The word 'dinosaur' refers to a specific group of animals. Many animals get included under the dinosaur umbrella when they are actually from different groups. Becca from our programs team helps us set the fossil record straight.

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ERIC: From the Museum of Science in Boston, this is Pulsar, a podcast where we dig around for answers to the most technically accurate questions we've ever gotten from our visitors. I'm your host, Eric, and I am one of many educators at the Museum of Science who are fascinated by ancient life. A group of animals called the dinosaurs dominated the planet Earth for hundreds of millions of years. And some extinct animals are included under the umbrella term of 'dinosaur' when they are actually something else entirely. Here to help me sort out the dinos from the di-nots is Becca from our Museum Programs team. Becca, thanks for coming back on the podcast. And I know you're excited to talk about dinosaurs and dinosaur-like animals.

BECCA: I am always excited to talk about dinosaurs.

ERIC: So sometimes I feel like a little bit of a nerd when I see dinosaurs in, like, a kid's book or in a movie. And I'm like, um, technically, that one is not a dinosaur. Do you feel the same way? Are you kind of just like, yeah, we can call all ancient animals 'dinosaurs'?

BECCA: I absolutely feel the same way. And I will actively say it out loud. I own that nerd-ness.

ERIC: So let's start with what a dinosaur is. When someone says, 'Okay, well, what is a dinosaur?' Then what do you usually say?

BECCA: So I generally give a basic definition of dinosaurs were a group of animals that lived from about 220 million years ago to about well, either 65 million years ago, or now, depending on if you classify birds as part of dinosaurs or not. But they were kind of related, if not part of the reptile group. That is where a little bit of science gets a little bit confusing, and something that has been rewritten and reclassified a few times. But there were many other types of reptiles that existed at the same time as them. And now we have many reptiles that have diverged completely from the branch that dinosaurs were, so while the definition is a little bit complicated, we know there are a lot of animals that were not dinosaurs.

ERIC: I think where we should start is one of the most common ones because whenever you see a group of three dinosaurs, I usually see a pterosaur in there. It's like, usually you get something like a T. rex, and a stegosaurus or a triceratops, and a pterosaur. And they are not dinosaurs. They are flying reptiles.

BECCA: Correct. Pterosaurs are not considered to be part of the dinosaur group. They are reptiles and they are flying reptiles.

ERIC: Now when I was younger, it was always pterodactyl. And pterodactyl meant the flying dinosaur, which we just said: it's not a dinosaur, but what's the difference between pterodactyl and pterosaur? Which one is the better one to use?

BECCA: That's a great question. I would definitely be using pterosaur more than pterodactyl because pterodactyl is just one specific species of pterosaur. Pterosaur is any flying reptile. Whereas pterodactyl was one specific type, we also have pteradon, we had the Quetzalcoatlus. There are so many types of flying reptiles that existed during the time of the dinosaurs. But we can call them all pterosaurs.

ERIC: It's so cool, because that's another thing when I was growing up, it was like, okay, there was pterodactyls, which are the flying ones. And, you know, they're always about the same size and about the same color. And the wide variety over those hundreds of millions of years, the tiny little ones, we have a couple of models of those here at the museum. That Quetzalcoatlus like you mentioned, it's the size of a giraffe. I mean, I really wish there was videos, I really wish we could have seen these entirely different kinds of life that we just don't have today.

BECCA: It blows my mind that we had a creature the size of a giraffe that could fly and was also a reptile. I wish we had it around.

ERIC: So something else that's not a dinosaur we still have today are crocodiles and alligators. And we had ancient prehistoric forms. You'll hear someone say, they haven't changed at all, like alligators and crocodiles have just survived all the extinction events. And you could find them all the way back. And I guess in a way that's true, because they haven't changed very much. But there were other versions of them around the same time as the dinosaurs that weren't dinosaurs, like huge, giant ones, right?

BECCA: Absolutely. We had some pretty interesting, different crocodile- and alligator-like creatures. Now they have changed. So they're not exactly the way that they are right now. But they haven't changed nearly as much as many other types of animals out there. So it is definitely right to say that they have stayed at least a little bit similar, but they have changed enough that they wouldn't look like our modern day crocodiles and alligators at all. But again, those were reptiles that existed during the time of the dinosaurs, also not dinosaurs.

ERIC: And another ancient reptile that probably doesn't get confused with dinosaurs too much but the titanoboa, the largest snake to ever exist. 50 feet long. I couldn't wrap my arms around it because it was so thick. That's another one that I really just wish we had more than a couple of backbone fossils from.

BECCA: I know the titanoboa, the largest snake to have ever existed, at least as far as we are aware right now. I mean, think about it. Even now, our modern day boas can't get to be nearly that big. And our biggest snake that we have in the world, the reticulated python, is about 30 feet long. So think of something that is 20 feet longer than that. And the width of it was a lot larger. It was a massive snake, but again, not a dinosaur.

ERIC: Now a lot of the confusion comes up with the ocean, because dinosaurs did not live in the ocean, but there was lots of life in the ocean at the time.

BECCA: We had a lot of interesting creatures in the ocean. Definitely made a little bit more popular from my favorite movie franchise that has come out recently. But we have plesiosaurs, we have mosasaurs, ichthyosaurs, megalodon, we had a lot of stuff going on in the ocean. And you guessed it, they were not dinosaurs. In fact, they were all different ocean creatures. Many of them were ocean reptiles. So the plesiosaurs, mosasaurs, and ichthyosaurs, were aquatic reptiles, whereas the megalodon was a shark. I know, Eric, that is one of your very favorite types of animals in the world.

ERIC: But the megalodon is just so cool. I mean, it's something I always was into growing up. Sharks, anything to do with sharks, and to find out that there was a shark that was many times bigger than any of the sharks that exists today. And it didn't go extinct that long ago, it was still around on the earth up until just a couple million years ago. I mean, we have a couple episodes in this podcast series where I talk to a megalodon expert about what happened to them, but also what they were like in life. And that was just kind of really cool to talk to somebody who researches them for a living. But yeah, they weren't dinosaurs. And they weren't reptiles.

BECCA: Yeah, all of these aquatic creatures were not in fact, dinosaurs. In fact, we didn't have any dinosaurs that spent any time in the ocean. But there is one that could have done a little bit of swimming.

ERIC: So I think you're talking about spinosaurus.

BECCA: Oh, I absolutely am. My favorite dinosaur. spinosaurus is the only semi-aquatic dinosaur that we are aware of. So the only dinosaur that could be on both land and water. Now the biggest problem with spinosaurus, and the reason why I say right now it is my current favorite dinosaur, is that because it may end up being reclassified. The more we find out about it, the more we realize it is not just a T. rex with a sail on its back, we realized that it could swim almost like a crocodile or alligator using that powerful tail to switch back and forth, and that that sail may have been helpful for swimming. The more we find out about it, the more we may think that it is some sort of reptile and no longer part of the dinosaur category. So I will say for now, spinosaurus is my favorite dinosaur. But stay tuned because that one too, may become a separate group of reptiles.

ERIC: I do love that story. Because it's an another example of how science is always moving forward. As we understand more, we're always getting more evidence and painting a clearer picture. And we found spinosaurus fossils 100 years ago, and started to piece them together and understand a little bit and then the best ones got destroyed in World War II. And so it was like, back to the drawing board, where we were like, What is this huge animal and what was it like in life. And just in the last decade that I've been following, you know, new dinosaur discoveries, seeing that there's another one that was found, and then another one that was a little bit more complete. And then the most recent, that its tail actually had that extra little bit that it wasn't like a T. rex tail that just tapers down to nothing, that it actually had a paddle tail, that we might actually have enough to reclassify it. It's crazy.

BECCA: It is pretty amazing. And I'm excited with every single thing that we find out about this creature because the more we find out about it, the more our vision of what this animal was changes, and the more likely, sadly, it will not be considered a dinosaur.

ERIC: Now we said no dinosaurs maybe other than spinosaurus could swim, definitely not in the ocean. Spinosaurus was maybe more in like a lake or river or something. What about flying? Did dinosaurs fly?

BECCA: This is where we start to get into dinosaurs of the present. Now my favorite thing to talk about is that when this massive extinction event happened when the asteroid or meteor hit the earth about 65 million years ago, not everything disappeared. In fact, the smaller dinosaurs, especially those that were the two legged ones, were able to find enough food during this entire impact event that caused droughts and plants to die off and other animals did not find enough food, those smaller two legged animals were able to survive a little bit better. And over many millions of years, they were able to evolve and become modern day birds. Now, Archaeopteryx is one of my favorite examples of this sort of dinosaur-bird hybrid animal that we're not entirely sure where exactly it might fit in. But it had these wing-like structures showing us that it was very likely one of these crossovers as we went from dinosaur to bird and had some of these flying dinosaurs. And now, we're finding dinosaurs everywhere.

ERIC: We're lousy with flying dinosaurs.

BECCA: Yes, so many of them.

ERIC: I want to mention one more that gets lumped in all the time, that's just my favorite because I never knew anything about it. And that is dimetrodon, which also just gets thrown in. You see it in illustrations as being a dinosaur. It's that big lizard-looking thing with the giant sail on its back. But it's much lower to the ground, on all fours, than spinosaurus. And I always just thought, okay, yeah, that's a kind of a dinosaur. And it turns out that it's ancient, it was around way before the dinosaurs even evolved.

BECCA: Yes, the dimetrodon was one of those really interesting creatures that had often been confused, or at least spinosaurus had often been confused with it. But it did exist well before the dinosaurs. In fact, about 40 million years before the first dinosaurs evolved, it was when it went extinct. And based on further evidence, even though it kind of looked more reptile-like in some ways, it's likely more closely related to mammals. In fact, it's part of the same group that mammals eventually ended up being put into, whereas reptiles and dinosaurs, and birds are all in an entirely different group of animals. So dimetrodon, while being kind of reptile-like, kind of spinosaurus-like in many of its aspects, was actually probably more closely related to us. Just really fascinating.

ERIC: I just couldn't believe that when I first read that it was this early mammal-ish, like, I'm closer cousins with the dimetrodon than I am with so many things that are still around today. That's kind of why I don't mind correcting people and saying, "technically, that's not a dinosaur" about all of these things. Because it's not really disappointing. It's just amazing that life looks the way it does. And it's changed so much and is evolved to be similar to each other in so many ways.

BECCA: Absolutely. It's so funny that so many people think of anything ancient anything being several hundreds of millions of years ago as dinosaurs. But in reality, during that time, life was very diverse. There were reptiles, there were amphibians of various sizes, there were small mammals, which eventually got to take over once those dinosaurs left. And there were just so many different types of animals that were out there. And while some of it looks a little bit similar to today, and some of it stayed around and evolved over many millions of years, some of it didn't. And those are the ones that the more we find out about the more we learn more about our past life on our planet.

ERIC: Becca, thanks for telling us all about what's not a dinosaur.

BECCA: Anytime.

ERIC: On your next visit to the Museum of Science, be absolutely sure to stop by our Dinosaur exhibit, Modeling the Mesozoic, and see how well you do at sorting the dinos from the rest. And while you're home, follow the Museum of Science on Instagram to keep up with the latest dinosaur discoveries. Until next time, keep asking questions.

If you liked this episode, be sure to check out:

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Why Did Dinosaurs Have Feathers?

A Shark the Size of a School Bus... What Did It Eat?

What if the Dinosaurs Hadn't Gone Extinct?

Did T. rex Eat Stegosaurus?

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