Hundreds of millions of years ago, fish began to develop limbs that enabled them to walk on land. Scientists hypothesize that this ancient fish was the ancestor of mammals and humans today. The fish is known as Tiktaalik, an extinct fish-like aquatic animal 380-385 million years ago.

Now, researchers found fossils of its cousin that share similar features to Tiktaalik and have signs that it also developed limbs for walking on land. However, it also indicated that these creatures returned to full-time swimming shortly after they developed their limbs.

Paleobiologist Neil Shubin from the University of Chicago, who also co-discovered the fossil, told New York Times that perhaps evolution is more like a branching tree rather than a ladder.

Ancient Fish That Developed Legs to Walk on Land Returned to Full-Time Swimming, Study Reveals
(Photo : Wikimedia Commons/Zina Deretsky- National Science Foundation )
Life restoration of Tiktaalik roseae, a transitional fossil ("missing link") between sarcopterygian fishes and tetrapods from the late Devonian period of North America. Original description: "Fossil fish bridges evolutionary gap between animals of land and sea."

Fossils of Ancient Fish Has Fins Like A Paddle

According to Smithsonian Magazine, the fossils were first discovered 20 years ago during an expedition to the Canadian Arctic. Shubin saw a rock embedded with a fish jaw and some scales while they were eating lunch near a camp.

It took another 15 years for them to realize that the rock contains the fossils of the cousin of Tiktaalik, an ancient fish that gave important insights into the evolution of animals from sea creatures to land crawlers. The team was focused on studying Tiktallik because of its four leg-like fins that had bones resembling the human humerus, ulna, radius, and wrist.

But when they finally got to scan the ignored rock where the fossils of the cousin lie in 2020, they found an intact pectoral fin and a boomerang-shaped humerus. Researchers realized it was a fossil of an undiscovered ancient fish named Qikiqtania wakei.

The team detailed the findings of the study titled "A New Elpistostegalian From the Late Devonian of the Canadian Arctic" in the journal Nature in which they wrote that Qikiqtania might be the closest relative of Tiktaalik after it branched off from the latter. But whereas Tiktaalik would have been 9 feet, Qikiqtania was only 30 inches long.

Evolutionary biologist Richard Blob from Clemson University, who was not part of the research team, said that Qikiqtania gives a richer picture of how diverse the lifestyles of the first vertebrates that moved to land hundreds of millions of years ago.

They found that Qikiqtania did not have knobs and ridges where muscles would have been attached like Tiktaalik, and it also did not have a bendable elbow. Shubin said that it is more like a paddle that was used for swimming. Due to this, they theorize that the ancestors of Qikiqtania might have learned to walk but chose not to and returned to swimming.

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Why Did Qikiqtania Return to Swimming

According to an article in Popular Science, evolutionary biologist Thomas Stewart from Pennsylvania State University and a co-author of the study noted that their findings reveal an unexpected variation in the water-land transition of species and show diversity among animals of different kinds.

The ancient fish Qikiqtania had fins that could support their bodies, which led researchers to conclude they returned to water even after developing legs. As to why they did so, researchers could not yet give a precise answer.

However, they have few guesses explaining why Qikiqtania returned to full-time swimming. Shubin said that the meat in the water could have pushed the ancient fish to go back, given the features of its skull that indicates it can bite and suck, a powerful edge when hunting that had certain advantages in returning to the water.

However, this is not yet definitive and the team hopes to find more complete Qikiqtania specimens in the future. They hope to find a well-preserved shoulder or pelvis of the ancient fish to understand how it moved through the water.

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