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THE NEWSHOUR WITH JIM LEHRER FOSSIL FIND MISSING LINK BETW LYRICS

[00:00] For fun, scientists are calling it a fishopod -- part fish,
[00:11] part petropod, or four-legged animal. In all seriousness,
[00:15]it's being seen as a crucial missing link in the evolutionary
[00:19]chain between life in the water and on land.
[00:22]The fossils date from some 375 million years ago,
[00:26]and show a creature given the name Tiktaalik.
[00:29]As shown in this model, it ranged from four to nine feet,
[00:32] had fins and scales, but also a neck, ribs
[00:36]and rudimentary limbs. The fossils were found on Ellesmere
[00:39]Island in the Canadian Arctic, and described in the journal
[00:42]"Nature" today. Ted Daeschler, a paleontologist at the Academy
[00:46] of Natural Sciences in Philadelphia, was one of the two lead
[00:50]researches, and he joins us now. Welcome to you.
[00:53] Thank you, Jeff.
[00:54] I saw this described as a transitional creature.
[00:57]Help us understand, would it have been both
[01:00]a land and sea animal?
[01:02] This is still a fish. And so many of its features tie it
[01:06]back to the way we expect fish to behave. It probably lived
[01:10]primarily in the water, probably in very shallow water.
[01:14]We find it in rocks which were deposited in stream systems.
[01:18]And so we're making the hypothesis that this animal was
[01:21]specialized for living in shallow stream systems, perhaps
[01:25]swampy habitats, perhaps even to some of the ponds.
[01:29]And maybe occasionally, using its very specialized fins,
[01:33]for moving up overland. And that's what is particularly
[01:36]important here. The animal is developing features which will
[01:40]eventually allow animals to exploit land.
[01:44]Moving to land
[01:44] All right. You brought a skull along, I gather.
[01:46]You can show us some of those features that part fish, and
[01:50] that perhaps suggest that it could have moved on to land.
[01:53] Absolutely. This is the skull of Tiktaalik. Now, we have
[01:58]several individuals -- this is one of the more well preserved
[02:02]specimens. You see its broadly triangular shape. And it's
[02:06]rather flattened, with eye sockets high on the head.
[02:10]When we look closely at the features of this skull,
[02:13]especially at the lower jaw and the snout, we see that
[02:18]they are very fish-like. In fact, we actually originally found
[02:22]pieces of lower jaw and really couldn't recognize them
[02:25]as anything other than some of the lobe-fin fish that are
[02:29]related to this thing.
[02:30]But it's when we saw some of the other features of the skull,
[02:33]particularly the short area behind the orbits here, as well
[02:37] as these large notches in the back of the skull, that we were
[02:41] startled by the similarity to the first limbed animals, which
[02:45]had skull design just like this.
[02:48]Now, the entire specimen also includes the body, which occurs
[02:52]behind the skull. And in the body, there is also a number of
[02:56]features which suggest tetropod. The fin itself, although
[03:01]it may have looked like a fish fin on the outside, if you could
[03:03]look at the internal skeleton, you would see bony structures
[03:07]reminiscent of a tetropod limb, including a wrist joint and bones
[03:13]beyond the wrist joint which were giving that fin power and dexterity.
[03:17]And again, we think that the animal used its fin for contacting
[03:21]the substrate and moving around.
[03:23]One of the other surprising features is, this animal has broad
[03:26]ribs that overlap one another. And that's a feature we see
[03:30]in animals that may live in very shallow water, where their body
[03:34] would be compressed under the force of gravity, or even an animal
[03:38] that comes on land.
[03:39]Yet all those features are in an animal that still has scales,
[03:43]which is a very fish-like feature. So we're seeing some features
[03:47]which show its ancestry in fish, but other features which are
[03:51]reminiscent of animals like the earliest tetropods.
[03:54]All right. So I guess the key question here is what's
[03:56]the significance in terms of understanding more about evolution?
[04:02]Well, we know the broad structure of the tree of life,
[04:07]and many of the branches on that tree, including the tree
[04:11]of all limbed animals -- so that's everything from frogs,
[04:13]to dinosaurs, to us. We can see that they converge back
[04:18]in time to one point. And in the case of the limbed animals,
[04:23]we see that the earliest limbed animals existed in the late
[04:26]part of the Devonian period. That's about 365 million years ago.
[04:32]And we knew that those features of those earliest limbed animals,
[04:37]we also saw some of them in fishes and assumed that there
[04:41]was an evolutionary transition from those fishes to early
[04:44]tetropods, but we didn't have a really good transitional form,
[04:49]an intermediate, to show us how those features were acquired.
[04:53]And Tiktaalik fills that gap. It teaches us a lot about
[04:58]how the features which the earliest tetropods would use to
[05:02]build a limb and eventually come on land were first established
[05:06]in fish living in shallow water.
[05:09]Now tell us how you found this. Where did you find
[05:12]it and how did you know where to look?
[05:14]I work closely with Dr. Neil Shubin at the University
[05:17]of Chicago. And many years ago, he and I were trying to
[05:21]expand our field area. We were working in Devonian-age rocks
[05:25]here in Pennsylvania, but we wondered where else in North
[05:28]America we might be able to find rocks of that age,
[05:31]and rocks that were formed in the right kinds of environments,
[05:35]in this case shallow stream systems.
[05:38]And we learned that up on the -- on Ellesmere Island
[05:41]in the high Canadian Arctic, there were rocks that fit
[05:44]those criteria. So we did the geologic homework,
[05:47]we talked to geologists who had been in the area,
[05:50]and then we just went. And we looked.
[05:52]And there's nothing to substitute for getting your feet on
[05:55]the ground and your nose up to the rock
[05:57]and looking for these fossils.
[05:59]And it wasn't easy. We spent four years there --
[06:02]excuse me, we spent four summers there so far.
[06:06]And it wasn't until the last summer that we really hit
[06:09]it big with some of these very well preserved specimens.
[06:12]Although we have found numerous other kinds of fossil fish.
[06:16]And does the eureka moment happen in the field,
[06:20]or back in the lab, or is there even a moment
[06:22]when you say, wow, we've really come up with something?
[06:25]Well, there is actually a lot of eureka moments.
[06:28]And that's what is so exciting about exploration
[06:31]and discovery. Indeed, when we are in the field,
[06:33]we begin to see fragments, especially on the surface.
[06:37]We explore and try to find where those fragments
[06:40]were coming from -- in other words, what layer were
[06:42]producing those fragments. And then we dig in.
[06:45]We begin a small excavation. And if we find things
[06:48]that are more well preserved while we're digging
[06:50]on that layer, then we can do a full-scale excavation.
[06:54]But we wrap up what we find in a plaster jacket.
[06:57]It's like a cocoon, with plaster on the outside
[07:00]and rock and fossil bone on the inside. So we know
[07:04]we have something good, but we haven't seen all
[07:06]the details yet.
[07:07]And it's when we get that back to the preparation
[07:09]lab here in Philadelphia or in Chicago that very
[07:13]fine-scale work is done to expose all the features,
[07:17]to see just what the skeleton is like after the rock is
[07:21]removed. And that can take a lot of time, but it takes
[07:26]that much to get a good look and to carefully study what's there.
[07:30]All right, Ted Daeschler, thanks for describing it to us.
[07:33]My pleasure, thank you.