Science Friday - Ancient Iguanas Floated 5,000 Miles Across The Pacific | A Pregnant Ichthyosaur Fossil

Episode Date: May 6, 2025

Millions of years ago, iguanas somehow got from North America to Fiji. Scientists think they made the trip on a raft of fallen vegetation. Also, the marine reptile’s fossilized fetus is cluing paleontologists into the lives of ancient sea creatures.Ancient Iguanas Floated 5,000 Miles Across The PacificIf you picture iguanas, you might imagine them sunbathing on hot sand in the Caribbean or skittering around the Mojave Desert. But far, far away from where these iguanas are found is another group of iguanas living on the islands of Fiji and Tonga in the South Pacific—closer to New Zealand than the Americas. And it raises the question: How in the world did these iguanas end up all alone, on the other side of the ocean? In a study published in Proceedings of the National Academy of Sciences in March, scientists suggest that millions of years ago, iguanas hitched a ride on a raft and accidentally sailed all the way across the ocean before washing ashore and starting a new life. Host Flora Lichtman discusses the iguanas’ intrepid adventure with lead author Dr. Simon Scarpetta, evolutionary biologist and assistant professor at the University of San Francisco in California.Meet Fiona, The Pregnant Icthyosaur FossilIn the Patagonia region of Chile, Torres del Paine National Park is a graveyard of ichthyosaurs—ancient, dolphin-like reptiles that roamed the oceans when dinosaurs dominated the land. Nearly 90 of these giant reptiles’ fossils have been found amongst the glaciers. But the standout in the bone heap is Fiona, an ichthyosaur that lived 131 million years ago. She’s in pristine condition, the only fully preserved ichthyosaur in Chile. And, she died pregnant. She’s teaching paleontologists about the evolution of her species. And some of those findings were recently published in the Journal of Vertebrate Paleontology. Host Flora Lichtman talks with lead author Dr. Judith Pardo-Pérez, paleontologist at the University of Magallanes in Chile.Transcripts for each segment will be available after the show airs on sciencefriday.com. Subscribe to this podcast. Plus, to stay updated on all things science, sign up for Science Friday's newsletters.

Hey, it's Flor Lictman, and you are listening to Science Friday. On today's show, epic, ancient, seafaring, reptiles, and the people who go to the ends of the earth to study them. If you had to pick one organism that could really, really do this, it would really be iguanas. They're tough, tough as nails. If you picture iguanas, you might imagine them sunbathing on the hot sand in the Caribbean or skittering around the Mojavee desert. But far, far away from where these iguanas, you might imagine them, sunbathing on the hot sand in the Caribbean. But far, far away from where these iguanas are found is another group of iguanas living on the islands of Fiji and Tonga in the South Pacific, pretty close to New Zealand. And it begs the question, how did these iguanas end up all alone on the other side of the ocean?

In the journal Proceedings of the National Academy of Sciences, scientists suggest that millions of years ago, iguanas hitched a ride on a raft and accidentally sailed. all the way across the ocean before washing ashore and starting a new life. Here to discuss this intrepid adventure is Dr. Simon Scarpetta, evolutionary biologist and assistant professor at the University of San Francisco in California. Simon, welcome to Science Friday. Hi, Flora. Thanks for having me. I'm really excited to be here. Simon, how far would these iguanas have traveled? So in the modern day, as the crow flies distance between the western coast of North America and Fiji,

is somewhere between 8,000 and 9,000 kilometers, so 5,000-ish miles, something around that. That feels long to me. Yeah, it's really long. It's quite long. What should I be picturing? In my mind, when I think about it, it's a big mat of vegetation

or some down trees that get knocked over by a storm or potentially even a tsunami. And there maybe are some iguanas in the trees or next to the trees, but however it happens, they or their eggs get caught up in all this vegetation, and then a series of ocean currents, you know, drift them out far into the ocean, and eventually they make their way to the South Pacific. This feels like a Disney movie, but like instead of an intrepid girl with her chicken, it's just iguanas.

It's iguanas making their way on their little flotilla from one place to the next. Is this a world-sailing record for a land animal? It is. So, yeah, that's of all of the known overwater dispersals, of which there are definitely others known, including in several other iguanas. This is the longest hypothesized one and by a decent amount to a few thousand miles or so. And so really what it gives us is information about just what is possible in the tree of life, just what animals and lizards in particular can do. And that's really, really incredible. I mean, this feels so improbable to me.

How did you land on this hypothesis? Yeah. iguanas are a group of lizards that are currently found in the Caribbean and then in North America, especially in Central America, and then a bit into northern South America. And pretty much all of their close relatives are only found in the Western Hemisphere, too. And then you have this group of this Fijian iguanas that are found all the way out in the South Pacific really, really, really far removed. And so, you know, it begs the question. How could they have possibly gotten there? And one of the first results that I found that really caught my attention and then prompted further work was that the Fijian iguanas are most closely related to the North American desert iguanas that we have in Southern California and Arizona and then into northern Mexico. And their closest relatives are 5,000 miles away. Exactly, yeah. And on the western coast of the United States and Mexico specifically. Wow. Okay. So that's just genetics. It's like if their close relatives are over here, they must. have come from over here. Is that it? Well, that's definitely the first step towards getting there. So in addition to the genetic aspect, there's then dating the evolutionary tree of iguanas to try and

figure out, like, what's the most probable ancestral place from which the Fiji iguanas came, and then how is the mechanism by which they got there? And so those models found pretty conclusively that the most probable ancestral range would have been North America like you'd expect, and then the most probable mechanism would have been, you know, dispersal directly from North America to Fiji, rather than moving through some other route, like going through South America and then Antarctica and then up, or, you know, through Beringia, which is, you know, Alaska and eastern Russia, and then going all the way down through East Asia that way. Do these iguanas in the South Pacific, do they resemble the iguanas I would see in the desert in the southwest?

They do, yeah. Yeah, no, they have a lot of kind of surprising similarities to the desert iguanas that we have in the southwest. Very interestingly, they have some similarities in the morphology of the teeth that you don't generally see in other iguanas. Yeah, there's a lot of morphological similarities, but then some decided differences, too. So relative to all of the other iguanas and chuck wallas that are known, they're much more slender. They have these sort of a bit more compressed snouts, longer tails. The Fijian iguanas are these green, sort of resplendent, beautiful creatures, whereas the North American ones, also beautiful, in my opinion, but they tend to be a bit more drab to... More beautiful to an iguana scientist.

Yeah, more beautiful to an iguana scientist who likes going out in the desert and looking for lizards. Okay, I got to get back to the voyage, because I'm still mesmerized by it. How long would this voyage have taken, do you think? There have been a number of different estimates proposed for that, but maybe as short as two months and then maybe on the upper ends to a year. What were they eating? How did they survive? No, great question. And that's one of the other really cool things about the story, is that if you had to pick one organism that could really, really do this, you know, lizards in the general sense

would be a great option. And then within lizards, if you had to pick one that would just be the best candidate, it would really be iguanas. So they have kind of a lot of organismal traits. that I think predispose them to being able to, you know, survive these long-distance journeys. Why? Yeah. One is that they're large. So they have a decent amount, you know, of mass to work with and to lose. Two is that their metabolism is something called ectothermic, which is often called cold-blooded.

And so basically what that means is that they don't use a lot of energy to maintain a standing body heat like mammals and birds do. and so, you know, it means that they have to eat a lot less, but there's other stuff, too. So iguanas are also, you know, predominantly herbivorous, though they do consume insects and small other things occasionally. So they could eat their raft. Exactly. That's exactly it. They could potentially even eat their raft.

And then on top of that, you know, some species are pretty resistant to heat. You know, they're resistant to starvation. And then some of the species are also pretty resistant to dehydration too. So again, especially those that live in the desert. But that said, you know, obviously they could get some fresh water from eating the plants, but they could also conceivably get some fresh water from dew and things like that that would collect on a raft in the morning. Man, they're tough.

They're tough creatures, yeah. They're tough, tough as nails. You know, this story really changed my perception of iguanas. I'm glad to hear it. I mean, I think I thought of them. I'm actually scared to say this to you as an iguanas. for it. On iguanistan. I thought of them as like, I don't know, just kind of like sunbathing, like hanging in the sand plopped out. You know what I mean? Yeah, no, of course. And this study is

making me think I just, I've completely misunderstood them. Well, you know, they do like to hang out in the sun. It's true. And they do kind of plop, especially the bigger species, honestly. The green iguanas that probably most everyone is most familiar with, they're kind of vibing a bit. But it's also like a work hard, play hard or something. You know, like they go hard on vacation, but it seems like they, I don't know what the right, I need the right catchphrase for them. But they don't just plop is what I'm learning. Yeah, no, the plopping is interspersed with doing things that are difficult or incredible

or surviving hard conditions. And then when the times are chill, they just get to hang out. Work hard, play hard. That's how we want us do it. Simon, thanks so much for joining me today. Yeah, of course. Thanks for having me, Flora. It's been a pleasure. Dr. Simon Scarpetta is an evolutionary biologist, an assistant professor at the University of San Francisco in California.

Do not go away because coming up after the break, how a paleontologist found the fossil of a lifetime, a pregnant ichthyosaur. And I just got this what I call the ichthyosaur fever. When you get mad and peace out with everybody and you're jelloing or jelloing. And I started and I went alone to look up for ectiosaurus. In the Patagonia region of Chile, Torres del Pajene National Park is a graveyard of ichthyosaurs, ancient dolphin-like reptiles that roamed the oceans when dinosaurs dominated the land. Nearly 90 of these giant reptiles fossils have been found amongst the glaciers. But the standout star in the bone heap is Fiona, an ichthyosaur that lived 131 million years ago.

She's in pristine condition, the only fully preserved ichthyosaur in Chile, and she died pregnant. She's teaching paleontologists about the evolution of her species, and some of those findings were recently published in the Journal of Vertebrate Paleontology. Joining me to discuss is the lead author, Dr. Judith Pardo Perez, paleontologist at the University of Magajanas in Chile. Judith, welcome to Science Friday. Thank you very much. Thank you very much for the invitation. Judith, you discovered Fiona. Is that right? Yes, it was in 2009. Did you know you had something big the minute you laid eyes on her? Yes, no, the first day when we saw it, because the day when we found her, it was a crazy day because we were there almost three months.

And the last day, it was kind of pissed out because I have been in this area since 2004. And every single year we have been there, we have found ectiosaur. And that was the only year that we haven't found any new ectiosaur. and we were there for three months. So I say, okay, we have to look for ectiosaurs, and this is the last day. We have to find something new. And then we started exploring, and I just got this,

what I called the ichthyosaur fever, when you get mad and peace out with everybody, and you're jelloing. And I started, and I went alone to look up for etiosaurs, and the guys were coming afterwards with me. And then when we were walking in the area that day, we found five ichthyos hours, actually, five new ichthios hours. And one of them, the last one, was Fiona.

We look at, like, from a far distance, and we saw a very large black mark. And when we approached it, we were very amazed because she was completely exposed so we could see entirely from the skull until her tail. And we came back afterwards in the next year, in 2010. So that year, I took a transparent plastic foil and I put it over the bones and I started

to drawing the bones of the Xtiosar. And drawing it, I saw very tiny little vertebrine between the ribs and I realized that she was pregnant and has a baby and that she was a female, ectiosar. So that was the discovery. It's amazing. It's like you manifested the find. Yeah. Actually, the next year, when we came back in 2010, I was in my tent in the morning and I say, okay, we have found several ectiosaur. I found a completely exposed to an ectiosar. Now I want to find a pregnant nectiosar. It's like I say it to the universe. And then that morning we realized that the ectiosar was pregnant. You ask and the fossil gods deliver, I guess. Yeah. So she died pregnant, which like seems very cool to me as a layperson. But what can you learn from this?

In this area, we have the Aikosar that was pregnant, but we also have found several neonates, so a newborn and also other ectosars that are avals. So several newborns, avals, a lot of food. So we think that this area was an area where they came to give birth. Like a nursery? Yeah, like a nursery area. So in this period of time, in the history of fictiosaur's of what we know worldwide, we don't have information. So there is a gap in this time, which is during the early Cretaceous 131 million years ago. And that will help us to understand the evolution of fictiosaur. Wow.

Can we learn anything about how they gave birth? from looking at the fetus? Mm-hmm. They give bird with the tail first. So the last thing in going out was the skull because these were oxygen-breathing animals. So this is the case with Fiona. You can see that the baby was going to be prepared to be born.

But this is very interesting because the first Xikiosaurs, they were giving bird with the head first. So it means that. that it was maybe an evolutionary strategy to change that in order to have the tail going out first and the head, the last thing and not die during the process of giving birth. That's fascinating. Because basically you want to keep them because they can't breathe underwater. You want to keep their oxygen supply going for as long as you can before they're born. Yeah, yeah, because the anatomy of ectiosaurs, you know, they are very similar to dolphins.

They are not related. Itchiosars were marine reptiles and dolphins are marine mammals. But in anatomy, they are very similar because both animals live and were very adapted to live in the seas. Got it. Why did you name her Fiona? It was because during the process of excavation, we put a glue that we use to protect the bones because of the vibration of the machine that we were using. And when we were doing it, she turned green of green color.

And we were super scary because they say, oh, what's happening and why she's green? And she's supposedly not to be green. And everybody will be mad of me. And then we stopped to analyze what is happening. And with the magnified glasses, we observed that there were little plants that were living in between the cracks. and gave her this green color. So after that, we washed it with acetone,

and then she came back to the normal color. So that night, we started to draw names, and then Dr. Henry Maxwell from the Natural History Museum of Stuttgart, she said, oh, maybe it can be Fiona for Fiona of Shrek, you know. And everybody liked it. From Shrek. Yeah. It's perfect.

Yeah, it's perfect. Give me a sense of a day in your life when you're on an expedition. Yeah, you know, expeditions here in Patagonia are very extreme because it requires a lot of logistics. So we drive the car for hours until the national park. And then we have to walk nine hours until the area where we camp. And the horses take some of the loads and we walk. and the helicopter take the heaviest low. So and in the camp, you try to take data and to not dive, of course,

because the weather is very complicated. Also, it's cold even in summer. You can have snow. Winds is also extreme. So taking data every day, it's very demanding, a lot of work. and for minimum a month, the expeditions that we go. Wow. Yeah.

And you were saying that you were on month three, you know, the end of three months for Fiona. Yeah. Yeah. That's a long time. That's a way of life. Yes. Yeah, but we really like it. We still have ichthyosar there that we need to excavate because the ictiosaurs are getting very damaged because of the erosion on the area.

So they are going to be in a. very short time slowly destroyed. So if we do not protect in C to the material and if we do not excavate them, we are going to lose it. And this is very something extremely, very important material worldwide. What are you looking for now? I would like to find more pragmatic users. That could be super cool because this will support our hypothesis. Oh, the nursery hypothesis.

Yes, yes. That would help us a lot. I love that. Well, good luck. Yeah. Thank you very much. Dr. Judith Pardo Perez is a paleontologist at the University of Magajanas in Chile. Judith, thanks so much for joining us today. Thank you very much, for the invitation. It was very nice. I agree. And that is about all we have time for. Lots of folks helped make the show happen, including Diana Plasker, Jordan Smudjick, Emma Gomez. Valissa Mayors. I'm Flora Lichten. Thanks for listening.