Around 365 million years ago, one group of fish left the water to live on land.. These creatures were early tetrapods from which thousands of species evolved, including amphibians, birds, and humans.. But it turned out that not all of these creatures continued to live on land, some of them returned to the water, according to Science Alert..

Researchers have discovered a fossil that shows that at least one of the fish that came out on land switched back to an aquatic lifestyle.. Instead of using her fins to navigate the seabed and land, she used them exclusively for swimming..

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In 2020, scientists from the University of Chicago re-examined a fossil that was found back in 2004 in the Arctic.. Then the researchers found a jaw fragment five centimeters long with sharp teeth.. Areas of white scales of a bumpy structure were also found.. The scientists thought they were dealing with an early tetrapod, but they needed to look inside the rock where the fossils were found..

The researchers used a CT scan technique that allowed them to pass X-rays through the sample and reveal anything that was hidden from view.. As a result, they managed to find a whole fin. But the scientists were unable to complete the study as the campus was quarantined due to COVID-19..

Once the scientists were able to return to the lab, they continued their analysis.. They scanned the fin again and were able to get a closer look.. A complete analysis of the scales, jaw and fin showed that the researchers are dealing with a new species.. It also turned out that this is one of the closest relatives of vertebrates with limbs - creatures with fingers and toes.

The creature has been named Qikiqtania wakei, a name that refers to the region where the fossil was found.. The specific name was given in honor of the scientist David Wake..

The scales of the fish indicated to scientists that she lived under water. In addition, they found sensory channels that allowed the creature to sense the flow of water around.. The jaws indicated that it was a predator that held prey with its fangs.. But most of all, scientists were surprised by the pectoral fin of Qikiqtania, it had a humerus, like a human shoulder, but it had a peculiar shape..

Early tetrapods had humeral fins with a prominent ridge on the underside and a characteristic set of bulges to which muscles were attached.. Such muscles are evidence that early tetrapods lived at the bottom of lakes and streams, using their fins or arms to support themselves, first on land under water and then on land..

But the Qikiqtania humerus was different, lacking the characteristic ridges and processes. But it was thin and resembled a boomerang shape, the remaining part of the fin was large and paddle-shaped.. This fin was designed for swimming.

Scientists believe these signs indicate that this ancient fish has returned from land to live in the water again..

Earlier, scientists conducted a new study of fossils that include the brain and nervous system of Stanleycaris hirpex creatures that lived on Earth 500 million years ago.. They came to the conclusion that these creatures can change the existing ideas about the evolution of insects and arthropods..