In this episode, you’ll hear about:

• Why Archaeopteryx had half the features of a modern bird and lacked the other half, and what that tells us about 150 million years of evolution

• The "Wonderchicken," a tiny fossil from the border of Belgium and the Netherlands that rewrote what we know about birds surviving the asteroid impact

• How micro CT scanning lets scientists digitally peer inside rocks to study fossils at micron scale without ever touching them

• 00:04 - The Quirks of Paleontology

• 01:09 - The Evolution of Birds: From Dinosaurs to Modern Species

• 09:10 - The Evolutionary Journey of Birds

• 11:59 - The Fascinating Link Between Fossils and Modern Birds

• 26:03 - Advancements in Paleontological Tools

• 27:59 - The Evolutionary Definition of Birds

Timestamp Disclosure
These timestamps were generated using AI and may contain errors or omissions. They are provided for accessibility and reference purposes only and may not perfectly reflect the original audio.

Dr. Daniel Field (Excerpt)

I mean, I'm a weird paleontologist in the sense that. Let me back up. Most paleontologists are pretty weird.

Dr. Scott Taylor

I think most paleontologists, most biologists are weird.

———

You're going to want to share today's episode with a friend who loves birds and the to be birder in your life who may be into things of the Jurassic variety. So buckle up. Birds are familiar. Most of us see them every day of our lives. From pigeons to robins to geese and generally birds look.

Well, they look like birds. And by that I mean birds generally have a similar body. Two wings, feathers, a beak without teeth, skinny scaled legs.

If I asked you to draw a bird without looking at a bird, I bet you could do a pretty good job. It's less this way for mammals. Think dolphin versus bat versus horse. All mammals, but with very different body shapes.

And maybe because birds tend to look like birds and because they're with us wherever you live, on every continent, maybe you've never wondered about their evolutionary history. How did birds evolve and what have we learned from fossils about the evolution of birds? Have you ever seen a baby bird though?

Maybe a chicken or a goose, one that has less feathers so you can get a really good look at how long their legs are. If not, look up a cassowary. C A S S O W A R Y if you're watching this episode, here it is.

Your first reaction might be that really looks like a dinosaur. Or more broadly, have you ever thought, what is a bird? If so, then today's episode is for you. Today we're asking, okay, but what makes a bird a bird?

And to figure this out we'll talk with Dr. Daniel Field, professor of Vertebrate paleontology and curator of ornithology at Cambridge University. Yes, paleontology. Birds have a more complicated evolutionary history than many folks appreciate.

The first time I remember thinking, huh, that looks less like a bird than it looks like a mini dinosaur was. When I was, I think four years old, I was standing in our garage making a little home for salamanders in a jar.

My dad called for me and my brother to come over. He had something cool to show us and I was shocked by what he had in his hands.

I didn't know what species it was at the time, but I knew it was a very, very weird looking baby bird. It was a chunky boy, about the size of an adult robin, maybe a bit bigger, covered in down, but somehow very reptilian looking.

It had a long bill and bright yellow eyes and it looked like half of its Body was legs, legs. For days. You could see how small its wings were because they didn't have their adult feathers yet, and the noises it made.

I felt like one of my tiny little plastic dinosaurs had somehow come to life and was sitting in my father's gloved hands. What is that? My dad didn't know for sure back then, but it would be an easy idea for him now, as an avid birder. A heron, certainly, but what species?

Eventually we figured out that in my dad's hands was a pretty young green heron, which made total sense. We often had green herons hunting along the shoreline by our house. And eventually, years later, we found a nesting pair.

The cool thing about our understanding of the evolution of birds is that we're still learning so much.

New fossils are helping us understand when modern birds first evolved on the planet where they occurred, and how that relates to the mass extinction event that wiped the dinosaurs off the face of the earth just over 66 million years ago. New technology is letting us peer into rocks and characterize fossils in a way not possible even 20 years ago.

Today we'll talk with one of the leading experts in avian paleontology and another fellow Canadian, Dr. Daniel Field, to dive into the fascinating evolutionary history of birds and bird like dinosaurs. And we'll give you a definitive answer to the question, okay, but what makes a bird a bird? Stay tuned. Well, welcome back, everyone.

I'm super excited to be joined by Daniel today. Thanks for joining us, Daniel.

Dr. Daniel Field

Thanks, Scott. I'm really excited to be here.

Dr. Scott Taylor

At the end of every episode of the podcast, I say birds are dinosaurs. And I'd like you to weigh in on what's accurate and misleading about that statement.

Dr. Daniel Field

I don't think there's anything misleading about it. I think it's factually and definitionally accurate. Birds are dinosaurs. Perfect.

In exactly the same way as humans are primates and primates are mammals. So birds are a group of organisms that are nested within a broader group of organisms.

And that's always the case when we talk about any group of organisms on the planet. The organization of life is always hierarchical. And so birds are dinosaurs. They evolved from within this group of organisms that we call dinosaurs.

Dr. Scott Taylor

Perfect.

Well, I guess let's go pretty far back, but, you know, not that far back to the discovery of archaeopteryx, because prior to discovering Archaeopteryx, our kind of understanding was maybe quite different than it is now. So why was the discovery of archaeopteryx so exciting? And let's start there. Why was it exciting? And then we can move forward from that.

Dr. Daniel Field

Yeah, I think Archaeopteryx is sort of an amazing story because it's very important both scientifically and in its kind of historical context.

So the first skeleton of Archaeopteryx, which is actually on display at the Natural History Museum in London not too far from here, is, I mean, it's an amazing fossil, it's a nearly complete specimen and it was discovered in 1861. And so the historical context is kind of amazing because that's only two years after Charles Darwin published On the Origin of Species.

And so the world was really sort of primed for the discovery of an amazing fossil like that one, which combined features that previously were only really known in very distantly related groups of organisms.

And what's kind of amazing about Archaeopteryx is that even today, you know, Getting close to 200 years later, Archaeopteryx remains a really important fossil organism informing our understanding of how the very dinosaur y ancestors of birds evolved into much more birdy descendants.

And so even though it was discovered so long ago and was really the first bird like animal from the age of dinosaurs that had been discovered, it remains a really important, very early representative of a truly bird like dinosaur that helps us understand how and when the features that we associate with birds today first evolve.

Dr. Scott Taylor

Talk a little bit about those features we associate with birds and their evolution.

And I mean, we learned a bit from Archaeopteryx because like you said, it's, there were fossil evidence of feathers for the first time on something that had all these other reptile like characters, those

Dr. Daniel Field

might be things like feathers, the ability to fly, a relatively large brain, a toothless beak, warm bloodedness, a hollow skeleton, just to name a few. And Archaeopteryx is such a cool animal because it basically has maybe half of those features and lacks the other half.

And so it's positioned at a fascinating point in the evolutionary ancestry of birds because it captures a very early stage in the evolutionary history of the bird lineage after the point that things like feathers and presumably at least an incipient ability to fly had evolved.

But prior to things like the loss of teeth, prior to the acquisition of a really large brain, and prior to the acquisition of an extensively pneumatized skeleton that is a skeleton that is really full of air. I do think that it probably was warm blooded, though. I think its physiology probably wasn't too different from what you'd see in living birds today.

Dr. Scott Taylor

Yeah, and there's even just like recent work still trying to understand like, how well could Archaeopteryx fly? Like, was it a. Was it a flap sometimes, then glide, or a powered flyer?

And I think it's interesting that we can get information like that from fossils, but also, like you said, more than almost 200 years later, we're still trying to figure that out.

Dr. Daniel Field

Yeah. It's worth noting that Archaeopteryx is truly ancient. Right. Archaeopteryx lived about 150 million years ago.

And there are some arguments regarding exactly when in the history of our planet the modern bird group first evolved. That is the group defined by the most recent common ancestor of an ostrich and a sparrow, and all of that ancestor is descendants.

But for my money, that group is probably in the range of maybe 100, maybe 90 million years ago, something like that. So Archaeopteryx would have been an ancient fossil even by the time the very first modern birds evolved.

And so understanding really detailed aspects of its biology, like how good a flyer was it? Actually, those are really difficult questions to constrain in a really scientifically rigorous way.

So to me, it makes sense that that sort of remains a slightly open question. Exactly how did it fly and how good was it?

Dr. Scott Taylor

Totally. It's fascinating. So since the discovery of Archaeopteryx, then how has our understanding of modern birds changed?

Because even in the last few decades, there's been the discovery of all of these other fossils that have really informed our understanding. Can you talk to us a little bit about that?

Dr. Daniel Field

Yeah, absolutely. So it's worth kind of thinking about bird evolutionary history in kind of two stages. Right.

There's everything leading up to the origin of modern birds themselves. So Archaeopteryx, of course, is outside of modern bird diversity.

It helps us understand how and when some of those features that we associate with all birds today evolved.

But it doesn't tell us anything about how kiwi became flightless, for instance, or how hummingbirds evolved really long bills specialized for drinking nectar.

To answer those sorts of questions, you need much more recent fossils, fossils that are evolutionarily much more closely related to those extant living bird lineages.

And so our understanding of the fossil record from the age of dinosaurs that helps us understand the transition from dinosaur like animals to bird like animals has improved vastly since 1861.

So has our understanding of much more recent fossils that have revealed how and when and where the incredible diversity of major modern bird groups has evolved. And so I sort of think about those kinds of fossils in different ways because they are suited to answering different evolutionary questions.

But as a Bird paleontologist. I'm fascinated by both of them, these really ancient fossils that help us understand how bird like biology first evolved.

And then those fossils that can tell us, for instance, when did this group become restricted to north and South America, when we know from the fossil record that it previously occurred, let's say, in Eurasia. Yeah.

Dr. Scott Taylor

The discovery of some of those fossils that really clearly show us that birds were diversifying before the asteroid hit the Earth. Because for a long time, this idea out there was that dinosaurs dominated the planet.

Asteroid hit the Earth, they all went extinct, and then there was ecological space for birds to diversify into what they are now. But that's not exactly the story. Right.

Dr. Daniel Field

I think that's a really important element of the story. And I'll caveat that by saying that it remains controversial. This is still area of research. But you're right.

Trying to understand how modern birds and the major lineages of modern birds specifically diversified, to me, that is the absolute most fascinating question in evolutionary biology. And that is why I do.

Dr. Scott Taylor

Unbiased opinion. Yeah, exactly.

Dr. Daniel Field

I love thinking about that. So, I mean, I'm a weird paleontologist in the sense that. Let me back up. Most paleontologists are pretty weird.

I think most biologists are weird, But I'm a weird paleontologist because my interest in fossils, I've always been interested in fossils, but I've also been interested in modern birds for a long time.

And it was right around the time that I was finishing up my undergrad that I became fascinated by this idea that maybe these two interests could actually be linked, that we could use fossils to better understand why birds are so amazing in the present day. And so that's really what motivated me then, and it's still what motivates me now at this point in my career.

And the question that has kind of been front and center for me since I started my PhD a while ago now is how did this diversification event actually happen? Was it a very rapid diversification? When in the history of our planet did it actually happen?

What sort of evidence can we gather to test alternative hypotheses regarding the timing and pace of that diversification from the fossil record? Those are questions that remain really, really interesting to me because fossil evidence of that process is scarce.

It was scarce when I started, and it remains pretty scarce, although we've found some important fossils that have cast new light on that process.

So my opinion is that the diversification of the major groups of birds was largely a very rapid thing, and it largely took place in the Aftermath of this amazing mass extinction event, which took place 66.02 million years ago. We can say that very precisely thanks to good radioisotopic dating of the impact layer.

It's essentially within 10 million years of that impact event that what we think of today as the orders of birds, the 40 plus major groups of birds that encompass all 11,000 living species, first appeared. There's been a lot of effort to find bird remains from the age of dinosaurs.

And indeed, we found tons of fossil bird like animals from the age of dinosaurs, beginning with Archaeopteryx in 1861. But since then, there have been thousands and thousands of fossil bird like animals discovered from the age of dinosaurs.

The issue is that almost all of them are outside the modern bird group. And so they don't bear on this question of when the major lineages of birds diversified.

There are only a very small handful of bird fossils that actually do very clearly appear to be within the modern bird group from the age of dinosaurs.

And those fossils are from the very, very end of the age of dinosaurs, like less than 67 million years ago, when the asteroid hit 66.02 million years ago. So it's really maddening. We know that there was early modern bird fossils right at the end of the age of dinosaurs.

But no matter how hard we've looked at this point, sort of pushing clear evidence of modern birds past about 67 million years, that evidence is just lacking at the moment.

And some of that early evidence of modern birds from the age of dinosaurs is really interesting and I think telling because of the particular groups of birds that those fossils belong to. So, for instance, a few years ago, we named a new fossil bird from about 66.7 million years ago.

This bird came from the border of Belgium and the Netherlands, and we named it Asteriornis. And so this fossil, Asteriornis is interesting because it's clearly a member of the, the modern bird group.

And it seems to be pretty clear which group of birds it belongs to. It seems like an early relative of the group that today includes chickens and their relatives, and ducks and their relatives.

And one of the really interesting things about that group, lots of interesting things about that group, but one of the really interesting things about that group is that collectively the duck and chicken group we call Gallo and Serique, that is one of the three, four, five very deepest lineages of modern birds in the world. We've got this very clear evidence of a modern bird from the age of dinosaurs, even though it's just barely from the age of dinosaurs.

But it belongs to one of those very, very deep lineages of birds that pretty uncontroversially before its discovery, we thought probably would have been around prior to the asteroid impact. What we don't have is any evidence from this huge group of birds that we collectively call Neoavians, which represents over 10,000 living species.

This is the group that includes hummingbirds, passerines, and almost any other bird that you can name that isn't a galoanserran. So a duck relative or a chick relative, a chicken relative or a paleonth, an ostrich relative.

So as far as we can tell, it seems like the massive diversification of this group, Neoavies, seems to have been a post asteroid phenomenon.

And so I think this hypothesis that you mentioned, that the ecological space that opened up after the asteroid impact eliminated all non avian dinosaurs and so many other things, facilitating the rapid diversification of birds in the asteroids aftermath. I think that hypothesis is still valid. And indeed I think as time goes on, that hypothesis becomes stronger and stronger.

Dr. Scott Taylor

Did you guys come up with the name Wonderchicken or was that the press?

Dr. Daniel Field

I think I probably did. I think I was thinking of the old Simpsons episode where Homer gets a wonder bat and he hits tons of it was pretty deeply intellectual

Dr. Scott Taylor

as these things are.

Dr. Daniel Field

Asteriornis took a little bit more thought. So that name was proposed by my co author and really good friend Dan Sepka, who's a world expert in fossil penguins, among other things.

And so that name comes from the Greek goddess Asteria, who was the Titan goddess of falling stars. And so that seemed apropos because Asteriornis is from so close in time to the asteroid impact.

And there were a few other reasons, kind of cute reasons that made Asteria an appropriate namesake for this fossil, including the fact that she supposedly transformed herself into a quail. And of course quails are Galloanserans, being close relatives of chickens and other pheasant like birds.

Dr. Scott Taylor

Yeah, no, that's fascinating. I mean it must have been so exciting.

And that got a lot of attention obviously, because it did, like you say, placed at least one of these lineages of modern birds pretty solidly as existing prior to the impact of the asteroids.

But yeah, for people listening, in terms of modern bird diversity, there's yeah, about 11,000 extant species, depending on how you describe a species. And over 6,000 of those are one group, the passerines, which are the perching and singing birds.

Dr. Daniel Field

But I will say the really cool thing about basically all of those groups of Neoavies is that by 10, 15 million years after the asteroid impact, we've got direct fossil evidence of almost all of them. And so that's the really clear fossil story here.

These groups do seem to appear relatively abruptly in the fossil record after the impact, but there's simply no evidence of them in the fossil record before the impact, despite the fact that we have all of those thousands and thousands of sort of dino bird fossil groups from before the impact.

And so I think the fossil evidence that this group, Neoavies, which of course includes passerines, arose after the end Cretaceous mass extinction event. My opinion is that that hypothesis is a very strong one.

Dr. Scott Taylor

Well, and that's why we're talking to you, to get the take on how all of these birds diversified and when they occurred. The fossil record is interesting and it might be.

I think people would be interested in hearing about what conditions are required for a good fossil to form. And obviously it's variable. But the reason that the fossil. I mean, one of the. I'm not a paleontologist. We know that.

But the fossil record is incomplete in part because it depends on where you die. Right. And the conditions after death to create a fossil. Can you tell us a little bit about that?

Dr. Daniel Field

The bird fossil record is extra annoying.

Being a bird paleontologist is just the most insane decision to make, because the bird fossil record is much poorer than the fossil record of most other groups of vertebrate animals, simply because birds bodies are relatively lightweight and their skeletons tend to be pretty fragile.

So my friends who study fossil turtles have it so easy because basically turtles are essentially living rocks, and so they preserve well in the fossil record. And when I've gone out looking for bird fossils, I found very few bird fossils in the field in my life, but I found a lot of fossil turtles.

The other annoying thing about modern birds is that very frustratingly, they lost their teeth. And so teeth fossilize really well because they're so hard.

Enamel preserves extremely well in the fossil record, but as soon as teeth have been lost, evolutionarily, the ability for those very hard tissues to get preserved disappears. So bird skeletons are relatively scarce in the fossil record compared to other groups.

But as I've already mentioned, there are thousands and thousands of important bird fossils out there that we're able to study. So I guess I can't complain too much.

Dr. Scott Taylor

You have a job.

Dr. Daniel Field

Yeah, that's true. Now, the bird fossil record is more tied to sort of special preservational conditions than the fossil record of other groups of vertebrate animals.

Just because it's so difficult to preserve birds in the fossil record. So remains of very slow moving bodies of water that had relatively high sedimentation rates.

Those are the sorts of paleoenvironments that tend to preserve bird fossils better than other environments.

The fossil record of birds from about let's say 50 to 55 million years ago is pretty amazing because of this chance occurrence that there are a number of fossil deposits that were formed in those sorts of environmental conditions all around the world. And therefore we've got this beautiful snapshot of fossil birds from between, about, well, let's say 48 and about 53 million years ago.

And that, of course, is a really interesting interval in the history of our planet. We're less than 20 million years after the asteroid impact.

So those localities provide us with some of the best early snapshots of sort of very early representatives of major modern bird groups. And so some of those really amazing localities are in North America. In fact, I know you're based in Colorado.

One of the most famous of all of these localities does sort of crop out in Colorado.

And there are other sort of roughly contemporaneous fossil localities still, including one here in England, not too far away from where I am, that crops out on the coast of southeast England called the London Clay Formation and the London Clay preserves.

It's about 53 million years old, which places it just after an extremely warm interval in the history of our planet, the Paleocene Eocene thermal maximum.

And it's that locality that has produced early representatives of groups that we think of as tropical in the present day, but whose distributions extended to very high latitudes around 53 million years ago, because the Earth was much warmer then. And that includes things like troguns.

Dr. Scott Taylor

Yeah. The Trogan example is one I use in class. I show them the contemporary distribution and I ask how did they do this?

They couldn't fly across oceans, and it takes them a while, but eventually they think about the fact that the Earth was warmer before and that these more contiguous tropical rainforests, which are kind of trogun habitat, were, were more connected at that time.

Dr. Daniel Field

Yeah, troguns are good to think about. A neat example, right. Because they're pantropical. Right.

You've got them at kind of equatorial latitudes and sort of flanking those equatorial latitudes all around the world.

But when those sorts of warm, wet conditions associated with what we would think of today as tropical forests extended up to the sorts of latitudes where you and I grew up. Yeah, I mean, that's Trogan habitat, baby.

Dr. Scott Taylor

Yeah, for sure. We haven't shout out, given Canada a shout out yet, so I appreciate you pointing that out, I think. I don't know if people can hear it in my voice.

I can hear it in your voice, though. You still sound Canadian.

Dr. Daniel Field

Yeah, I know it faded because I did my PhD in the US, but. Yeah, I don't know. Especially when I talk to my friends from Canada. I know my accent let it out.

Dr. Scott Taylor

Like you said, you started your PhD in 2010. How have the tools that are available to use to ask questions changed? I don't know.

I hear a lot about, you know, micro CT scanning and things and imaging in ways that instead of chipping a fossil out of the rock and then putting it back together, you can actually look at it while it's still there. Can you talk just a little bit about that?

Dr. Daniel Field

Yeah, of course. So.

So those sorts of tools that allow us to interpret anatomy more precisely at higher resolution have been actually revolutionary for the field of vertebrate paleontology. So, for instance, with this fossil, Asteriornis, you mentioned the Wonderchicken. That fossil is teeny tiny, very delicate.

The skull itself is, like, less than 7cm long.

And so had we tried to chip that fossil out of the rock that surrounds it, we probably would have damaged it and in the process, obliterated some of the most important fossil evidence that exists of birds from before the asteroid impact at the end of the age of dinosaurs.

So, fortunately, we were able to take the little rock that surrounds the skull, put it in a very high resolution, very powerful micro CT scanner that we have in the basement of the Museum of Zoology here in Cambridge, and thereby digitally peer inside the rock and at micron scale, observe the very detailed osteology of that skull. So that's an amazing thing.

It's something that not very many people were doing in 2010, but by 2026, early 2026, when we're having this discussion, that has become a standard approach in the field of vertebrate paleontology, and for good reason.

Dr. Scott Taylor

Yeah, it's amazing to look at the visualizations of Those and these 3D models you can generate and spin around on your computer. And I just can't imagine zooming back in time to some of the first paleontologists and being like, look what we can do now.

Their heads would have exploded with excitement, I think. So if someone walks up to you and asks, what is a bird? What do you tell them?

Dr. Daniel Field

I can get pedantic about that because it can be a tricky question to answer, but I think there's only One kind of objectively accurate way to answer that question. So for me, when I think of birds, I think of modern birds or the bird crown group as a natural group of organisms that we can define.

We can define it as the most recent common ancestor of an ostrich and a sparrow and all of that ancestor's descendants.

So that definition encompasses, of course, all 11,000 plus living species of birds, but also all of that extinct diversity, like those early hummingbirds from Europe that we were talking about, those early Croghans from the London Clay and Asteriornis too, going back to the most recent common ancestor of all living birds.

And of course, that definition excludes most of what we know of from the Mesozoic fossil record, the age of dinosaurs, including Archaeopteryx, but including all of these other sort of premodern birds.

And I think that is okay because we can define the relationship of birds to those earlier organisms also with respect to how these things are related evolutionarily. And really, I think that's the only way to do it. And the reason that we can't just say that a bird is anything with feathers is because.

Which would be easy and nice and I guess, true, except evolution happens. Right.

And so paleontologists tend to balk at the idea of defining groups with respect to features that they share, because over really long periods of time, we know that those features change. The only sort of uniformly, I think, accurate way to define groups of organisms is with respect to evolutionary relationships.

Dr. Scott Taylor

Well, we're on the same page there.

Dr. Daniel Field

Agreed.

Dr. Scott Taylor

So we reached the part of the show that we call that's BS or that's bird stuff, where we give our guests an opportunity to debunk a myth that ruffles their feathers. So, Daniel, what do you want to call BS on?

Dr. Daniel Field

What I think is sort of BS is this assumption that as time goes on, we'll find early representatives of many, many major groups of modern birds.

Things like early hummingbirds, things like early passerines, things like early parrots, which I think almost certainly did not exist during the age of dinosaurs, because we have such an extensive fossil record of bird like forms now from before the asteroid impact, with no evidence for any of these groups of neoavian birds yet, no really compelling evidence. Whereas after the extinction event, all of a sudden we've got early representatives of virtually all of these major groups of modern birds.

So a strict reading of the fossil record is not called for.

Obviously, we have to draw some inferences about exactly when, before and after the mass extinction event, aspects of Modern bird diversification took place, but the signal seems to be really, really strong that there was a massive diversification of the major groups of neoavian bir the mass extinction event. And I will say all of what I've just articulated, of course, is testable.

So if an early owl or an early ostrich or an early kingfisher or something like that turns up in rocks that are 100 million years old, well, I'll shut up.

Right, because we can reject my little hypothesis here, but I simply don't think that's going to be the case, given how many fossils have turned up from both before and after the asteroid impact that just haven't suggested that neoavian birds had diversified much before the mass extinction event. So I just think that is bird stuff, Scott.

Dr. Scott Taylor

It's definitely bird stuff.

I'm going to go back to my early birds lectures and just tweak them to make sure I'm in line so that these Canadians are aligned across the pond with how we teach gratitude. Awesome. Well, thanks so much for joining us today. This has been an awesome conversation, as I knew it would be. And it's good to see you.

Dr. Daniel Field

Yeah, thank you, Scott. I'm so excited to have. I've been invited to join the podcast. I love the podcast. And yeah, I can't wait to see this up online on Spotify.

Dr. Scott Taylor

Birds are dinosaurs. And around here we like our snacks. So we end each episode with a dinosaur nugget. Today we could just leave it there. Microphone drop.

But really, birds are dinosaurs. And although some modern bird lineages do predate the mass extinction event that caused the extinction of non avian dinosaurs.

Remember the Wonderchicken? Many lineages of modern birds first appear in the fossil record around 10 million years later.

Oh, and trogons and hummingbirds used to fly around Europe. That's a wrap on this week's episode. Okay, but what makes a bird a bird?

If you liked it, make sure to leave a comment like and subscribe and share this with a friend. We'll catch you next time. Byeee. Okay, But... Birds is hosted by Scott Taylor with production and creative by Zach Karl.

Transcript Disclosure
This transcript was generated using AI-assisted transcription and may contain errors or omissions. Please refer to the audio or video episode for the most accurate representation.

All audio, video, and images in this episode are either original to Okay, But... Birds (© Okay Media, LLC) or used under license/permission from the respective rights holders. Bird media from the Macaulay Library is used courtesy of the Cornell Lab of Ornithology as follows:

• Great Spotted Kiwi, William V. Ward, ML810

• Southern Cassowary, Linda Macaulay, ML57219

• Elegant Trogon, David L. Ross, Jr., ML199536

• Green Heron,, Bob McGuire, ML229117

Asteriornis imagery and video courtesy of Dr. Daniel Field, University of Cambridge.