Fossil from the Arctic shows evolutionary return to open water
One of the great mysteries in evolution is the question of when which animal took the path from the water to land. Two years ago, researchers at the University of Chicago accidentally found a fossil from the Arctic north of Canada that may have been one of the first animals to go this way. Now, researchers from the same university have discovered a fossil of a close ancestor that preferred to stay in the water rather than go ashore.
Go ashore or rather stay in the water? A representative of the lobe-finned fish or Elpistostegalia faced this question 375 million years ago. The animal, named Tiktaalik roseae by its discoverers, decided to step on land and was one of the first land vertebrates. That’s what Professor Neil Shubin and his colleague Ted Daeschler found two years ago after examining fossils they had found more than 15 years earlier during excavations in the southwest of the Canadian Arctic island of Ellesmere.
Now the researchers could put another piece in the puzzle about the evolution to terrestrial vertebrates (and ultimately to us). Just a little away from the Tiktaalik site lay another fossil, about 15 million years older than Tiktaalik, but which had been a close relative and had preferred not to go ashore but to stay in the water. This although its fins had already ceased to be fish-like. The animal was named Qikiqtania wakei, after the late evolutionary biologist David Wake. That’s what the authors write in their study, which has been published recently in the journal Nature.
Neil Shubin’s two postdoctoral assistants, Dr. Tom Stewart and Dr. Justin Lemberg, had made the surprising find in a rock block using a CT scanner in 2020. But because the university had the labs closed due to the pandemic, more detailed investigations could not resume until later in the year. “We first thought it was a young Tiktaalik because everything was smaller and didn’t appear to be fully developed,” Neil Shubin explained in a university news release. “But the humerus is smooth and boomerang-shaped, and it doesn’t have the elements that would support it pushing up on land. It’s remarkably different and suggests something new.”
The results of the research show that Qikiqtania had preferred to swim, but in a manner that did not conform to the usual style of lobe-finned fish, which had progressed slowly toward shore. “This unexpected morphological and functional diversity represents a previously hidden ecological expansion, a secondary return to open water, near the origin of limbed vertebrates,” the authors conclude in the paper.
According to the team, Qikiqtania was only about 75 centimeters tall, while its relative Tiktaalik was about 2.7 meters long. Both fossils were found in the southwest of Ellesmere Island in Nunavut. The name Qikiqtania also refers accordingly to the place of discovery, which is called Qikiqtaaluk in Inuktiut. The name Tiktaalik, on the other hand, describes a burbot, a fresh or brackish water fish that is eaten by the Inuit in Canada. The finding of Qikiqtania shows that the group of animals that gave rise to the land vertebrates was much more diverse than previously thought and that many of them are found in today’s subarctic and arctic regions. During the Middle and Late Devonian, however, these sites were much farther south, in warmer climates. Nevertheless, the story of how terrestrial vertebrates evolved is probably deep in the Arctic soil.
Dr. Michael Wenger, PolarJournal
Link to the study: Stewart et al. (2022) Nature July 20, A new elpistostegalian from the Late Devonian of the Canadian Arctic; https://doi.org/10.1038/s41586-022-04990-w
