01/08/2021

Giant, Toothed Birds Once Ruled The Skies

16:51 minutes

an colored illustration of large seagull-looking birds with larger longer beaks with teeth. the flock flies over water
The pelagornithids once ruled the skies. Illustration by Brian Choo

More than 62 million years ago, a few million years after the extinction of non-avian dinosaurs, a group of seafaring birds known as pelagornithids first appeared in the fossil record. They had long wings, and, unusually for a bird, teeth. They had a much  simpler structure than modern mammal teeth, known as pseudoteeth. 

a diagram of a bird skull with teeth and below it a small jaw fossil bone, showing where it would fit in the bottom half of the beak
A reconstruction of the skull of one of these birds and where the discovered jaw fragment would fit into it. Credit: Peter Kloess

While alive, pelagornithids successfully took over the planet. Their remains have been found on every continent, and their existence stretched for more than 50 million years. New research, published in Scientific Reports late last year, reveals that by the time the pelagornithids had been around for 12 million years, they’d already evolved to gigantic sizes never seen since in birds. They had 6-meter wingspans, nearly twice the size of modern albatrosses.

SciFri producer Christie Taylor talks to Peter Kloess, a co-author on the new research, about these giants of the past, plus the mystery of the pelagornithids’ disappearance.


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Segment Guests

Peter Kloess

Peter Kloess is a PhD candidate in the Department of Integrative Biology and Museum of Paleontology at the University of California-Berkeley in Berkeley, California.

Segment Transcript

IRA FLATOW: This is Science Friday. I’m Ira Flatow. Last week we celebrated the annual Christmas bird count and the way citizen scientists, out in the field or at home, can help us understand the extinction threat the climate crisis poses to our feathered friends. This week we follow up to talk about the birds that are already extinct, and the mysteries scientists are trying to solve about their disappearance. Science writer/producer Christie Taylor is on the case.

CHRISTIE TAYLOR: You won’t see a pelegornathid bird today. But a long time ago they were everywhere, at least as far as the fossils suggest. These long-winged fliers lived millions of years ago in the gap between the extinction of non-avian dinosaurs and now. In fact, they were around for more than 50 million years and grew to truly gigantic sizes compared to modern birds. And then, they too disappeared.

With me today is Peter Close, a PhD candidate in integrative biology at the University of California Berkeley. He’s also at the Museum of Paleontology there. And he’s co-author on some new research looking at fossils from the museum that say something about just how quickly these birds became the giants that we know them as. Welcome to Science Friday, Peter.

PETER CLOSE: Hi. Thank you very much for having me.

CHRISTIE TAYLOR: Yeah. It’s great to have you. I feel like the first thing we need to talk about is introducing our main character, which in this case are these birds called the pelegornathids. I’m picturing huge albatrosses right now. But I don’t think that’s quite right. So tell me about them.

PETER CLOSE: Well, thinking of albatrosses is actually a great place to start in the sense that they have these long wingspans. As they would have been flying through the air, they would have kept their wings out, soaring long distances, covering vast tracts of water. Where they differ from albatrosses is their most prominent feature.

These pelegornathids are also known as bony-tooth birds. And as that name implies, they have these projections out of their jaws that, at a very superficial level, look like teeth. So if you think of an albatross on steroids with teeth, you’re actually in the right ballpark for getting a mental picture of this group.

CHRISTIE TAYLOR: Wow. And they lived a pretty long time ago, right? So we’re talking millions and millions of years ago.

PETER CLOSE: Oh, yes. Yes. The oldest member of this family of birds dates to about 62 million years ago, comes from New Zealand. And the youngest members of this group are in that 3 to 2 million year age range. So this group existed for at least 60 million years of Earth history.

CHRISTIE TAYLOR: In this paper that we’re here to talk about today, you and your co-authors took a look at a couple of fossils from these pelegornathids. And you learned something new about them. How did that work?

PETER CLOSE: So my colleagues and I were looking around the University of California Museum of Paleontology and came across these specimens that had been collected decades before, in the 1980s, from Antarctica. And one of these specimens was a fragment of jaw with those very iconic pseudo teeth, as we call them, or false teeth. And so we knew that we had a pelegornathid here on our hands.

But in digging into some of the history of that specimen, we also started looking at the other related pelegornathid specimens from Antarctica. And the combination of those specimens showed us that the evolution of gigantism in this whole family occurred earlier than was originally thought.

CHRISTIE TAYLOR: How much earlier?

PETER CLOSE: So we’re talking about 50 million years ago. And if you think about it in the context of that oldest known pelegornathid from about 62 million years, that puts this instance of gigantism occurring about 10 to 12 million years after the oldest known individual. So that gives us this notion that this group of birds grew to gigantic sizes and not too long after they first appeared.

CHRISTIE TAYLOR: I want to talk about the difference between a regular sized pelegornathid and this giant size. What is the difference we’re talking about, how many feet?

PETER CLOSE: Yeah. So when we’re talking about that oldest pelegornathid from 62 million years, this is a bird with a wingspan that’s estimated about three feet, so something like your modern gull. There are plenty of individuals that we could call large in the right around 4 meter wingspan. So that’s about 13 feet.

CHRISTIE TAYLOR: OK.

PETER CLOSE: And then our giant individuals, which– the specimens that we identified from Antarctica and some other specimens from around the world, these ones are getting up to 6 meters in wingspan. So that’s about 20 feet long.

CHRISTIE TAYLOR: Yeah.

PETER CLOSE: Yeah.

CHRISTIE TAYLOR: Yeah.

PETER CLOSE: Another way to think about it is, if you took a two-story building, turn it on its side, and that’s about 20 feet long. So the evolution of the giant size, that six-ish meter wingspan, occurred about 10 to 12 million years after the first pelegornathid known.

CHRISTIE TAYLOR: And you figured this out just from a jawbone and part of a foot, I think you said. How do you look at fossils and place them in time in that way, especially when you aren’t the one who found them?

PETER CLOSE: So these specimens– as I had mentioned, they were collected in the 1980s. A team primarily from the University of California at Riverside in Southern California– they traveled to Antarctica. And there they were observing the geology as well as collecting lots and lots of fossils. While they were there as they’re looking at the geology, they’re taking lots of field notes, they’re getting a sense for, basically, where in time these specimens are coming from. And it’s those notes that came back to the United States with these specimens.

In 2003, the collection from UC Riverside made its way up to Berkeley, where I’m at right now. So to place these specimens in time, that’s where we go back to the field notes to understand, what geology was that team looking at? And what stratigraphic horizons where they working in?

So the foot bone, the one that comes from a giant individual from about 50 million years ago– in previous papers, the specimen had been described before. But it had been placed higher in the geologic section, which we can just think of as meaning younger in section. And my colleagues and I, when we went back to the original field notes, that’s when we realized that it should have been lower in the section, or older in time, 50 million years ago.

CHRISTIE TAYLOR: So you keep talking about pseudo teeth. What are pseudo teeth? And what makes them different from teeth teeth?

PETER CLOSE: Yeah. So when we talk about pelegornathids, we use the term pseudo teeth, which means false teeth. These are not true teeth as you or I have, or any of us have, in our jaws at the moment. Our teeth are made of material such as enamel and dentin and some other things. And they’re rooted with tooth roots into sockets in our jaw.

These pelegornathids didn’t have any of that. These bony projections– as I just said, they’re bony. They are fused directly to the bone and the jaw. And they’re not made of enamel and dentin. They’re composed of bone and, much like bird beaks today, would have been overlain with a keratin sheath. And keratin is the same material that we have in our fingernails and our hair.

So instead of making teeth of enamel and dentin, these pelegornathids have pseudo teeth of bone and keratin, a much different configuration than we’ve got now.

CHRISTIE TAYLOR: And I want to go back to the part where these bones were in a museum collection. And I think we think of all of the new science in fossil finds coming from those dramatic, you dig it up and you immediately look at it and understand it. But this was a situation where the science was sitting in a museum waiting to be found there. Is that common in your field?

PETER CLOSE: Yeah. I think that can be pretty common. I’ve participated in many dinosaur digs. And those are certainly wonderful places to make discoveries. Generally when we think of museums, we’re thinking of those public exhibits and the displays.

What we see on display and in exhibits really only represents a fraction of what most museums have in their collections. I couldn’t even begin to throw out a number because it will differ for each museum.

CHRISTIE TAYLOR: I’m picturing the big room at the end of “Indiana Jones,” giant warehouses full of dinosaur bones.

PETER CLOSE: That scene in “Indiana Jones”, at least for some museums, is not that far off. Some repositories just have shelves and shelves and rows upon rows of crates and casts and sediment that needs to be worked through. That’s one of the beauties of museums is that you have this wealth of material that curators and collection managers, museum staff– they only have so much time during the day to work on these things. While they’re making their own discoveries, there’s many more specimens that are left sitting for decades, just waiting for some grad student like myself to come along and to work on them.

Museums are wonderful. From the public side of things, we can make discoveries in the exhibits. But from the research side of things, the collections are just full of opportunity.

CHRISTIE TAYLOR: I can’t help but go back to the fact, also, that these giant birds were found in the sediment in Antarctica. I forget sometimes that there’s rock in Antarctica and that there’s a whole fossil record there. What else was going on in Antarctica 50 million years ago when we had these giant birds? What was that part of the planet like?

PETER CLOSE: So this is 50 million years ago. This is within a period that we call the Eocene. During the Eocene, the entire planet was much warmer than it is today. But in particular, in Antarctica, if we think of Antarctica today, we’re thinking of large ice sheets and penguins and large flocks puttering around and ice flows.

But in the Eocene, Antarctica was much, much warmer than it is today. Fossils have been found of marsupials and relatives of sloths and anteaters.

CHRISTIE TAYLOR: Wow.

PETER CLOSE: The birds that were there, outside of our pelegornathids– penguins were there, just like they are today. But you also had ducks and large ostrich relatives. Just in the beginning part of 2020, the first fossil frog was discovered.

CHRISTIE TAYLOR: What?

PETER CLOSE: Yeah.

CHRISTIE TAYLOR: That’s a pretty warm climate if you have amphibians there.

PETER CLOSE: Exactly. Yeah. To have to have a fossil frog there, it had to have been so much warmer than we think of today.

CHRISTIE TAYLOR: Just a reminder that this is Science Friday and I’m Christie Taylor. In case you just joined us, we’re talking about giant birds of the past and what fossils are teaching us about them. And Peter Close, what else do we need to know about these giant, toothed birds that used to live in Antarctica?

PETER CLOSE: Well, I would also point out that they’re not just found in Antarctica. Amongst all the many things that are exciting about this group, aside from the pseudo teeth, aside from their giant size, one thing that always strikes me– we, as the scientific community, have found their remains on every major land mass of the planet today.

CHRISTIE TAYLOR: Wow.

PETER CLOSE: This group was existing all over the planet for about 60 million years. To me, that’s a very successful group of organisms.

CHRISTIE TAYLOR: And birds are no longer 20 feet long, or 20 feet wide. Birds no longer have these pseudo teeth that you keep talking about. What happened to them?

PETER CLOSE: We don’t entirely know. As I had mentioned, the youngest known specimens come from that 3 to 2 million year old period. This is a period of time at the end of the Pliocene into the beginning of the Pleistocene. In this 3 to 2 million years, temperatures took a dramatic decline and facilitated the glaciation that we think of when we think of the Pleistocene. the Ice Age, if you will.

So one of our current hypotheses for what happened to these pelegornathids relates to climate change. As these temperatures took a sharp decline, these pelegornathids, however successful they may have been prior to that, couldn’t handle the change, and went extinct.

CHRISTIE TAYLOR: We keep mentioning albatrosses as a size comparison. Are they related to– are albatrosses the descendants of these birds? Or is there another modern bird that they might have left their genetic remnants in?

PETER CLOSE: That’s a very complicated question to answer. Originally, based entirely off of the shape of their bones, it was thought that pelegornathids were related to albatrosses and even pelicans, other soaring birds, birds that travel long distances. But in the last couple of decades, with more specimens being revealed, more specimens being studied, our current hypotheses are placing them, in fact, closer to ducks if you would believe that.

CHRISTIE TAYLOR: What?

PETER CLOSE: [LAUGHS] So this group didn’t begat ducks, but ducks are considered, potentially, one of their closest relatives.

CHRISTIE TAYLOR: OK.

PETER CLOSE: There are some other hypotheses. They may be related to the group that includes ducks and chickens. But that’s currently where our thinking is.

CHRISTIE TAYLOR: Somehow 20-foot wingspan toothed chicken doesn’t quite have the same ring for me as albatross.

PETER CLOSE: Well, as these birds are found in marine and nearshore sediments, places you don’t necessarily see chickens today, it makes more sense to draw the analogy to albatrosses because albatrosses are seabirds. These pelegornathids definitely would have been seabirds as well.

CHRISTIE TAYLOR: All right. So we have these questions still about what happened to them. What is the fossil that’s going to give us the answer?

PETER CLOSE: Skeletons, most certainly are valuable. And with pelegornathids, these are birds. And if you think about birds, you may have heard that they tend to have hollow bones. The preservation of them tends to be a little spotty.

That’s why, with the Antarctic material that my colleagues and I worked on– that’s why we’re dealing with a fragment of the jaw and a fragment of the foot. Finding entirely intact specimens is incredibly rare, but they do exist. There’s one from South Carolina that I’m thinking of. There’s one from here in California. Chile is another place another great specimen comes from. So they do exist.

But to be honest, to answer that question of where’s the next great pelegornathid discovery and is it going to be a skeleton or a fragment, the sky’s the limit. It could go either way.

CHRISTIE TAYLOR: I see what you did there. This is such an excellent mystery, Peter. And I just love this visualization of these birds. Good luck finding more birds in your future. And happy new year, Peter.

PETER CLOSE: Thank you very much. And have a happy new year as well.

CHRISTIE TAYLOR: Peter Close is a PhD candidate in integrative biology at the University of California Berkeley. He’s also at the Museum of Paleontology there. For Science Friday, I’m Christie Taylor.

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