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

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.

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:00Flora Lichtman?

  Science Friday is supported by Dell. Gifts mean more when they have the power to unwrap more of who you are. This Black Friday, give a gift that goes beyond the box. The Dell XPS 13 laptop. It's the thinnest, lightest XPS laptop yet with a long battery life, beautiful design, and powerful performance with Intel Core processors. The XPS laptop unlocks more of what you love. Plus, at dell.com, you'll find perks like Dell Rewards, fast free shipping, and flexible financing, and big savings on monitors and accessories. Head to dell.com/deals. That's dell.com/deals.

• 0:46Ira Flatow?

  Science Friday is supported by MathWorks, creator of MATLAB and Simulink software for technical computing and model-based design. MathWorks, accelerating the pace of discovery in engineering and science. Learn more at mathworks.com.

• 1:03Speaker 02

  Support for Science Friday comes from USA for UNHCR, the UN Refugee Agency. Here's a problem. How do you keep a house above freezing when the windows are gone and the power is out for 16 hours a day? In Ukraine this winter, the answer fits in a box. Reflective insulation, plastic sheeting to cover broken windows, draft blockers for the doors. Simple materials installed the same day a team arrives. Your gift delivers them, and until December 31st, it's matched. Donate at unrefugees.org/friday.

• 1:40Speaker 03

  WNYC is supported by Bear. Science is about asking questions, testing, trying again. It's not easy, but it's relentless. It evolves, and that's why science delivers. Learn more at sciencedelivers.com.

• 1:58Flora Lichtman?

  Hey, it's Flora Lichtman, 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.

• 2:09Speaker 04

  If you had to pick one organism that could really, really do this, it would really be iguanas. They're tough, tough as nails.

• 2:20Flora Lichtman?

  If you picture iguanas, you might imagine them sunbathing on the 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, 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.

• 3:04Flora Lichtman?

  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.

• 3:15Speaker 04

  Hi, Flora. Thanks for having me. Really excited to be here.

• 3:18Flora Lichtman?

  Simon, how far would these iguanas have traveled?

• 3:21Speaker 04

  So in the modern day, the "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.

• 3:37Flora Lichtman?

  That feels long to me.

• 3:38Speaker 04

  Yeah. It's really long. It's quite long.

• 3:42Flora Lichtman?

  Like, what should I be picturing?

• 3:44Speaker 04

  In my mind, when I think about it, it's, you know, a big, matte vegetation or some downed 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.

• 4:11Flora Lichtman?

  This feels like a Disney movie, but like, instead of an intrepid girl with her chicken, it's just iguanas.

• 4:17Speaker 04

  It's iguanas making their way on their little flotilla from one place to the next.

• 4:21Flora Lichtman?

  Is this a world sailing record for a land animal?

• 4:24Speaker 04

  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, too, 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 it's really, really incredible.

• 4:49Flora Lichtman?

  I mean, this feels so improbable to me. How did you land on this hypothesis?

• 4:55Speaker 04

  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 these 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, you know, 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,

• 5:39Speaker 04

  and then into Northern Mexico.

• 5:41Flora Lichtman?

  Their closest relatives are 5,000 miles away.

• 5:44Speaker 04

  Exactly, yeah. And on the western coast of the United States and Mexico specifically.

• 5:50Flora Lichtman?

  Wow, OK, 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?

• 5:57Speaker 04

  Well, that's definitely the first step towards getting there. So in addition to the genetic aspects, 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 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

• 6:42Speaker 04

  through East Asia that way.

• 6:44Flora Lichtman?

  Do these iguanas in the South Pacific Do they resemble the iguanas I would see in the desert in the southwest?

• 6:51Speaker 04

  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 chuckwallas 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, you know, 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...

• 7:31Flora Lichtman?

  More beautiful to an iguana scientist.

• 7:34Speaker 04

  Yeah, more beautiful to an iguana scientist who likes going out in the desert and looking for lizards.

• 7:40Flora Lichtman?

  Okay, I gotta get back to the voyage, because I'm still mesmerized by it. How long would this voyage have taken, do you think?

• 7:47Speaker 04

  There've been a number of different estimates proposed for that, but, you know, maybe as short as two months and then maybe on the upper end to a year.

• 7:54Flora Lichtman?

  What were they eating? How did they survive?

• 7:57Speaker 04

  Yeah. No, great question. So, 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.

• 8:23Flora Lichtman?

  Why?

• 8:24Speaker 04

  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.

• 8:58Flora Lichtman?

  So they could eat their raft.

• 8:59Speaker 04

  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.

• 9:28Flora Lichtman?

  Man, they're tough.

• 9:30Speaker 04

  They're tough creatures, yeah. They're tough, tough as nails.

• 9:32Flora Lichtman?

  You know, this story really changed my perception of iguanas, like...

• 9:37Speaker 04

  I'm glad to hear it.

• 9:38Flora Lichtman?

  I mean, I think I thought of them, I'm actually scared to say this to you, as an iguana...

• 9:44Speaker 04

  No, go for it.

• 9:45Flora Lichtman?

  ...an iguanastan. 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?

• 9:56Speaker 04

  Yeah, no, of course.

• 9:57Flora Lichtman?

  And this study is making me think I just, I've completely misunderstood them.

• 10:02Speaker 04

  Well, you know, they do like to hang out in the sun, that'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.

• 10:14Flora Lichtman?

  But it's like, it's also like a work hard, play hard or something, you know, like they, they go hard on vacation, but it seems like they, I don't know what the right, any of the right catchphrase for them, but...

• 10:24Speaker 04

  No, no.

• 10:25Flora Lichtman?

  They go just plop, is what I'm learning.

• 10:27Speaker 04

  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 iguanas do it.

• 10:40Flora Lichtman?

  Simon, thanks so much for joining me today.

• 10:41Speaker 04

  Yeah, of course. Thanks for having me, Flora. It's been a pleasure.

• 10:44Flora Lichtman?

  Dr. Simon Scarpetta is an evolutionary biologist and assistant professor at the University of San Francisco in California.

• 10:54Flora Lichtman?

  Do not go away because coming up after the break, how a paleontologist found the fossil of a lifetime, a pregnant ichthyosaur.

• 11:03Speaker 05

  And I just got this, what I call the ichthyosaur fever, when you get mad and pissed out with everybody and you're jelling, you're jelloing. And I started and I went alone to look for ichthyosaurs.

• 11:21Speaker 03

  Science Friday is supported by PBS, presenting Going Wild. If you love learning about the natural world and meeting the scientists who help us understand it, be sure to check out the new season of Going Wild with Dr. Ray Wynn Grant. It's the chart topping and Webby Award winning podcast from the folks at Nature on PBS, now with a video companion series. In this season of Going Wild, host acclaimed wildlife ecologist, Dr. Ray Wynn Grant, heads out into the field to explore the animals, people, and stories that make nature worth saving. Stops include a hibernating black bear den in Arkansas and an underwater shipwreck site off the Florida coast. If you're looking for a place to start, check out the season's debut episode where Ray joins beloved biologist and influencer Jordan King in the Florida Everglades

• 12:05Speaker 03

  to learn about his unlikely journey into science and how to study a wetland when it's not very, well, wet. So don't miss out. Follow Going Wild with Dr. Ray Wynn Grant on Apple Podcasts, Spotify, YouTube, or wherever you get your podcasts.

• 12:19Flora Lichtman?

  Support for Science Friday comes from the William K. Bose Jr. Foundation.

• 12:27Flora Lichtman?

  In the Patagonia region of Chile, Torres del Payense 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.

• 13:11Flora Lichtman?

  Judith Pardo Perez, paleontologist at the University of Maga Janas in Chile. Judith, welcome to Science Friday.

• 13:18Speaker 05

  Thank you very much. Thank you very much for the invitation.

• 13:21Flora Lichtman?

  Judith, you discovered Fiona, is that right?

• 13:24Speaker 05

  Yes, it was in 2009.

• 13:27Flora Lichtman?

  Did you know you had something big the minute you laid eyes on her?

• 13:30Speaker 05

  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, I 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 ichthyosaurs. And that was the only year that we haven't found any new ichthyosaur. And we were there for three months. So I say, OK, we have to look for ichthyosaurs. And this is the last day, we have to find something new. And then we started exploring and I just got this, what I call the ichthyosaur fever, when you get mad and pissed out with everybody and you're yelling, you're jelloing.

• 14:10Speaker 05

  And I started and I went alone to look for ichthyosaurs and the guys were coming afterwards with me. And then when we were walking in the area that day, we found five ichthyosaurs, actually five new ichthyosaurs. And one of them, the last one, was Fiona. We look at it 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.

• 14:51Speaker 05

  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 ichthyosaur. And drawing it, I saw very tiny little vertebrae in between the ribs. And I realized that she was pregnant and has a baby. And that she was a female ichthyosaur. So that was the discovery.

• 15:20Flora Lichtman?

  That's amazing. It's like you manifested the find.

• 15:23Speaker 05

  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 ichthyosaurs, I found a completely exposed ichthyosaur. Now I want to find a pregnant ichthyosaur. It's like, I say it to the universe. And then that morning, we realized that the ichthyosaur was pregnant.

• 15:47Flora Lichtman?

  You ask, and the fossil gods deliver, I guess.

• 15:50Speaker 05

  Yeah.

• 15:51Flora Lichtman?

  So she died pregnant, which like seems very cool to me as a layperson. But what can you learn from this?

• 15:58Speaker 05

  In this area, we have the ichthyosaur that was pregnant, but we also have found several neonates, so newborn, and also other ichthyosaurs that are adults. So several newborns, adults, a lot of food. So we think that this area was an area where they came to give birth.

• 16:19Flora Lichtman?

  Like a nursery?

• 16:20Speaker 05

  Yeah, like a nursery area. So in this period of time, in the history of ichthyosaurs 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 ichthyosaurs.

• 16:45Flora Lichtman?

  Wow. Can we learn anything about how they gave birth from looking at the fetus?

• 16:51Speaker 05

  Mm-hmm. They give birth with the tail first. So the last thing in going out was the skull, because these were oxygen-breeding 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 ichthyosaurs They were giving birth with the head first. So it means that it was maybe an evolutionary strategy to to change that in order to to have the tail going out first and the head the last thing and not die during the process of giving birth.

• 17:35Flora Lichtman?

  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.

• 17:48Speaker 05

  Yeah, yeah, because the anatomy of ichthyosaurs, you know, they are very similar to dolphins. They are not related. Ichthyosaurs were marine reptiles and dolphins are marine mammals. But in anatomy, they are very similar because both animals live and were very adapted to to live in the seas.

• 18:08Flora Lichtman?

  Got it. Why did you name her Fiona?

• 18:11Speaker 05

  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, ah, what's happening and why she's green? And she's supposedly not to be green and everybody will be mad at 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.

• 18:50Speaker 05

  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. Mary 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.

• 19:12Flora Lichtman?

  From Shrek.

• 19:14Speaker 05

  Yeah.

• 19:14Flora Lichtman?

  It's perfect. Yeah, it's perfect. Give me a sense of a day in your life when you're on an expedition.

• 19:20Speaker 05

  Yeah, you know, expeditions here in Patagonia are very extreme because it requires a lot of logistics. So we, we drive the car for hours until the national park. And then we have to take, 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 heavy load. So, and in the camp, you try to take data and to not die, of course, because it's, it's, the weather is, is very complicated also. It's cold even in summer.

• 20:02Speaker 05

  You can have snow, winds, it's also extreme. So taking data every, every day is very demanding and a lot of work. And for minimum a month, the expeditions that we go.

• 20:18Flora Lichtman?

  Wow. Yeah. And you were saying that you were on month three, you know, the end of three months for Fiona.

• 20:23Speaker 05

  Um, yeah.

• 20:25Flora Lichtman?

  Yeah, that's a long time. That's a way of life.

• 20:27Speaker 05

  Yes. Yeah, but we really like it. And we still have ichthyocysts there that we need to excavate because the ichthyocysts are very, getting very damaged because of the erosion on the area. So they are going to be in a very short time, um, slowly destroyed. So if we do not protect in situ 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.

• 21:01Flora Lichtman?

  What are you looking for now?

• 21:03Speaker 05

  I would like to find more pregnant ichthyocysts. That could be super cool because this will support our hypothesis.

• 21:10Flora Lichtman?

  Oh, the nursery hypothesis.

• 21:11Speaker 05

  Yes, yes. That would help us a lot.

• 21:15Flora Lichtman?

  I love that. Well, good luck.

• 21:16Speaker 05

  Yeah, thank you very much.

• 21:19Flora Lichtman?

  Dr. Judith Pardo Perez is a paleontologist at the University of Magallanes in Chile. Judith, thanks so much for joining us today.

• 21:27Speaker 05

  Thank you very much, Clara, for the invitation. It was very nice.

• 21:30Flora Lichtman?

  I agree.

• 21:34Flora Lichtman?

  And that is about all we have time for. Lots of folks helped make this show happen, including Diana Plasker,

• 21:41Speaker 03

  Jordan Smudgic,

• 21:42Flora Lichtman?

  Emma Gomez, Velissa Mears. I'm Flora Lixman. Thanks for listening.