Meet Qikiqtania, a fossil fish with the good sense to stay in the water while others ventured onto land

About 365 million years ago, a group of fish left the water to live on land. These animals were early tetrapods, a lineage that would encompass many thousands of species, including amphibians, birds, lizards and mammals. Humans are descendants of those early tetrapods, and we share the legacy of their transition from water to land.

But what if, instead of venturing to shore, they had returned? What if these animals, just about to leave the water, had withdrawn to live in more open waters again?

A new fossil suggests that one fish, in fact, did just that. Unlike other closely related animals, which used their fins to prop up their bodies on the bottom of the water and might occasionally venture onto land, this newly discovered creature had fins built for swimming.

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

From the surface of the rock in which it was embedded, we could see fragments of the jaws, about 5 cm long and with pointed teeth. There were also patches of white scales with a bumpy texture. The anatomy gave us subtle hints that the fossil was an early tetrapod. But we wanted to look into the rock.

So we used a technology called CT scanning, which shoots X-rays through the sample, to look for something that might be hidden inside, out of sight. On March 13, we scanned a modest piece of rock with a few scales on it and found that it contained a complete fin buried within it. Our mouth fell open. A few days later, the lab and campus closed, and COVID-19 sent us into lockdown.

The fin revealed

Such a fin is extremely expensive. It could give scientists clues about how early tetrapods evolved and how they lived hundreds of millions of years ago. For example, based on the shape of certain bones in the skeleton, we can predict whether an animal swam or walked.

While that initial scan of the fin was promising, we needed to see the skeleton in high resolution. As soon as we were allowed back on campus, a professor from the university’s department of geophysical sciences helped us cut the block with a rock saw. This made the block more fin, less rock, allowing for a better scan and a better view of the fin.

When the dust settled and we finished analyzing data on the jaws, scales and fin, we realized that this animal was a new species. Not only that, it turns out that this is one of the most well-known relatives of vertebrates with limbs — those creatures with fingers and toes.

We called it Qikiqtania wakei. The genus name, pronounced “kick-kiq-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, this was a warm environment with rivers and streams. The species name honors the late David Wakea scientist and mentor who inspired so many of us in the fields of evolutionary and developmental biology.

An animation of Qikiqtania’s pectoral fin showing how it was preserved in the rock. The scales are shown in yellow, fin rays in blue and the endoskeleton in grey. Credit: Tom Stewart

Skeletons tell how an animal lived

Qikiqtania reveals much about a critical period in the history of our lineage. Its scales unequivocally tell researchers that it lived underwater. They show sensory channels that would have enabled the animal to detect the flow of water around its body. Its jaws tell us it was foraging like a predator, biting and holding prey with a series of fangs and drawing food into its mouth by sucking.

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

Early tetrapods, such as Tiktaalik, have humeri with a prominent rim on the underside and a characteristic series of bumps, where muscles attach. These bony humps tell us that early tetrapods lived on the bottom of lakes and streams and used their fins or arms to prop themselves up, first on the ground underwater and later on land.

The humerus of Qikiqtania is different. It lacks those distinctive ridges and processes. Instead, its humerus is thin and boomerang-shaped, and the rest of the fin is large and paddle-like. This fin is made for swimming.

While other early tetrapods played on the waterfront and learned what the land had to offer, Qikiqtania did something different. His humerus is really unlike any other known. My colleagues and I think it shows that Qikiqtania had withdrawn from the waterfront and evolved to live off the ground and in open water again.

An animation of the full skeleton of Qikiqtania. Credit: Tom Stewart

Evolution is not a march in one direction

Evolution is not a simple, linear process. While it may seem that early tetrapods inevitably gravitated toward life on land, Qikiqtania shows exactly the limitations of such a focused perspective. Evolution has not built a ladder to humans. It is a complex series of processes that together grow the tangled tree of life. New species emerge and they diversify. Branches can go in all directions.

This fossil is special for so many reasons. Not only is it miraculous that this fish was kept in the rocks for hundreds of millions of years before being discovered by scientists in the Arctic, at Ellesmere Island. It’s not just that it’s remarkably complete, with its entire anatomy revealed by serendipity on the eve of a global pandemic. It also offers, for the first time, a glimpse of the wider diversity and range of fish lifestyles as they transition from water to land. It helps researchers see more than a ladder and understand that fascinating, tangled tree.

Discoveries depend on the community

Qikiqtania was found on Inuit land and belongs to that community. My colleagues and I were able to conduct this research only thanks to the generosity and support of individuals in the hamlets of Resolute Bay and Grise Fiord, the Iviq Hunters and Trappers of Grise Fiord, and the Department of Heritage and Culture, Nunavut. To them, on behalf of our entire research team, “nakurmiik.” Thank you. Paleontological expeditions to their lands have really changed the way we understand the history of life on Earth.

COVID-19 has prevented many paleontologists from traveling and visiting field sites around the world in recent years. We are eager to return, visit with old friends and search again. Who knows what other animals are hidden waiting to be discovered in blocks of modest stone.

This article was republished from The conversation under a Creative Commons license. Read the original article.