New fossil shows four-legged fishapod that returned to the water while Tiktaalik ventured onto land
Members of the Shubin lab describe a new fossil that is closely related to other animals that made the transition to land, but with features more suited for swimming and life in the water.
Our team has discovered a new fossil species that closely resembles Tiktaalik roseae, the iconic, four-legged “fishapod” that first made the transition from water to land 375 million years ago. The new species, Qikiqtania wakei, was small—just 30 inches long—compared to Tiktaalik, which could grow up to nine feet. The new fossil includes partial upper and lower jaws, portions of the neck, and scales.
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Reconstruction by: Alex Boersma
Most importantly, it also features a complete pectoral fin with a distinct humerus (upper arm bone) that lacks the ridges that would indicate where muscles and joints would be on a limb geared toward walking on land. Instead, Qikiqtania’s upper arm was smooth and curved, more suited for a life paddling underwater.
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Neil Shubin, PhD, the Robert R. Bensley Distinguished Service Professor of Organismal Biology and Anatomy at the University of Chicago, discovered both the Qikiqtania and Tiktaalik fossils days apart in 2004, at a site on southern Ellesmere Island, Nunavut, in Northern Arctic Canada. The name Qikiatania comes from the Inuktitut word Qikiqtaaluk or Qikiqtani, the traditional name for the region where the fossil site occurs. The species designation wakei is in memory of the late David Wake, an eminent evolutionary biologist from the University of California at Berkeley.
Tom Stewart, PhD, and Justin Lemberg, PhD, who were then postdoctoral scholars at UChicago, CT scanned a rock containing the fossil pectoral fin and discovered its distinctive shape. The team’s analysis of where it sits on the tree of life places it, like Tiktaalik, adjacent to the earliest creatures known to have finger and toes. Even though Qikiqtania’s distinct pectoral fin was more suited for swimming, its curved paddle shape was a distinct adaptation, different from the jointed, muscular legs or fan-shaped fins we see in tetrapods and fish today.
Glimpses into vertebrate history
Qikiqtania is slightly older than Tiktaalik, but not by much. Both were discoverd in Late Devonian deposists. However, Qikiqtania was 70 meters lower in the formation. The team’s analysis of where it sits on the tree of life places it, like Tiktaalik, adjacent to the earliest creatures known to have finger-like digits.
“Tiktaalik is often treated as a transitional animal because it’s easy to see the stepwise pattern of changes from life in the water to life on land. But we know that in evolution things aren’t always so simple,” said Stewart, who is now an Assitant Professor at Penn State University. “We don’t often get glimpses into this part of vertebrate history. Now we’re starting to uncover that diversity and to get a sense of the ecology and unique adaptations of these animals. It’s more than simple transformation with just a limited number of species.”
A prehistoric pandemic project
Shubin and his field partner, Ted Daeschler, PhD, from the Academy of Natural Sciences of Drexel University, collected the specimen from a few promising rocks that showed a partial jaw and distinctive white scales on the surface. But they sat in storage, mostly unexamined, while the team focused on preparing Tiktaalik.
Sixteen years later, the discovery of Qikiqtania became another pandemic story. Postdoctoral researchers Justin Lemberg, PhD, and Tom Stewart, PhD, CT scanned one of the larger rocks in March 2020 and realized that it contained a pectoral fin. Unfortunately, the rock was too large 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 of the material as we could before the lockdown, and the very last piece we scanned was a large, unassuming block with only a few flecks of scales visible from the surface,” said 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 came into view. We knew we could collect a better scan of the block if we had the time, but that was March 13th, 2020, and the University shut down all non-essential operations the following week.”
In the summer of 2020 when campus facilities reopened, they contacted Mark Webster, PhD, Associate Professor of Geophysical Sciences, who had access to a saw that could trim pieces off the specimen so that a CT scanner could get closer and produce a better image. Lemberg and Stewart carefully marked the boundaries on the block and arranged an exchange outside their lab in Culver Hall. The resulting images revealed a nearly complete pectoral fin, including the distinctive humerus bone.
“That’s what blew our minds,” Shubin said. “This was by no means a fascinating block at first, but we realized during the COVID lockdown when we couldn’t get in the lab that the original scan wasn’t good enough and we needed to trim the block. And when we did, look at what happened. It gave us something exciting to work on during the pandemic. It’s a fabulous story.”
This research was supported by the Brinson Foundation, the Academy of Natural Sciences of Drexel University, the University of Chicago Biological Sciences Division, the Polar Continental Shelf Project of Environment Canada, the Nunavut Department of Culture and Heritage, the Hamlet and Hunter and Trappers of Grise Fiord, and the National Science Foundation.
Educational Resources and Links
The New York Times “These Fins were made for walking… and then swimming”
The Conversation “Meet Qikiqtania, a fossil fish with the good sense to stay in the water while others ventured onto land“
TechNewsBoy “New Fossil Shows Four-Legged Fishapod That Returned To The Water While Tiktaalik Ventured Onto Land: Researchers Discover A New Fossil That Is Closely Related To Other Animals That Made The Transition To Land, But With Features More Suited For Swimming And Life In The Water“
EurekAlert! “New fossil shows four-legged fishapod that returned to the water while Tiktaalik ventured onto land“
TVN “New fossil shows four-legged fishapod that returned to the water while Tiktaalik ventured onto land“