They find the fossil of a four-legged fish that returned to the water

July 20 () –

A new study from the laboratory of Neil Shubin of the University of Chicago (United States), have found a fossil species that closely resembles the Tiktaalik, the iconic four-legged fish that first made the transition from water to land 375 million years agobut that it has characteristics that made it more suitable for life in the water than its adventurous cousin, according to what is published in the magazine ‘Nature’.

One of the close relatives of Tiktaalik chose to return to living in open water rather than venture onto land. The new study from the lab of Dr Neil Shubin, who co-discovered Tiktaalik in 2004, describes a fossil species that closely resembles Tiktaalik, but has characteristics that make it more suited to life in water than its adventurous cousin.

Qikiqtania wakei was small — just 75 centimeters long — compared to Tiktaalik, which could grow to nearly 3 meters. The new fossil includes partial upper and lower jaws, neck parts and scales.

Most importantly, the researchers say, it also features a complete pectoral fin with a distinct humerus bone that lacks the ridges that would indicate where muscles and joints would be in a land-oriented limb.

Instead, Qikiqtania’s upper arm was smooth and curved, more suited to a life of paddling underwater. The uniqueness of the arm bones suggests that it returned to rowing in the water after its ancestors began using its appendages to walk.

“At first we thought it might be a juvenile Tiktaalik, because it was smaller and maybe some of those processes hadn’t developed yet. Shubin explains. But the humerus is smooth and boomerang-shaped, and it doesn’t have the elements that would allow it to push up on land. It’s remarkably different and suggests something new,” he says.

Shubin, who is a professor of biology and organismal anatomy at the University of Chicago, found the fossil days before Tiktaalik was discovered, at a site about a mile east of South Ellesmere Island, in Nunavut Territory, in the northern Canadian Arctic.

The name Qikiatania comes from the Inuktitut word Qikiqtaaluk or Qikiqtani, the traditional name of the region where the fossil site is located. The species designation wakei is in memory of the late David Wake, an eminent evolutionary biologist at the University of California at Berkeley.

Shubin and his field partner, Dr. Ted Daeschler of Drexel University’s Academy of Natural Sciences, collected the specimens from a quarry after spotting a few promising-looking rocks with characteristic white flakes on the surface. But they were left in storage, mostly unexamined, while the team focused on preparing Tiktaalik.

Fifteen years later, the discovery of Qikiqtania became another pandemic story. Postdoctoral researchers Justin Lemberg and Tom Stewart scanned one of the largest rock specimens in March 2020 and realized it contained a pectoral fin. Unfortunately, it was too deep within the rock to get a high-resolution image, and they couldn’t do much more with it once the pandemic forced labs to close.

“We were trying to collect as much CT data as we could before lockdown, and the last piece we scanned was a large, inconspicuous block with only a few flakes visible on the surfacerecalls Lemberg, who is now doing cultural resource management fieldwork in Southern California.

“We could hardly believe it when the first grainy images of a pectoral fin surfaced,” he adds. “We knew we could pick up a better scan of the block if we had time, but that was on March 13, 2020, and the University shut down all operations.” non-essential the following week.

In the summer of 2020, when campus facilities reopened, they contacted Dr. Mark Webster, Associate Professor of Geophysical Sciences, who had access to a saw that could cut out pieces of the specimen so a CT scanner could get closer. and produce a better image.

Stewart and Lemberg carefully marked the block boundaries and arranged an exchange outside their Culver Hall lab. The resulting images revealed a nearly complete pectoral fin and upper limb, including the characteristic humerus bone.

“That’s what blew our minds,” recalls Shubin. “It wasn’t a fascinating block at first, but we realized during the COVID lockdown, when we couldn’t get into the lab, that the original scanner wasn’t what it was.” good enough and that we had to trim the block. And when we did, look what happened. It gave us something exciting to work on during the pandemic. It’s a fabulous story“, he stresses.

The Qikiqtania is slightly older than Tiktaalik, but not by much. The team’s analysis of its position in the tree of life places it, like Tiktaalik, alongside the earliest known creatures with fingers. But while the Qikiqtania’s distinctive pectoral fin was more suited to swimming, it wasn’t entirely fish-like, either. Its curved paddle shape was a different adaptation to the muscular, jointed legs or fan-shaped fins we see in tetrapods and fish today.

People tend to think that animals evolved in a straight line connecting their prehistoric forms with some living creature today, but the Qikiqtania shows that some animals followed a different path that ultimately didn’t work out. Perhaps it’s a lesson for those who wish the Tiktaalik had stayed in the water with him, they add.

“The Tiktaalik is often treated as a transitional animal because it is easy to see the stepwise pattern of changes from life in the water to life on land. But we know that in evolution things are not always so simple.adds Stewart, who will join the faculty at Penn State University this summer.

“We don’t often get a glimpse of this part of vertebrate history. Now we’re starting to discover that diversity and get a sense of the unique ecology and adaptations of these animals. It’s more than just a transformation with a limited number of species “, he assures.