Our ancient ancestors, as with all land-based life on Earth, evolved in our planet’s primordial seas before taking their first steps onto land. For vertebrates like us, the animal commonly associated with this evolutionary stride is the 375 million-year-old Tiktaalik roseae.
For its leap of faith into the Darwinian bible, Tiktaalik has received some tongue-in-cheek flak from internet memesters who blame the amphibious trailblazer for all life’s modern problems.
Memes circulated in the last couple of years bemoan the prehistoric critter’s adventurousness and articulate the not insincere desire to time-travel and coax Tiktaalik back into the water.
Others wonder if this would only have led to a dystopia filled with war, rent, plague and unfair bosses emerging under the ocean waves.
Funnily enough, minus the time-travelling millennials shooing the fishapods (early fish which developed limbs for walking) back into the water, the meme might actually parallel reality.
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Research published in Nature on a new fossil shows a fishapod which appears to have joined Tiktaalik on land – before deciding to return to the sea, sparing its ancestors the pain of 21st century life.
Co-author of the new study and University of Chicago evolutionary biologist Neil Shubin was also a leader in the team which co-discovered Tiktaalik back in 2004.
The new fossil belonged to a similar creature called Qikiqtania wakei which would have been just a little over a metre in length – small compared to Tiktaalik which could grow to nearly three metres.
Qikiqtania’s fossils were found just days before Tiktaalik was discovered. Qikiqtania is named after the Inuktitut word Qikiqtaaluk or Qikiqtani, traditional names for the region where the fossil was found. The species designation “wakei” is in memory of the late David Wake, an eminent evolutionary biologist from the University of California at Berkeley, US.
Though Qikiqtania shared many of the same features as its exploratory cousin, the newly discovered animal’s body is more suited to life in water. Among the fossils are partial upper and lower jaws, portions of the neck and scales, and, most importantly, a complete pectoral fin complete with a humerus bone lacking the muscle ridges that would indicate a limb built for walking on land.
Qikiqtania’s upper arm was smooth and curved, suggesting it spent its life paddling underwater. The unique arm bones imply that it returned to the water after its ancestors began to use their appendages for walking.
“At first we thought it could be a juvenile Tiktaalik, because it was smaller and maybe some of those processes hadn’t developed yet,” Shubin said. “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.”
Thrust into Tiktaalik’s shadow, the Qikiqtania fossils were placed in storage and largely forgotten for 15 years.
It was only in March 2020 that a CT scan of one of the rocks revealed a pectoral fin. Too deep in the rock to get a decent image and abandoned again when lockdowns forced labs to close, the fin was left high and dry until later that year.
“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,” explains co-author Justin Lemberg.
“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 in March 2020, and the University shut down all non-essential operations the following week,” Lemberg adds.
When facilities reopened and scans could be completed after trimming the rock around the specimen, the near-complete pectoral fin and upper limb came into view.
“That’s what blew our minds,” Shubin says. “This was by no means a fascinating block at first, but we realised 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.”
Slightly older than Tiktaalik, Qikiqtania shares a part of the evolutionary tree of life adjacent to the earliest vertebrates with finger-like digits.
The discovery and analysis highlight that animals don’t evolve in linear paths. It’s not as simple as drawing a straight line between modern organisms and some earlier forms. Qikiqtania shows that some creatures will stray onto different paths – some of which don’t work out.
“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,” says lead author Thomas Stewart. “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.”
So, to all the internet detractors of Tiktaalik, evolution tried the “going back in the water thing” as well. And it’s thanks to those early fishapods that you can give the poor, wet pioneers the middle finger in the first place!
Originally published by Cosmos as While our ancestors went from sea to land, this 400 million-year old fishapod high-tailed it back into the water
Evrim Yazgin has a Bachelor of Science majoring in mathematical physics and a Master of Science in physics, both from the University of Melbourne.
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