Meet Qikiqtania, a fossil fish that stayed 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 included many thousands of species, including amphibians, birds, lizards, and mammals. Humans are descendants of these early tetrapods, and we share the legacy of their transition from water to land.

But what if, instead of venturing to the coast, they turned around? What if these animals had retreated just before leaving the water to live in more open waters again?

A new fossil suggests a fish actually did just that. Unlike other closely related animals, which propped their bodies on the bottom of the water with their flippers and might occasionally venture onto land, this newly discovered creature had flippers built for swimming.

In March 2020, I was at the University of Chicago and a member of biologist Neil Shubin’s lab. I worked with Justin Lemberg, another researcher in our group, to process a fossil collected during a 2004 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 sharp teeth. There were also patches of white scales of uneven texture. The anatomy gave us subtle clues that the fossil was an early tetrapod. But we wanted to look inside the rock.

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So we used a technology called CT scanning, which shoots X-rays through the sample to look for anything that might be hiding inside it out of view. On March 13, we scanned a nondescript piece of rock that had a few scales on top and found that an entire fin was buried within. Our jaws dropped. A few days later the lab and campus were closed and COVID-19 sent us into lockdown.

The fin revealed

Such a fin is extremely valuable. It may give scientists clues as to how early tetrapods evolved and how they lived hundreds of millions of years ago. For example, we can use the shape of certain bones in the skeleton to make predictions about whether an animal has swum or walked.

While this first 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 geophysics department helped us cut the block down with a stone saw. This made the block more fin, less rock, allowing for a better scan and closer view of the fin.

When the dust settled and we finished analyzing the data on the jaws, scales, and fins, we realized that this animal was a new species. Not only that, it turns out that this is one of the closest known relatives of limbed vertebrates – those creatures with fingers and toes.

We named it Qikiqtania wakei. Its 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 lived many hundreds of millions of years ago, this was a warm environment with rivers and streams. Its species name honors the late David Wake, a scientist and mentor who inspired so many of us in the field of evolutionary and developmental biology.

Skeletons tell how an animal lived

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

But it is Qikiqtania‘s pectoral fin, the most surprising. It has an upper arm bone, just like our upper arm. but Qikiqtaniahas a very special shape.

Early tetrapods, like tiktalik, have humeri that have a prominent crest on the underside and a characteristic row of bumps where muscles attach. 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 the bottom underwater and later on land.

Qikiqtania‘s humerus is different. It lacks these characteristic ridges and processes. Instead, its humerus is thin and boomerang-shaped, and the rest of the fin is large and paddle-like. This fin was built for swimming.

While other early tetrapods played by the water and learned what the land had to offer, Qikiqtania did something different. His humerus is truly unlike any other known one. My colleagues and I think that shows that Qikiqtania had retired from the water and evolved to live above the bottom and in open water again.

Evolution is not a march in one direction

Evolution is not a simple, linear process. Although it may appear that early tetrapods inevitably tended to live on land, Qikiqtania shows exactly the limits of such a directional perspective. Evolution has not built a ladder to man. It is a complex series of processes that together grow the intricate tree of life. New species form and they diversify. Branches can go in any number of directions.

This fossil is special for so many reasons. It’s not just a miracle that this fish was preserved in rock for hundreds of millions of years before being discovered by arctic scientists on Ellesmere Island. Not only is it remarkably complete, with its complete anatomy revealed by serendipitous coincidence on the cusp of a global pandemic. It also offers, for the first time, a glimpse into the broader diversity and range of life styles of fish as they make the transition from water to land. It helps researchers see more than one ladder and understand this fascinating, tangled tree.

Discoveries depend on the community

Qikiqtania was found on Inuit land and belongs to this community. My colleagues and I have only been able to undertake this research because of 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 you, on behalf of our entire research team, “nakurmiik”. Many Thanks. Paleontological expeditions to their land have truly changed our understanding of the history of life on Earth.

COVID-19 has kept many paleontologists from traveling and visiting field sites around the world in recent years. We look forward to returning, visiting old friends and searching again. Who knows what other animals are hidden in nondescript blocks of stone, waiting to be discovered.

This article was republished by The Conversation under a Creative Commons license. Read the original article.