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Fossil shows fish evolved to walk on land — then went back to the water

MARY LOUISE KELLY, HOST:

You may have come across a meme showing an ancient fish known as a Tiktaalik. It shows illustrations of a green, eel-like, ancient fish.

JUANA SUMMERS, HOST:

Scientists say, around 375 million years ago, that fish crawled from the sea with the physical characteristics to survive on land.

KELLY: A notable link in the evolutionary chain - and versions of the meme basically urge the fish to crawl back into the water to avoid the woes of our modern times.

SUMMERS: But there's new evidence that maybe a version of it did turn right around.

NEIL SHUBIN: It's basically - you had this evolutionary series of fish evolving to walk, but this one said, eh, not going to do that one. I'm going back in.

SUMMERS: That is professor Neil Shubin. He's a paleontologist at the University of Chicago. He first discovered a fossil of Tiktaalik in the Canadian Arctic in 2004, and now he's co-authored a new study on the recent discovery of another related species.

SHUBIN: This new species is a very close cousin of Tiktaalik. We know that by looking at all the features. In fact, it's a very close cousin of both Tiktaalik and creatures with arms and legs and fingers and toes, so-called tetrapods.

KELLY: They call this cousin a Qikiqtania wakei. Using different statistical models, the team was able to conclude that these two fish were related.

SUMMERS: Thomas Stewart is an evolutionary biologist and associate professor at Penn State who also worked on this study. He says the newly discovered fossil has a totally different fin from its relative.

THOMAS STEWART: This animal, despite being closely related to a lot of other animals that are propping themselves up on the ground - whether underwater or perhaps on land - this is an animal that was using its fins for swimming.

SUMMERS: So while one had fins with bones more similar to a human and venturing out onto land, the other was going back to the water, likely because it found advantages for survival in the water again. Qikiqtania is a clear example of just how complicated evolution can be. Professor Thomas Stewart again.

STEWART: We got introduced to the idea of evolution through images like an ape that slowly stands upright and then produces a man walking. Those are some of these classic, iconic teaching tools that people have used to introduce the idea of evolution.

KELLY: But Stewart and Shubin both say this new discovery is an example of how evolution doesn't quite work in a linear way.

SHUBIN: Evolution is much more of a bush - a tree of creatures evolving in many different directions.

SUMMERS: We'll see how the memes evolve from here.

(SOUNDBITE OF MIRAA MAY SONG, "INTERNET TROLLS") Transcript provided by NPR, Copyright NPR.

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Kai McNamee
Ashley Brown is a senior editor for All Things Considered.