JOHN DANKOSKY, HOST:
This is SCIENCE FRIDAY. I'm John Dankosky, sitting in for Ira Flatow. This time of year, wildlife conservationists warn you to look out for migrating turtles crossing the road. OK, what if the turtle is nearly eight feet long, the size of a compact car?
Well, 60 million years ago, not long after the dinosaurs disappeared, this monster turtle was patrolling the tropics, snapping up fish and baby alligators in his powerful jaws. My next guest discovered this beast in a coalmine in Colombia, and he describes it in the Journal of Systematic Paleontology.
Let me introduce him. Edwin Cadena is a graduate student at North Carolina State University in Raleigh. He joins us from a studio in Raleigh today. Welcome to SCIENCE FRIDAY, Mr. Cadena.
EDWIN CADENA: Thanks, hello, John, for the invitation to participate today in SCIENCE FRIDAY, and really it's a pleasure for me to be on NPR today.
DANKOSKY: Well, we're happy to have you here. If you want to give us a call, our number is 1-800-989-8255, that's 1-800-989-TALK. If you're on Twitter, you can tweet us your questions by writing the @ sign followed by scifri.
So first of all, tell us how you found this thing. Why were you looking at a coalmine for a giant turtle?
CADENA: Yeah, well, the story starts actually around 2005, when a colleague of mine, he's a paleobotonist, went to the mine for the first time, and he found some fossil leaves. And that was the first clue for looking for something else. We said if we find fossil leaves, maybe there are more things there.
And I went to the mine to collect everything that was on the field, and in particular we were focused on the bones, so fragments of animals. And so the story started in 2005, when I started discovering turtles and pieces of bone of turtles and also fragments of crocodiles. And even for that time, I had the opportunity to discover the first vertebrae of titanboa, the largest snake so far known.
And so it's been fascinating since 2005, going to this mine in Colombia looking for fossils.
DANKOSKY: And what were you using to dig around in this coalmine?
CADENA: So basically I call it the high-tech paleontology, but it's actually very simple tools. We used screwdrivers, and the screwdrivers are fantastic tools for - in particular for the rock of the mine, which is clay stone, and they - using the screwdriver, we can easily break down pieces in order to preserve and be able to extract the fossils carefully. So the screwdriver is a fantastic tool for me.
DANKOSKY: It doesn't sound like exactly the right tool, but if it gets the job done, you know, whatever it takes. So you found other turtles down there. When did you start to realize you had something different on your hands?
CADENA: Yeah, so this is - Carbonemys, which is the turtle we are talking today, is the second species that we describe at the mine. We described another one in 2010. And - but this one is the largest one that we have found in the mine, and it was a really exciting day for me.
It was in January 2006, actually, a couple days after my birthday, and I went to - very early in the morning to one of the localities of the mine, this huge pit they built. And so I saw a small piece of bone on the ground, in the rock, and I started using, well, the screwdriver, and it took me almost two days actually to realize how big was and to see, oh my God, this is something new, this is something that we haven't seen in Cerrejon, but also it's something new in terms of evolution of turtles, and the size was gigantic. So that was a really cool moment for me.
DANKOSKY: Well, let's talk more about the size. I mentioned it's about as big as a compact car, but how big is its shell? How big was its head?
CADENA: So yeah, the shell is around 173 centimeters long, but that's without adding - when we add the head and the neck and the tail, we easily can have a turtle around two meters, 20 centimeters long. So it's very, very similar to the size of a small car today. So it was a really large - really large animal.
DANKOSKY: So what do you know about how this turtle lived, what it ate, all that stuff?
CADENA: So another important thing about Cerrejon or this locality in Colombia is that for the first time in the fossil record, we can have some sort of idea of the entire ecosystem of the tropics or the neo-tropics after the extinction of dinosaurs. So - because the fossil leaves, we had the plants, we had the fruits and also we had the animals.
So we can reconstruct the entire ecosystem of the tropics, and we know, for example, that turtles and in particular Carbonemys is, the design, the configuration of the bones of the head are very - I mean, it's possible that this configuration, the massive maxillary bone, which is actually a bone that turtles use for masticatory process, they were huge, and that implicates that probably this turtle was eating not only plants but also on the menu could be small crocodiles or small turtles, too.
DANKOSKY: And what you're talking about the masticatory process, you mean like chewing its food.
CADENA: Yes, yes, absolutely.
DANKOSKY: We're talking with Edwin Cadena, who found, well, this enormous prehistoric turtle. And if you want to ask any questions, 1-800-989-TALK, 1-800-989-8255. So you think even small crocodiles were something on the menu for this turtle?
CADENA: Yeah, absolutely, if - and actually when we're considering the size of this turtle, well, menus like crocodiles or meat could be beneficial for growing so - because it has a lot of protein on it. So we had - are pretty sure that - I mean, that configuration of the head, it matched perfectly with eating crocodiles.
DANKOSKY: I want to go to a phone call here. Yuri(ph) is in Charleston, South Carolina. Hi there, Yuri.
YURI: How are you doing?
DANKOSKY: What's on your mind?
YURI: I just wanted to know what was the largest that had been found prior to this discovery, comparatively speaking.
DANKOSKY: Great question.
CADENA: Yeah, that's a very good question, and I want to point out here because this is not the largest freshwater turtle so far known. The largest turtle, freshwater turtle so far known is from Venezuela and Brazil. But it's only seven million years old.
And we're talking about a turtle almost similar size to Stumpendemys, the biggest freshwater turtle so far known, but 50 million years older. So it's a fascinating story about how the body size in turtles evolved in the last 50 million years.
DANKOSKY: Now it's not just the body size in turtles, though. As you mentioned earlier, you found a giant snake in almost exactly the same place a few years back. What's in the water there? Why all these big animals?
CADENA: So yeah, that's really interesting about Cerrejon is also for the first time in the fossil record, we are able to test many hypotheses and many ideas that actually biologists and ecologists today have, as for example how the (unintelligible) evolved in reptiles.
And (unintelligible), I think there are only one reason to explain why these animals get so big after the extinction of dinosaurs, and probably there are at least three factors involved in this. The first is big ecological change between the Cretaceous, when you had on land dinosaurs, and probably the ancestors of turtles, snakes, all these animals were sharing the environment with dinosaurs, probably competing for food, or even some of them could be actually the prey for dinosaurs.
That happened on land, but also you were in water. You were a turtle that was living very close to the sea, very close to the coastal areas. You probably meet some of these marine reptiles like (unintelligible). They were killers. So a big change in ecology comparing to the Cretaceous versus the Paleocene in Colombia, when you don't have the dinosaurs on land anymore, but marine reptiles anymore on the seas.
So that's a good opportunity for these reptiles to have more space, more sources of food. So that's one of the first factors to consider (unintelligible). The second one is also a race between predator and prey. So if a turtle increased its size so potentially the crocodiles also had to increase their size to be able to (unintelligible).
And we have evidence in the shells, in the carapace of these turtles, that there were bite marks from crocodiles. So we know that crocodiles from Cerrejon were eating these turtles, too. So it's another factor here.
And the last one is related to the climate. And we know based in the fossil record of plants, and also we use the body size of reptiles to estimate how was the temperature for that time, and we know that it was much, much warmer than any tropical environment today, around four or six degrees Celsius warmer.
And that's beneficial for reptiles for increased size and also for facilitating growth.
DANKOSKY: So that's some real global warming. We're getting lots of questions from people. One thing they want to know is how fast could this thing move. Is there any way to know?
CADENA: Well, it's really difficult to make an estimation on how fast they move because we don't have any forelimbs. So we don't have the arms or the legs to actually have an idea of the locomotion of this animal. But my idea is that this probably could be a turtle that instead of walking or swimming far distance preferred to see on the bottom of the lakes or the river waiting for the prey. So it probably wasn't too fast.
DANKOSKY: And just so the people can picture what this looked like, is it like the box turtle that you have at home, and it's just a really big size, or what did it look like?
CADENA: Yeah, I mean, a good example of - or to have an idea is - they are like an alligator turtle, for example, but much, much bigger than that one. So that's a good example of how Carbonemys looked like.
DANKOSKY: So one last thing for you here: Do you think that reptiles could ever get bigger like this once again? Is this ever going to happen again in history?
CADENA: Yeah, that's the cool story behind this discovery, too, that actually the predictions currently show - many biologists predict that based on the conditions that we have today, the climate change, most of the tropical reptiles, they're going to be extinct. So they are going to disappear.
But maybe, the fossil record can tell us that actually these animals can be - adapt to these different conditions and temperature very easily. So I'm pretty sure - I mean, I say the conditions now are relatively different to 60 million years old because had less areas, and we humans are here, so I'm pretty sure some of this is (unintelligible). I'm pretty sure someone is going to get it.
So but yeah, I mean, it is potentially - the temperature start - I mean, continue increasing, we will be expecting to see again these gigantic reptiles on the tropics.
DANKOSKY: Edwin Cadena is a graduate student at North Carolina State University in Raleigh. Thanks for joining us and for sharing this amazing discovery.
CADENA: Well, thanks a lot.
DANKOSKY: Now, coming up after the break, how humans became the super-omnivores we are today and the universal appeal of crunchy foods. Stay with us. Transcript provided by NPR, Copyright NPR.