We found Spriggina organisms preserved in layers that show clear signs of ocean currents, yet their bodies were not bent in the direction of those currents, nor even in the same way."

The researchers also ruled out the possibility that the bodies bent after death and drying, as the samples found in the same rock layer exhibited different shapes and orientations of bending, which is inconsistent with the effects of decay alone. Garcia-Peledo pointed out that finding Spriggina organisms fossilized close to each other, but in different positions and bends, sometimes with more than one bend in a single body, along with the presence of sediments between their bodies and the sea floor, is strong evidence that they were not anchored to the sea floor but were capable of moving freely, even if they did not leave clear signs of their movement or feeding.