About 365 million years ago, a group of fish left the water to live on land.
These animals were the first tetrapods, a lineage that would radiate to include many thousands of species, including amphibians, birds, lizards, and mammals. Human beings are the descendants of these early tetrapods, and we share the legacy of their water-land transition.
What if, instead of venturing to the shores, they had turned back? What if these animals, just about to leave the water, had retreated to live again in more open waters?
A new fossil suggests that a fish, in fact, did just that. Unlike other closely related animals, which used their fins to support their bodies at the bottom of the water and perhaps occasionally ventured onto dry land, this newly discovered creature had fins designed for swimming.
In March 2020, I was at the University of Chicago and a member of biologist Neil Shubin’s lab. I was working 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 jaws, about 2 inches long (5 cm) and with sharp teeth. There were also patches of white scales with a bumpy texture. The anatomy gave us subtle clues that the fossil was an early tetrapod. But we wanted to see inside the rock.
So we used a technology called computed tomography, which shoots x-rays through the sample, to look for anything that might be hidden inside, out of sight.
On March 13, we scanned an unassuming piece of rock that had a few scales on top and found it had a full fin buried inside. Our jaws dropped. A few days later, the lab and campus closed and COVID-19 put us in lockdown.
The fin unveiled
A fin like this is extremely valuable. This can give scientists clues to the evolution of early tetrapods 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 was swimming or walking.
Although this first scan of the fin is 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 geophysical science department helped us carve the block with a stone saw.
This made the block thinner, less rock, allowing for better sweeping and a closer view of the fin.
When the dust cleared 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 to be one of the closest known relatives of limb 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 Where Qikiqtanithe traditional name of the region where the fossil was found.
When this fish was alive several hundred million years ago, it 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 speaks volumes about a critical period in the history of our lineage. Its scales unambiguously tell researchers that it lived underwater. They show sensory channels that would have allowed the animal to detect the flow of water around its body.
Its jaws tell us that it fed like a predator, biting and latching onto its prey with a series of fangs and sucking food into its mouth.
But he is Qikiqtaniapectoral fin which is the most surprising. It has a humerus bone, just like our arm. But Qikiqtania‘s a very particular form.
The first tetrapods, like Tiktaalik, have humeri that possess a prominent ridge on the underside and a characteristic set of bumps, where the muscles attach. These bony bumps tell us that early tetrapods lived at the bottom of lakes and streams, using their fins or arms for support, first on the ground underwater and later on land.
QikiqtaniaThe humerus is different. It lacks those trademark ridges and processes. Instead, its humerus is thin and boomerang-shaped, and the rest of the fin is wide and paddle-like. This fin was designed for swimming.
As other early tetrapods played by the water’s edge, learning what the land had to offer, Qikiqtania was doing something different. His humerus is unlike any other known.
My colleagues and I think this shows that Qikiqtania turned away from the water’s edge and evolved to live, once again, above ground and in open water.
Evolution is not a march in one direction
Evolution is not a simple, linear process. Although it may seem that the first tetrapods inevitably tended towards terrestrial life, Qikiqtania shows exactly the limits of such a directional perspective.
Evolution did not build a ladder to humans. It is a complex set of processes that together grow the tangled tree of life. New species are forming and diversifying. Branches can branch off in any number of directions.
Above: Neil Shubin, who found the fossil, pointing across the valley to the site where Qikiqtania was discovered on Ellesmere Island.
This fossil is special for many reasons. It’s not just miraculous that this fish was preserved in rock for hundreds of millions of years before it was discovered by scientists in the Arctic on Ellesmere Island. It’s not just that he’s remarkably complete, with his full anatomy accidentally revealed on the cusp of a global pandemic.
It also provides, for the first time, insight into the greater diversity and range of fish lifestyles during the water-land transition. It helps researchers see more than a scale and understand this fascinating, tangled tree.
Discoveries depend on the community
Qikiqtania was found on Inuit land and belongs to that community. My colleagues and I were only able to conduct this research through the generosity and support of people from the hamlets of Resolute Bay and Grise Fiord, the Iviq Hunters and Trappers of Grise Fiord, and the Nunavut Department of Heritage and Culture .
To them, on behalf of our entire research team, “nakurmiik”. Thanks. The paleontological expeditions to their lands have truly changed our understanding of 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 can’t wait to come back, visit old friends and search again.
Who knows what other animals lurk, waiting to be discovered inside unassuming blocks of stone.
Thomas Stewart, Assistant Professor of Biology, Penn State
This article is republished from The Conversation under a Creative Commons license. Read the original article.