Fish Fossil Discovery Researchers report that they've found a key fossil showing a step in the evolutionary transition from fish with fins to four-legged animals that could crawl out onto dry land. Ira Flatow talks to one of the researchers who was in on the find.

Fish Fossil Discovery

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From NPR News in New York, this is TALK OF THE NATION: SCIENCE FRIDAY.

I'm Ira Flatow. When did fish first walk on land? This week, scientists announced the find of a fossil fish in the process of becoming a land animal, representing the historic transition from water to land for animal life on Earth. This hour, we'll talk with one of the scientists who made the discovery. It's more than fossil feet, but is it the missing link?

Plus, a look at the strange world of quantum computing: a world where things can spin to the left and to the right at the same time, switches can be both on and off, and where a cloud of chilled atoms could pack more computing power than the PC on your desk. It's all coming up after this break. Stay with us.

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This is TALK OF THE NATION: SCIENCE FRIDAY. I'm Ira Flatow. A bit later in the hour, the spooky world of quantum computing. But first, a new fossil find about the evolution of life. Back in the mid to late 1800s, several specimens of a fossil bird called Archaeopteryx were found.

It had feathers like modern birds but also characteristics of a reptile. So, it had led some scientists to place it as a transitional animal on the evolutionary tree--with the feathers and the fact that it, you know, it also looked like a regular animal--as a transition from dinosaurs to birds.

Well, now researchers say they've found another fossil representing a key moment in evolution, a time when fish began to grow legs and explore the land beyond the water. Writing this week in the journal Nature, researchers described a fossil dating to some 375 million years ago, a fossil fish, developing limbs and other body structures that make suitable to walk on land as well as swim. And joining me now to talk about this, is one of the researchers who found the fossil, Ted Daeschler, Curator of Vertebrate Biology at the Academy of Natural Sciences in Philadelphia. Welcome to Science Friday.

Dr. EDWARD DAESCHLER (Curator, Vertebrate Biology, Academy of Natural Sciences): Thank you, Ira, a pleasure to talk with you.

FLATOW: Thank you. Is this the scientific equivalent of that Darwin fish logo we see at, on the back of some cars?

Dr. DAESCHLER: Ira, I've been waiting for somebody to point that out, and you're the first one. I, it absolutely is. This is the Darwin fish.

FLATOW: Tell us about--give us a little history about the--how this whole, you know, if we could go back 375 million years, what would we see?

Dr. DAESCHLER: Well, the world was full of fish, but there was nothing walking around on land. Plants had just made the transition to land in the 30 or 40 million years subsequent to the time period that we study. So for the first time in Earth history, there was a productive ecosystem on land, particularly in the flood plains and even wetlands that would have developed along stream systems.

And once the plants made that transition and invertebrate animals, like scorpions, millipedes and spiders--for which we have fossil evidence of also making that transition to the land, the shallow stream systems--that was an ecological opportunity. And so fish began to take advantage of that opportunity and exploit the environments, and swamps, and streams, and ponds in shallow, fresh water systems. And once fish made that transition to shallow water, they were developing features which would eventually allow them to start to move onto land for more longer periods of time.

FLATOW: And so one of those would be the feet.

Dr. DAESCHLER: Well, yes, absolutely. This form that we've just described— Tiktaalik is the scientific name we've given it—it clearly shows features in the fin, for example, that are precursors to the bones and some of the structural precursors to limbs. And it would have used this fin for contact, probably mostly in shallow water...

FLATOW: Mm hmm.

Dr. DAESCHLER: with the substrate, the muddy bottom; maybe climbing around logs, up and over logs; maybe even across mudflats to get to another body of water. Still a fish, no doubt about it, still with some fishy features as well, but developing those structures which would be useful when life on land became possible. And as you mentioned earlier, there's other structural features of this animal, other parts of the body that also are much more like early limbed animals than they are fish.

FLATOW: Such as?

Dr. DAESCHLER: Well, if we look at the skull, for example, although the lower jaw is just like the lower jaws we see in lobed-finned fishes--which is the lineage that leads up to something like the form we've just described--the back of the skull is very modified. It's shortened behind the eye sockets, which is something you see in early tetrapods.

It's also got deep notches in that rear margin of the skull--another feature that you see only in early tetrapods and not in fish. And maybe most dramatically about the skull, it's actually lost a series of bones which connect the skull to the shoulders in most fish—we call it the opercular series. And fish have that bony connection, and tetrapods do not have that bony connection until we found a fish that has lost that bony connection just like early tetrapods have. There's no, the skull is now free from the shoulder girdles.

And the last features to point out are, that although it still has scales covering the body like primitive fish, under those scales is a ribcage where the ribs have widened and overlap each other, suggesting an animal that had a rigid trunk--a trunk that could not compress while the animal moved through very shallow water, where gravity became a force as it may have been partially exposed, or even across land.

So we have features that look back toward fish but look forward toward early tetrapods. It's what we refer to as mosaic evolution, and it's just what we might have predicted in animal along this transition to have had--although we couldn't quite have predicted the combination of features occurring in Tiktaaliks the way we see it.

FLATOW: Would you surmise from looking at the fossil that it also had lungs so it could survive out on the land?

Dr. DAESCHLER: Absolutely. There are nostril openings on the snout of this animal, suggesting that when it was in the water even that it could, the snout would be up and it could take air into its mouth. The shape of the skull, in general, is indicative of an animal that could, what we call, gulp air--in other words, take air in its mouth and squeeze the mouth cavity closed to push air back into lungs. And, in fact, it's kind of counterintuitive, but lungs are a common feature of fishes at the time, especially this group of fishes called lobed-finned fishes.

So even animals that you and I have no trouble calling a fish, that clearly lived in open water--they also had the, had lungs as well as gills, which is a handy thing to have if you're going through low-oxygenated water and you do want get enough oxygen to run your metabolism. If you can use a system based on lungs and a system, and/or a system based on gills, you've got two tools there.

FLATOW: Mm. There are other samples of animals from around that time. What does this one have that the others don't?

Dr. DAESCHLER: Well, you're exactly right. We have known about some possible precursors for early tetrapods among lobed-fin fish. One is called Panderichthys, and that always sat as the example of the fish that was closest to tetrapods, although we don't see a lot of the tetrapod features. I use the word tetrapod to--as what limbed animals are—we don't see a lot of tetrapod features in something like Panderichthys. And then we do have the earliest tetrapods which show up at the end of the Devonian period, things like Acanthostega.

But in-between those forms, we've known only sort of isolated bones, scrappy material, nothing that could really give us an overall picture of the animal and show us how different features and different parts of the skeleton were developing in concert or in a mosaic fashion, as I mentioned earlier. And this form, Tiktaalik, is so complete.

We have really remarkably preserved fossils, given its age, and so well-preserved that we're able to study details of many parts of the body in one species here--and see what is evolving and what came first--and come up with ideas about what pressures, what sort of natural selection pressures may have driven the evolution of one suite of features or another.

FLATOW: Would it be fair to say that this does fill a crucial gap that's been missing?

Dr. DAESCHLER: There has been a gap in information, right through this fish-to tetrapod-transition. It's been a very firm hypothesis through the years, that these lobed-fin fish gave rise to the early tetrapods. Going back more than a hundred years, people have seen the similarities, but we were never able to sort of fill that gap with a fossil that showed us how these things were acquired and in the combination that they were acquired. So in deed, it does fill a gap.

FLATOW: Where was it discovered?

Mr. DAESCHLER: Up on Ellesmere Island in the Canadian Arctic. I've worked here in Pennsylvania where we have late Devonian age rock. Started my work with a man named Dr. Neil Shubin who I've continued to collaborate with through the years, and Dr. Shubin and I were looking for a place where we might find late Devonian rock that's formed in shallow streams systems.

And using geological work--and it just shows how science works, we sort of built our work on the work that geologists had done before us, we would never had known to go there if the geologists hadn't done their mapping up in the Canadian Arctic--but we found that the rocks there met the criteria that we hoped that might preserve both this transition as well as all the other fish that were living at the time--a lot of interesting evolutionary action back in the late Devonian period. It was a real consequential time when some groups were growing extinct and other groups, many of which we know today as the dominant vertebrate groups on earth, were just getting started--things like sharks and ray-finned fishes, and early tetrapods which is what, of course we've been focusing on.

FLATOW: Mm hmm.

Mr. DAESCHLER: But, so Dr. Shubin and I sort of took a shot in the dark and we organized an expedition. We enlisted, among others, Dr. Ferris Jenkins from Harvard who had had a lot of Arctic paleontological experience and we organized ourselves, and equipment, and logistics to get all the way up to Ellesmere Island--which is a long way up in the Nunavut Territory which is that part of Canada that was separated from Northwest Territories in 1999 to be an Inuit homeland. And it's been a fantastic place to work, and although it's a little bit harsh, weather wise, as long as we're prepared…

FLATOW: Yeah, yeah.

Mr. DAESCHLER: …we are quite efficient at getting our nose up to the rock and our feet on the ground and spending the time it takes to find these fossil sights.

FLATOW: Will this fossil be visible to the public on display anyplace, for us to look at it?

Mr. DAESCHLER: Yes, here at the Academy of Natural Sciences in Philadelphia, we're going to put several of the specimens out on exhibit on April 12. And, I'm sure that there will be--we actually have a Web site at University of Chicago,, where people can go and learn more about it and see a lot of images and some images of the field work. So, we're trying to make sure that the outreach is there so that anybody who's interested can learn more about this animal.

FLATOW: Did you find--I only have a few seconds left--did you find more than one fossil, or was this basically one single fossil?

Mr. DAESCHLER: No, it's, we have several individuals represented by skulls, shoulders, and fins--but then a total of at least 10 individuals, mostly represented by isolated bones; things like lower jaws that preserve really well. So we have a nice sample of well preserved material to draw from. So we really have gotten to know this animal well. Although I must say, we have additional work to do on parts of the skeleton that we haven't studied in detail. And by the way, we're going to go back. We haven't found the hind fins so we hope we find some stuff about those, what we call pelvic fins. So, look for more.

FLATOW: Good luck. All right and we'll have you back. Thank you very much for taking time to be with us.

Mr. DAESCHLER: Thank you Ira, my pleasure.

FLATOW: Ted Daeschler, curator of vertebrate biology at the Academy of Natural Sciences in Philadelphia.

Short break. Come back, we're going to talk about quantum computing and why the universe is a giant quantum computer. Stay with us.

I'm Ira Flatow; this is TALK OF THE NATION SCIENCE FRIDAY from NPR News.

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