One of the first animals to walk on land immediately returned to the water

(ORDO NEWS) — Approximately 365 million years ago, one group of fish left the water to live on land.

These animals were early tetrapods, a genus that included many thousands of species, including amphibians, birds, lizards, and mammals. Humans are the descendants of these early tetrapods, and we share the legacy of their transition from water to land.

But what if, instead of making landfall, they turned back? What if these animals, as soon as they left the water, retreated to live again in more open waters?

New fossils suggest that one fish did just that. Unlike other closely related animals that used their fins to support their bodies at the bottom of the water and may have ventured onto dry land occasionally, this newly discovered creature had fins designed for swimming.

In March 2020, I worked at the University of Chicago in the laboratory of biologist Neil Shubin. I worked with Justin Lemberg, another researcher in our group, on the processing of a fossil collected in 2004 during an expedition to the Canadian Arctic.

On the surface of the rock in which it was embedded, fragments of jaws about 2 inches (5 cm) long and with sharp teeth were visible. Areas of white scales with a bumpy texture were also visible. The anatomy gave us subtle hints that the fossil was an early tetrapod. But we wanted to look inside the stone.

So we used a technique called computed tomography, in which X-rays penetrate the sample to find anything that might be hidden inside, out of view.

On March 13, we scanned an inconspicuous piece of rock with a few scales on top and found that there was a whole fin inside it. Our jaw dropped. A few days later, the lab and campus closed, and COVID-19 sent us into isolation.

Such a fin is extremely valuable. It could give scientists clues about how early tetrapods evolved and how they lived hundreds of millions of years ago. For example, the shape of certain bones in the skeleton can predict whether an animal was swimming or walking.

Although the first scan of the fin was promising, we needed to see the skeleton in high resolution. As soon as we were allowed to return to campus, a professor in the geophysical sciences department at the university helped us cut the block with a stone saw.

Thus, there was more fin and less stone in the block, which made it possible to make a better scan and take a closer look at the fin.

When the dust cleared and we finished analyzing the jaw, scale and fin data, we realized that this animal was a new species. Moreover, it turned out that this is one of the closest known relatives of vertebrates with limbs – creatures with fingers and toes.

We named it Qikiqtania wakei. Its generic name, pronounced “kik-kik-tani-ahh”, refers to the Inuktitut words Qikiqtaaluk or Qikiqtani, the traditional name for the region where the fossil was found.

When this fish was alive, many hundreds of millions of years ago, it was a warm environment with rivers and streams. Its specific name honors the late David Wake, a scientist and mentor who inspired many of us in the fields of evolutionary and developmental biology.

Skeletons tell about how the animal lived

Kikiktania tells a lot about the most important period in the history of our family. Its scales unambiguously tell researchers that the animal lived underwater. They show sensory channels that allowed the animal to sense the flow of water around its body.

The jaws suggest that the animal was a predator, biting and holding prey with a row of fangs and drawing food into the mouth with suction.

But the pectoral fin of the Qikiqtania is the most surprising. It has a humerus, just like our upper arm. But Qikiqtania has a very unusual shape.

In early tetrapods such as Tiktaalik, the humeri had a prominent ridge on the underside and a distinctive set of tubercles where the muscles were attached. These bony bumps tell us 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.

The humerus of Qikiqtania is different from others. It lacks characteristic ridges and processes. Instead, the humerus is thin and boomerang-shaped, while the rest of the fin is large and paddle-like. This fin was made for swimming.

While other early tetrapods were playing at the water’s edge, exploring what land had to offer, Qikiqtania was doing something else. Her humerus is truly unlike any known.

My colleagues and I believe that it shows that Qikiqtania has turned back from the water’s edge and evolved to live off-land and in open water again.

Evolution is not a march in one direction

Evolution is not a simple, linear process. While it may seem that early tetrapods inevitably aspired to life on land, Qikiqtania demonstrates the limitations of such a directional perspective.

Evolution did not build a ladder leading to man. It is a complex set of processes that grow together on the intricate tree of life. New species are being formed and they are diversifying. Branches can branch in any number of directions.

This fossil is special for many reasons. It is not only a miracle that this fish was preserved in the breed for hundreds of millions of years before it was discovered by scientists in the Arctic, on Ellesmere Island. It’s not just that she’s amazingly plump, and her complete anatomy was discovered by a stroke of luck on the cusp of a global pandemic.

It also provides, for the first time, a glimpse into the wide diversity and diversity of fish lifestyles as they move from water to land. It helps researchers see more than the stairs and understand this fascinating, intricate tree.

Discoveries depend on the community

Kikiktania was found in Inuit land and belongs to this community. My colleagues and I were only able to carry out this research thanks to the generosity and support of the people of Resolute Bay and Grise Fjord, the hunters and trappers Ivik of Grise Fjord, and the Nunavut Department of Heritage and Culture.

To them, on behalf of our entire research team, “nakurmiik”. Thank you. Paleontological expeditions to their land have really changed our understanding of the history of life on Earth.

COVID-19 has made it impossible for many paleontologists to travel and visit field sites around the world in the past few years. We can’t wait to go back, visit old friends and go looking again.

Who knows what other animals lurk, waiting to be discovered inside blocks of unassuming stone.


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