(SciShow kids intro plays)

Jessi: Oh hey guys, we invited a friend over to hang out today. He's a lot of fun! His name is Dino and he loves dinosaurs. He has all kinds of dinosaur costumes.

Dino: It's true, dinosaurs are so cool!

Jessi: and who are you wearing today, Dino?

Dino: T-rex! My favorite dinosaur right now is actually the Ankylosaurus, but they had four legs so that costume is kinda awkward. Plus, I got grape juice on it, so my dad has to wash it.

Jessi: Well I think you look great! You might already have guessed this, but Dino knows all sorts of things about dinosaurs.

Dino: I love reading about them. I've read all the books about them in the library.

Jessi: Well, why don't you tell us a little bit about what you've learned so far? Maybe you can start with this: what makes a dinosaur a dinosaur?

Dino: Hey, good question, Jessi. There were all kinds of dinosaurs that lived millions of years ago. Some had two legs like T-rex here, and some had four legs like Ankylosaurus, some ate plants and some ate other animals, but they all had a few things in common.

Jessi: Like what?

Dino: Well, one way to tell whether an animal's really a dinosaur or not is to look at its legs.

Jessi: Its legs? really?

Dino: Yeah, let me show you. First, have a look at this guy, it's a Komodo dragon. It's the biggest lizard in the world today. It lives on some islands in Asia, but Komodo here isn't really a dragon, it's a reptile. It has scaly skin and a long tail and I can totally see how some people might think it looks kind of like a dinosaur, but look at its legs. Its legs stick out from the sides of its body, so the feet are on the sides, too, almost like it's doin push-ups.

Jessi: Oh, OK. I see what you're talking about there, but how did dinosaurs legs look?

Dino: Well, have a look at this skeleton of a Stegosaurus. This fellow lived in North America millions of years ago, and its feet are directly underneath it. Dinosaurs' legs were kind of like posts or pillows that held up their heavy bodies. If their legs stuck out to the sides, they wouldn't be able to stand up! So, dinosaurs had their feet directly underneath them, while other reptiles like lizards, alligators and Komodo dragons have legs and feet that stick out to the sides. Not that there's anything wrong with that, I mean some of my best friends are lizards and alligators, they're just not dinosaurs.

Jessi: Cool! I've learned something already! Well, how else could you tell an animal that lived a long time ago was a dinosaur?

Dino: A lot of things the dinosaurs had in common weren't so much about how they looked but about how they lived. For example, dinosaurs only lived on land, they didn't live in water and they couldn't fly.

Jessi: Couldn't fly? Really?

Dino: Really! You've probably seen pictures of an animal like this before, right? They were amazing flying reptiles and they lived back in the time of the dinosaurs, but they weren't dinosaurs. They were pterosaurs, a whole different type of ancient reptile. Unlike the dinosaurs, they had hollow bones and big flaps of skin like wings which they used to fly. They also had really long narrow skulls with big brains inside, but dinosaurs didn't have any of those things. I mean, I've never seen a T-rex with wings, have you?

Jessi: No. No, I can't say that I have. But you also said that dinosaurs didn't live in the water?

Dino: Nope. They only lived on land. There were all kinds of huge reptiles that lived in the oceans back in dinosaur times, but none of them were dinosaurs. They were different in a lot of ways, like some were called plesiosaurs and didn't lay eggs like dinosaurs did, they just gave birth to live babies. Can you believe that!?

And another kind of swimming reptile were the mosasaurs. They were actually related more to snakes than to dinosaurs. Just like snakes, they could open their mouths so wide that they could actually eat things that were bigger than their own heads! Kind of wish I could do that, especially with apples. I love me some apples.

Jessi: So I can see from the fins and flippers on these swimming reptiles that they were adapted to life in the water. So if I see a fossil or picture of a reptile that lived a long time ago that has fins and flippers, I know it's not a dinosaur, right?

Dino: That's right, Jessi! Dinosaurs lived only on land, and stood with their feet right under them, instead of to the sides.

Jessi: Got it. Tanks for sharing what you've learned with us, Dino.

Dino: Oh, believe me Jessi, I could go on all day.

Jessi: Oh, I bet you could. Do you have any questions about dinosaurs, or nature or outer space or machines? Let us know by leaving a comment or emailing us at kids@thescishow.com and we'll see you next time.

Dino: Have a T-rexellent day!

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