Remarkably Well-Preserved Archeopteryx Specimen Unveiled

SOPHIE BUSHWICK: This is Science Friday. I’m Sophie Bushwick, senior news editor at New Scientist. I’m filling in for Ira this week. Later in the hour, what causes tinnitus and why treatments could be on the horizon, plus climate change and the future of sports. But first, the Field Museum in Chicago just unveiled a new specimen of one of the most, if not the most, important fossils ever, Archaeopteryx. It lived around 150 million years ago. And this species is famous for marking the transition from dinosaurs to birds in the tree of life.

The Field Museum now has the 13th known fossil, and it may be the best preserved one yet. Joining me to talk about this fossil find and what makes Archaeopteryx so fascinating is Dr. Jingmai O’Connor, associate curator of fossil reptiles at the Field Museum in Chicago. Welcome back to Science Friday.

JINGMAI O’CONNOR: It’s always a pleasure.

SOPHIE BUSHWICK: How exciting is it to have an Archaeopteryx specimen in your museum?

JINGMAI O’CONNOR: Oh, it’s incredibly exciting. I think for any paleontologist, they would be really stoked to have a specimen of Archaeopteryx because it really is the icon of evolution. But my specialty is specifically Mesozoic birds. So for me, it’s just like– I can’t even say a dream come true because I never would have dared to dream something like this. But yeah, it’s amazing.

SOPHIE BUSHWICK: And clearly, you have a lot of enthusiasm for Archaeopteryx. So tell us about it. What did it look like? How did it move? How did it eat?

JINGMAI O’CONNOR: Yeah, so Archaeopteryx was a small bird that ranged in size from about a pigeon to a crow. And in fact, even the largest specimen shows evidence it was actively growing. So we don’t know how big they got. But you would identify it as a bird because it would have been covered in feathers, and it would have had wings.

But it would have had a long reptilian tail. It would have had jaws full of teeth. It would have had claws on its hands. So in this way, it’s the perfect transitional taxon that’s recording these very bird-like characteristics together with reptilian, non-avian, dinosaurian characteristics.

Now, we actually don’t know what it ate. No specimen preserves stomach contents. And whenever we see a species that appears to be carnivorous, but is very small, our default go-to is that it was insectivorous. So that’s what most people hypothesize for Archaeopteryx. But I just want to make it clear that there’s actually no evidence of that.

SOPHIE BUSHWICK: And why is it such an icon of evolution?

JINGMAI O’CONNOR: I mentioned that it’s this transitional taxon, right? And what’s really special about it is that it was found just two years after Darwin published on the origin of species by means of natural selection. So in it, he puts forth his theory for one of the major mechanisms of evolution, that organisms that are better adapted for their environment are more likely to survive and pass on these adaptations that led to their success.

But in the book, he also says, the gravest objection to my theory is that we don’t have fossils that are recording morphological transitions from a species adapted for one environment to a species adapted for a different environment, like, for example, a non-flying theropod dinosaur to a bird. And that’s exactly what Archaeopteryx provided just two years after he published this book.

And this theory needed evidence. It needed support. It was being heatedly debated in the academic and also, religious sectors. So it was just perfect to have this iconic transitional taxon found in just the nick of time to support Darwin’s theory. And for that reason, it’s the icon of evolution.

SOPHIE BUSHWICK: So we know that birds are dinosaurs, but why didn’t they die alongside their ancestors when the asteroid struck?

JINGMAI O’CONNOR: So some birds did die. There were lots of lineages of Cretaceous birds that go extinct alongside non-avian dinosaurs. But crown birds probably survived because of a combination of characteristics. I think you usually can’t point to a single thing and say, this is why this one particular group went extinct.

And it’s probably because crown birds have very high metabolic rates. They had contact incubation, and their eggs could move, which allowed their incubation times to be shorter, which means that the period in which you have to sit on a nest and you’re vulnerable is reduced. We also think that they had a more efficient digestive tract than perhaps other birds and non-avian dinosaurs. So those are the hypotheses that we’re leaning towards, maybe more efficient respiratory system as well. But again, there’s really no strong evidence for all of this. It’s really hypothetical. Basically, we don’t know.

SOPHIE BUSHWICK: Well, let’s get into your particular specimen of Archaeopteryx. How did the Field Museum get its hands on this fossil in the first place?

JINGMAI O’CONNOR: So this fossil has been in private hands, unprepared for over three decades. And the current owner was looking to sell it to another private collector. But this private collector instead told us about the fossil to try to get the fossil into a public repository and make it available for scientists. So yeah, that’s how we were able to acquire it.

And it was a total gamble because it was unprepared. And we could just see a little bit of the specimen. And we really didn’t know what we were getting. And as soon as we got it to the Field Museum, we popped it in the X-ray machine. And it’s so perfectly three-dimensionally preserved, that all the bones are still preserving all their hollow spaces inside. And so hollow spaces in an X-ray show up as black because it’s very– it’s the lowest density, right?

SOPHIE BUSHWICK: Mm-hmm.

JINGMAI O’CONNOR: And the whole skeleton just popped on the screen in black when we X-rayed it.

SOPHIE BUSHWICK: Oh, wow.

JINGMAI O’CONNOR: And it was just so, so exciting. And also, we’re a scientific institution that’s prioritizing the scientific value of the specimen and not just its beauty, which is what is more valued by private collectors. So we really meticulously prepared this. Or I didn’t. It was Akiko Shinya and Connie Van Beek. 1,270 hours of fossil prep have led us–

SOPHIE BUSHWICK: Oh my gosh.

JINGMAI O’CONNOR: –really having a very strong argument for this being one of the best Archaeopteryx, without a doubt one of the best, if not the best.

SOPHIE BUSHWICK: What makes it the best?

JINGMAI O’CONNOR: I would say it’s the best because it’s almost 100% complete, just missing the tip of one of the fingers. It’s uncrushed, so we get the three-dimensional morphology of the bones. A lot of other specimens are crushed. We also have extensive soft tissues, including soft tissues that have never been seen before. The scales that form the foot pads on the toes, that’s also articulated. So all the bones are where they would be in place.

And we also are spinning one negative to our advantage. So there are small counter slabs that we could have united with the main slab during fossil prep. But we chose not to. And this is because this is opening the array of analyzes that we can do when you have a small sample.

For example, you can’t take this giant slab and stick it inside the chamber of a scanning electron microscope. But these little, small counter slabs that we have, you definitely can. You can. And so there’s all sorts of cool analyses that we have planned for the future that are not possible to do on large slabs and basically, all the other previously known specimens.

SOPHIE BUSHWICK: So what can you specifically learn from this one that you wouldn’t have been able to learn from the others, the other 12 known Archaeopteryx specimens?

JINGMAI O’CONNOR: So there’s a lot of chemical analyses that we’re going to do that would be very hard to do on a very large specimen. But actually, we’re learning just a ton of basic new information. I thought Archaeopteryx– there’s 12 specimens. The first one was described 163 years ago. I didn’t expect that we were going to learn a lot of basic anatomical information.

But actually, we’re actually redefining some pretty important aspects of the skeleton, like just what the skull looked like, what the palate looked like. We have the first-ever complete vertebral column. We can show lots of different bones looked slightly differently than previously thought.

And this might not sound that important, but if you really want to understand the relationship of Archaeopteryx and other birds to non-avian dinosaurs, you really need to know, have an accurate understanding of, the skeletal anatomy. And that’s what this fossil is giving us.

SOPHIE BUSHWICK: And like you mentioned, this is the 13th fossil. But do you still want more Archaeopteryx fossils? What more can you learn from additional ones, you think?

JINGMAI O’CONNOR: Well, oh, I hate to sound greedy, but yes, I absolutely would love more.

[LAUGHTER]

I mean, there’s still so many questions that we don’t know. We don’t understand if they all represent a single species. This is something that’s very heatedly debated. Every specimen at some point has been considered to be a different species. So I don’t know what that says about our 13th, if at some point, somebody is going to claim it’s a new species.

But we also don’t understand what the size variation in these animals mean. Does it represent a growth series? Or are we looking at evidence of developmental plasticity? Was there a sexual dimorphism? there are a lot of questions that you need a significant sample size to address, and more would always be better.

SOPHIE BUSHWICK: And you talked about how you can distinguish you know how many vertebra it had and how its skull palate is shaped. But why are those things important to know? What difference do they make?

JINGMAI O’CONNOR: So if you want to understand the relationship of Archaeopteryx to non-avian dinosaurs, the only way for us to do this is to compare the shape of the bones. And so for us to be able to accurately compare Archaeopteryx to the closest non-avian dinosaurs, we need to accurately know what it looked like. So for example, we’re drastically changing what the skull looks like, and it actually looks more Troodontid-like.

And it’s a hypothesis that I’ve had for a long time. I’m not alone in this, that birds may be a group of Troodontid dinosaurs. So we could not even say that birds are living dinosaurs. We can say birds are living Troodontid dinosaurs. I mean, this is still a hypothesis, but this is what this new information is strongly suggesting. And so I think that’s really exciting, to be able to give evidence for one of the most important research questions for somebody who works on Theropod dinosaurs and works on birds, is where birds fit in the dinosaurian tree.

SOPHIE BUSHWICK: And, Jingmai, before we go, I want to know what other fossil is on your dinosaur shopping list. What remains would you love to get your hands on?

JINGMAI O’CONNOR: Oh, goodness, that’s a great question. I don’t necessarily want them in my own institution. I just think it’s wonderful to have fossils available for scientists around the world. But I guess what I would like are– this is going to sound so boring and nerdy. I want more late Cretaceous birds.

So we actually have a very good sampling of the earlier part of avian evolution, mostly thanks to these early Cretaceous fossils from China. But we know very, very little about birds in the late Cretaceous. And so this all important question, why do crown birds survive the end-Cretaceous mass extinction? we need late Cretaceous bird fossils to really answer that question. And so that’s actually what I’ll be going out this summer, spending a month in the field looking for.

SOPHIE BUSHWICK: What did those Cretaceous birds look like?

JINGMAI O’CONNOR: Birds are incredibly diverse now. There’s a total range of shapes and sizes. And the same absolutely would have been true for birds in the late Cretaceous. We have birds like Hesperornis, which was a very large, but flightless bird, almost completely reduced its wings. It would have lived in the oceans and used its feet for swimming and paddling.

There would have been tooth birds in the latest Cretaceous. There would have been birds with beaks. There would have been birds the size of hummingbirds. There would have been birds the size of turkey vultures, raptorial birds, arboreal birds, very, very similar today except for the presence of teeth in some of them. I suppose.

SOPHIE BUSHWICK: I clearly– I need to appreciate birds more, both the ones we have now and their distant ancestors.

JINGMAI O’CONNOR: Definitely. I think thinking about them as dinosaurs– next time you see a bird and look at that pigeon on the street and say, that’s a dinosaur. And then suddenly, notice the way it moves, the way its neck moves. And then think of that as a dinosaur. And then think about things like Deinonychus moving like that. And I don’t know. It’s pretty exciting and fun to think about it. And hopefully, it will give you a greater appreciation for the dinosaurs alive today.

SOPHIE BUSHWICK: Definitely. Dr. Jingmai O’Connor is associate curator of fossil reptiles at the Field Museum in Chicago Thank you so much for sharing your knowledge with us.

JINGMAI O’CONNOR: Oh, my pleasure. Thank you for having me.

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