WEBVTT 00:00:00.984 --> 00:00:04.769 Shall I ask for a show of hands or a clapping 00:00:06.144 --> 00:00:08.244 of people in different generations? 00:00:08.268 --> 00:00:11.976 I'm interested in how many are three to 12 years old. NOTE Paragraph 00:00:12.000 --> 00:00:17.250 (Laughter) NOTE Paragraph 00:00:17.274 --> 00:00:18.560 None, huh? NOTE Paragraph 00:00:18.584 --> 00:00:19.959 (Laughter) 00:00:19.983 --> 00:00:21.190 All right. 00:00:21.809 --> 00:00:23.567 I'm going to talk about dinosaurs. 00:00:23.591 --> 00:00:25.976 Do you remember dinosaurs when you were that age? NOTE Paragraph 00:00:26.000 --> 00:00:31.467 (Applause) NOTE Paragraph 00:00:33.595 --> 00:00:35.976 Dinosaurs are kind of funny, you know. NOTE Paragraph 00:00:36.000 --> 00:00:38.497 (Laughter) NOTE Paragraph 00:00:38.521 --> 00:00:41.430 We're going to kind of go in a different direction right now. 00:00:41.454 --> 00:00:42.976 I hope you all realize that. 00:00:43.554 --> 00:00:45.785 So I'll just give you my message up front: 00:00:46.355 --> 00:00:47.970 Try not to go extinct. NOTE Paragraph 00:00:47.994 --> 00:00:49.332 (Laughter) NOTE Paragraph 00:00:49.356 --> 00:00:50.542 That's it. NOTE Paragraph 00:00:50.566 --> 00:00:54.976 (Laughter) NOTE Paragraph 00:00:55.919 --> 00:00:57.117 People ask me a lot -- 00:00:58.014 --> 00:01:00.666 in fact, one of the most asked questions I get 00:01:00.690 --> 00:01:03.976 is, why do children like dinosaurs so much? 00:01:04.000 --> 00:01:05.976 What's the fascination? 00:01:06.481 --> 00:01:08.976 And I usually just say, 00:01:09.000 --> 00:01:10.976 "Well, dinosaurs were big, 00:01:11.831 --> 00:01:13.976 different and gone." 00:01:15.196 --> 00:01:16.494 They're all gone. 00:01:16.518 --> 00:01:17.976 Well that's not true, 00:01:18.588 --> 00:01:20.723 but we'll get to the goose in a minute. 00:01:20.747 --> 00:01:23.244 So that's sort of the theme: 00:01:23.268 --> 00:01:25.898 big, different and gone. 00:01:27.144 --> 00:01:28.809 The title of my talk: 00:01:28.833 --> 00:01:30.875 Shape-shifting Dinosaurs: 00:01:30.899 --> 00:01:32.976 The cause of a premature extinction. NOTE Paragraph 00:01:34.005 --> 00:01:36.794 Now I assume that we remember dinosaurs. 00:01:36.818 --> 00:01:39.721 And there's lots of different shapes. 00:01:39.745 --> 00:01:42.198 Lots of different kinds. 00:01:42.222 --> 00:01:43.976 A long time ago, 00:01:44.690 --> 00:01:49.838 back in the early 1900s, museums were out looking for dinosaurs. 00:01:49.862 --> 00:01:51.975 They went out and gathered them up. 00:01:52.601 --> 00:01:54.368 And this is an interesting story. 00:01:55.203 --> 00:01:59.234 Every museum wanted a little bigger or better one than anybody else had. 00:01:59.258 --> 00:02:06.046 So if the museum in Toronto went out and collected a Tyrannosaur, a big one, 00:02:06.070 --> 00:02:10.014 then the museum in Ottawa wanted a bigger one, and a better one. 00:02:10.792 --> 00:02:12.620 And that happened for all museums. 00:02:12.644 --> 00:02:16.705 So everyone was out looking for all these bigger and better dinosaurs. 00:02:17.901 --> 00:02:20.118 And this was in the early 1900s. NOTE Paragraph 00:02:21.146 --> 00:02:23.976 By about 1970, 00:02:24.861 --> 00:02:29.161 some scientists were sitting around and they thought, "What in the world -- 00:02:29.715 --> 00:02:32.114 Look at these dinosaurs, they're all big. 00:02:33.752 --> 00:02:35.594 Where are all the little ones?" NOTE Paragraph 00:02:35.746 --> 00:02:37.428 (Laughter) NOTE Paragraph 00:02:38.574 --> 00:02:42.090 And they thought about it and they even wrote papers about it: 00:02:42.114 --> 00:02:43.976 "Where are the little dinosaurs?" NOTE Paragraph 00:02:44.000 --> 00:02:50.455 (Laughter) NOTE Paragraph 00:02:52.899 --> 00:02:55.976 Well, go to a museum, you'll see, 00:02:56.540 --> 00:02:58.976 see how many baby dinosaurs there are. 00:02:59.662 --> 00:03:02.449 People assumed -- and this was actually a problem -- 00:03:02.473 --> 00:03:06.777 people assumed that if they had little dinosaurs, 00:03:06.801 --> 00:03:10.503 if they had juvenile dinosaurs, they'd be easy to identify. 00:03:10.527 --> 00:03:14.400 You'd have a big dinosaur and a littler dinosaur. NOTE Paragraph 00:03:14.424 --> 00:03:15.725 (Laughter) NOTE Paragraph 00:03:15.866 --> 00:03:17.976 But all they had were big dinosaurs. NOTE Paragraph 00:03:18.983 --> 00:03:20.976 And it comes down to a couple of things. 00:03:21.000 --> 00:03:25.143 First off, scientists have egos, 00:03:25.778 --> 00:03:28.976 and scientists like to name dinosaurs. 00:03:29.655 --> 00:03:30.976 They like to name anything. 00:03:31.000 --> 00:03:34.957 Everybody likes to have their own animal that they named. NOTE Paragraph 00:03:34.981 --> 00:03:37.958 (Laughter) NOTE Paragraph 00:03:37.982 --> 00:03:41.289 And so every time they found something that looked a little different, 00:03:41.313 --> 00:03:43.166 they named it something different. 00:03:43.668 --> 00:03:45.070 And what happened, of course, 00:03:45.094 --> 00:03:48.761 is we ended up with a whole bunch of different dinosaurs. NOTE Paragraph 00:03:50.642 --> 00:03:52.976 In 1975, 00:03:54.296 --> 00:03:56.504 a light went on in somebody's head. 00:03:56.829 --> 00:04:01.054 Dr. Peter Dodson at the University of Pennsylvania 00:04:01.078 --> 00:04:07.835 actually realized that dinosaurs grew kind of like birds do, 00:04:08.668 --> 00:04:12.222 which is different than the way reptiles grow. 00:04:12.246 --> 00:04:13.826 And in fact, 00:04:13.850 --> 00:04:17.366 he used the cassowary as an example. 00:04:17.390 --> 00:04:20.441 And it's kind of cool -- if you look at the cassowary, 00:04:20.465 --> 00:04:23.692 or any of the birds that have crests on their heads, 00:04:23.716 --> 00:04:30.351 they grow to about 80 percent adult size before the crest starts to grow. 00:04:31.434 --> 00:04:32.976 Now think about that. 00:04:33.000 --> 00:04:35.976 They're basically retaining their juvenile characteristics 00:04:36.000 --> 00:04:39.520 very late in what we call ontogeny. 00:04:39.544 --> 00:04:45.474 So allometric cranial ontogeny is relative skull growth. 00:04:46.000 --> 00:04:52.432 So you can see that if you actually found one that was 80 percent grown 00:04:53.461 --> 00:04:56.886 and you didn't know that it was going to grow up to a cassowary, 00:04:56.910 --> 00:04:59.428 you would think they were two different animals. NOTE Paragraph 00:05:00.170 --> 00:05:02.976 So this was a problem, 00:05:03.000 --> 00:05:08.556 and Peter Dodson pointed this out using some duck-billed dinosaurs 00:05:09.062 --> 00:05:10.563 then called Hypacrosaurus. 00:05:10.587 --> 00:05:15.453 And he showed that if you were to take a baby and an adult 00:05:15.477 --> 00:05:18.778 and make an average of what it should look like, 00:05:18.802 --> 00:05:21.538 if it grew in sort of a linear fashion, 00:05:22.053 --> 00:05:25.994 it would have a crest about half the size of the adult. 00:05:26.236 --> 00:05:32.057 But the actual subadult at 65 percent had no crest at all. 00:05:32.321 --> 00:05:33.976 So this was interesting. 00:05:34.000 --> 00:05:39.452 So this is where people went astray again. 00:05:40.111 --> 00:05:42.718 I mean, if they'd have just taken that, 00:05:42.742 --> 00:05:45.760 taken Peter Dodson's work, and gone on with that, 00:05:45.784 --> 00:05:48.975 then we would have a lot less dinosaurs than we have. 00:05:49.658 --> 00:05:53.432 But scientists have egos; they like to name things. 00:05:54.120 --> 00:05:59.143 And so they went on naming dinosaurs because they were different. NOTE Paragraph 00:06:00.145 --> 00:06:02.798 Now we have a way of actually testing 00:06:02.822 --> 00:06:07.741 to see whether a dinosaur, or any animal, is a young one or an older one. 00:06:08.141 --> 00:06:11.392 And that's by actually cutting into their bones. 00:06:11.889 --> 00:06:18.663 But cutting into the bones of a dinosaur is hard to do, as you can imagine, 00:06:18.687 --> 00:06:23.731 because in museums, bones are precious. 00:06:25.842 --> 00:06:28.700 You go into a museum, and they take really good care of them. 00:06:28.724 --> 00:06:31.792 They put them in foam, little containers. 00:06:32.340 --> 00:06:34.084 They're very well taken care of. 00:06:36.172 --> 00:06:40.086 They don't like it if you come in and want to saw them open and look inside. NOTE Paragraph 00:06:40.110 --> 00:06:41.111 (Laughter) NOTE Paragraph 00:06:41.135 --> 00:06:44.544 So they don't normally let you do that. NOTE Paragraph 00:06:44.568 --> 00:06:45.569 (Laughter) NOTE Paragraph 00:06:45.593 --> 00:06:49.039 But I have a museum and I collect dinosaurs 00:06:50.127 --> 00:06:51.991 and I can saw mine open. 00:06:52.015 --> 00:06:53.992 So that's what I do. NOTE Paragraph 00:06:54.016 --> 00:06:58.691 (Applause) NOTE Paragraph 00:07:00.705 --> 00:07:03.362 So if you cut open a little dinosaur, 00:07:03.386 --> 00:07:06.076 it's very spongy inside, like A. 00:07:06.100 --> 00:07:08.976 And if you cut into an older dinosaur, it's very massive. 00:07:09.000 --> 00:07:12.077 You can tell it's mature bone. 00:07:12.101 --> 00:07:14.137 So it's real easy to tell them apart. 00:07:14.604 --> 00:07:18.309 So what I want to do is show you these. 00:07:18.333 --> 00:07:22.234 In North America in the northern plains of the United States 00:07:22.258 --> 00:07:25.976 and the southern plains of Alberta and Saskatchewan, 00:07:26.000 --> 00:07:29.726 there's this unit of rock called the Hell Creek Formation 00:07:29.750 --> 00:07:33.201 that produces the last dinosaurs that lived on Earth. 00:07:33.225 --> 00:07:36.149 And there are 12 of them that everyone recognizes -- 00:07:36.173 --> 00:07:39.975 I mean the 12 primary dinosaurs that went extinct. 00:07:40.613 --> 00:07:43.322 And so we will evaluate them. 00:07:44.139 --> 00:07:46.095 And that's sort of what I've been doing. 00:07:46.119 --> 00:07:51.250 So my students, my staff, we've been cutting them open. 00:07:51.814 --> 00:07:55.657 Now as you can imagine, cutting open a leg bone is one thing, 00:07:55.681 --> 00:07:58.740 but when you go to a museum 00:07:58.764 --> 00:08:02.975 and say, "You don't mind if I cut open your dinosaur's skull, do you?" 00:08:03.454 --> 00:08:05.976 they say, "Go away." NOTE Paragraph 00:08:06.000 --> 00:08:10.976 (Laughter) NOTE Paragraph 00:08:13.548 --> 00:08:14.976 So here are 12 dinosaurs. 00:08:15.000 --> 00:08:18.223 And we want to look at these three first. NOTE Paragraph 00:08:18.745 --> 00:08:22.119 So these are dinosaurs that are called Pachycephalosaurus. 00:08:22.143 --> 00:08:25.773 And everybody knows that these three animals are related. 00:08:25.797 --> 00:08:32.098 And the assumption is that they're related like cousins or whatever. 00:08:32.122 --> 00:08:37.958 But no one ever considered that they might be more closely related. 00:08:37.982 --> 00:08:39.206 In other words, 00:08:39.230 --> 00:08:41.976 people looked at them and they saw the differences. 00:08:42.585 --> 00:08:45.976 And you all know that if you are going to determine 00:08:46.000 --> 00:08:48.906 whether you're related to your brother or your sister, 00:08:48.930 --> 00:08:51.976 you can't do it by looking at differences. 00:08:52.690 --> 00:08:56.191 You can only determine relatedness by looking for similarities. NOTE Paragraph 00:08:56.215 --> 00:08:58.214 So people were looking at these 00:08:58.238 --> 00:09:00.671 and they were talking about how different they are. 00:09:00.695 --> 00:09:04.119 Pachycephalosaurus has a big, thick dome on its head, 00:09:04.143 --> 00:09:06.840 and it's got some little bumps on the back of its head, 00:09:06.864 --> 00:09:09.976 and it's got a bunch of gnarly things on the end of its nose. 00:09:10.790 --> 00:09:16.546 And then Stygimoloch, another dinosaur from the same age, lived at the same time, 00:09:16.570 --> 00:09:18.736 has spikes sticking out the back of its head. 00:09:18.760 --> 00:09:20.732 It's got a little, tiny dome, 00:09:20.756 --> 00:09:23.581 and it's got a bunch of gnarly stuff on its nose. 00:09:24.289 --> 00:09:27.976 And then there's this thing called Dracorex hogwartsia. 00:09:29.227 --> 00:09:30.657 Guess where that came from? 00:09:30.681 --> 00:09:31.845 Dragon. 00:09:31.869 --> 00:09:35.621 So here's a dinosaur that has spikes sticking out of its head, 00:09:35.645 --> 00:09:38.975 no dome and gnarly stuff on its nose. NOTE Paragraph 00:09:39.484 --> 00:09:42.230 Nobody noticed the gnarly stuff sort of looked alike. 00:09:43.102 --> 00:09:44.701 But they did look at these three 00:09:44.725 --> 00:09:47.180 and they said, "These are three different dinosaurs, 00:09:47.204 --> 00:09:50.118 and Dracorex is probably the most primitive of them. 00:09:50.142 --> 00:09:54.052 And the other one is more primitive than the other." 00:09:54.156 --> 00:09:58.257 It's unclear to me how they actually sorted these three of them out. 00:09:58.281 --> 00:10:00.174 But if you line them up, 00:10:00.198 --> 00:10:03.253 if you just take those three skulls and just line them up, 00:10:03.277 --> 00:10:05.264 they line up like this. 00:10:05.288 --> 00:10:07.344 Dracorex is the littlest one, 00:10:07.368 --> 00:10:09.977 Stygimoloch is the middle-size one, 00:10:10.001 --> 00:10:11.976 Pachycephalosaurus is the largest one. 00:10:12.000 --> 00:10:15.976 And one would think, that should give me a clue. NOTE Paragraph 00:10:16.000 --> 00:10:18.329 (Laughter) NOTE Paragraph 00:10:18.353 --> 00:10:19.883 But it didn't give them a clue. NOTE Paragraph 00:10:19.907 --> 00:10:21.081 (Laughter) NOTE Paragraph 00:10:21.105 --> 00:10:24.180 Because, well we know why. 00:10:24.204 --> 00:10:27.343 Scientists like to name things. NOTE Paragraph 00:10:28.668 --> 00:10:31.404 So if we cut open Dracorex -- 00:10:31.428 --> 00:10:33.353 I cut open our Dracorex -- 00:10:33.377 --> 00:10:37.601 and look, it was spongy inside, really spongy inside. 00:10:37.625 --> 00:10:41.324 I mean, it is a juvenile and it's growing really fast. 00:10:41.904 --> 00:10:43.891 So it is going to get bigger. 00:10:43.915 --> 00:10:47.553 If you cut open Stygimoloch, it is doing the same thing. 00:10:47.577 --> 00:10:51.207 The dome, that little dome, is growing really fast. 00:10:51.231 --> 00:10:52.923 It's inflating very fast. 00:10:53.564 --> 00:10:56.940 What's interesting is the spike on the back of the Dracorex 00:10:56.964 --> 00:10:59.043 was growing very fast as well. 00:10:59.067 --> 00:11:02.316 The spikes on the back of the Stygimoloch are actually resorbing, 00:11:02.340 --> 00:11:06.474 which means they're getting smaller as that dome is getting bigger. 00:11:06.498 --> 00:11:08.976 And if we look at Pachycephalosaurus, 00:11:09.000 --> 00:11:12.251 Pachycephalosaurus has a solid dome 00:11:12.275 --> 00:11:17.243 and its little bumps on the back of its head were also resorbing. NOTE Paragraph 00:11:17.267 --> 00:11:20.976 So just with these three dinosaurs, 00:11:21.000 --> 00:11:23.696 as a scientist, we can easily hypothesize 00:11:23.720 --> 00:11:27.975 that it is just a growth series of the same animal. 00:11:29.199 --> 00:11:31.690 Which of course means 00:11:32.962 --> 00:11:37.681 that Stygimoloch and Dracorex are extinct. NOTE Paragraph 00:11:37.705 --> 00:11:42.669 (Laughter) NOTE Paragraph 00:11:42.693 --> 00:11:44.030 OK. NOTE Paragraph 00:11:44.054 --> 00:11:45.204 (Laughter) NOTE Paragraph 00:11:46.947 --> 00:11:52.379 Which of course means we have 10 primary dinosaurs to deal with. NOTE Paragraph 00:11:53.234 --> 00:11:58.171 So a colleague of mine at Berkeley -- he and I were looking at Triceratops. 00:11:58.195 --> 00:12:00.510 And before the year 2000 -- 00:12:00.534 --> 00:12:04.206 now remember, Triceratops was first found in the 1800s -- 00:12:04.230 --> 00:12:09.395 before 2000, no one had ever seen a juvenile Triceratops. 00:12:10.362 --> 00:12:13.906 There's a Triceratops in every museum in the world, 00:12:13.930 --> 00:12:16.976 but no one had ever collected a juvenile. 00:12:18.418 --> 00:12:19.820 And we know why, right? 00:12:19.844 --> 00:12:21.976 Because everybody wants to have a big one. 00:12:22.844 --> 00:12:24.878 So everyone had a big one. 00:12:24.902 --> 00:12:27.310 So we went out and collected a whole bunch of stuff 00:12:27.334 --> 00:12:29.341 and we found a whole bunch of little ones. 00:12:29.365 --> 00:12:31.976 They're everywhere, they're all over the place. 00:12:32.584 --> 00:12:34.849 So we have a whole bunch of them at our museum. NOTE Paragraph 00:12:34.873 --> 00:12:39.323 (Laughter) NOTE Paragraph 00:12:39.347 --> 00:12:42.011 And everybody says it's because I have a little museum. 00:12:42.035 --> 00:12:44.755 When you have a little museum, you have little dinosaurs. NOTE Paragraph 00:12:44.779 --> 00:12:47.781 (Laughter) NOTE Paragraph 00:12:47.889 --> 00:12:49.631 If you look at the Triceratops, 00:12:49.655 --> 00:12:51.887 you can see it's changing, it's shape-shifting. 00:12:52.324 --> 00:12:55.854 As the juveniles are growing up, their horns actually curve backwards. 00:12:56.236 --> 00:12:59.901 And then as they get older, the horns grow forward. 00:12:59.925 --> 00:13:01.304 And that's pretty cool. 00:13:01.328 --> 00:13:03.643 If you look along the edge of the frill, 00:13:03.667 --> 00:13:08.833 they have these little triangular bones that actually grow big as triangles 00:13:08.857 --> 00:13:11.561 and then they flatten against the frill 00:13:11.585 --> 00:13:15.159 pretty much like the spikes do on the Pachycephalosaurs. 00:13:15.818 --> 00:13:20.299 And then, because the juveniles are in my collection, 00:13:20.323 --> 00:13:21.803 I cut them open ... NOTE Paragraph 00:13:21.827 --> 00:13:22.978 (Laughter) NOTE Paragraph 00:13:23.002 --> 00:13:24.176 and look inside. 00:13:24.200 --> 00:13:27.345 And the little one is really spongy. 00:13:27.369 --> 00:13:29.743 And the middle-size one is really spongy. 00:13:29.767 --> 00:13:34.642 But what was interesting was the adult Triceratops was also spongy. 00:13:34.666 --> 00:13:37.684 And this is a skull that is two meters long. 00:13:38.113 --> 00:13:39.976 It's a big skull. NOTE Paragraph 00:13:40.828 --> 00:13:45.475 But there's another dinosaur that is found in this formation 00:13:45.619 --> 00:13:49.102 that looks like a Triceratops, except it's bigger, 00:13:49.126 --> 00:13:51.094 and it's called Torosaurus. 00:13:51.955 --> 00:13:55.975 And Torosaurus, when we cut into it, has mature bone. 00:13:56.437 --> 00:13:58.479 But it's got these big holes in its shield. 00:13:58.503 --> 00:13:59.656 And everybody says, 00:13:59.680 --> 00:14:03.340 "A Triceratops and a Torosaurus can't possibly be the same animal 00:14:03.364 --> 00:14:05.856 because one of them's bigger than the other one." NOTE Paragraph 00:14:05.880 --> 00:14:10.515 (Laughter) NOTE Paragraph 00:14:10.539 --> 00:14:13.012 "And it has holes in its frill." 00:14:13.036 --> 00:14:15.995 And I said, "Well do we have any juvenile Torosauruses?" 00:14:16.019 --> 00:14:20.606 And they said, "Well, no, but it has holes in its frill." NOTE Paragraph 00:14:21.463 --> 00:14:24.915 So one of my graduate students, John Scannella, 00:14:24.939 --> 00:14:26.658 looked through our whole collection 00:14:26.682 --> 00:14:32.798 and he actually discovered that the hole starting to form in Triceratops 00:14:32.822 --> 00:14:35.957 and, of course it's open, in Torosaurus -- 00:14:35.981 --> 00:14:41.119 so he found the transitional ones between Triceratops and Torosaurus, 00:14:41.143 --> 00:14:42.375 which was pretty cool. 00:14:42.399 --> 00:14:48.530 So now we know that Torosaurus is actually a grown-up Triceratops. 00:14:49.964 --> 00:14:51.744 Now when we name dinosaurs, 00:14:51.768 --> 00:14:55.304 when we name anything, the original name gets to stick 00:14:55.328 --> 00:14:59.173 and the second name is thrown out. 00:14:59.936 --> 00:15:02.128 So Torosaurus is extinct. 00:15:03.441 --> 00:15:07.259 Triceratops, if you've heard the news, a lot of the newscasters got it all wrong. 00:15:07.283 --> 00:15:10.833 They thought Torosaurus should be kept and Triceratops thrown out, 00:15:10.857 --> 00:15:12.641 but that's not going to happen. NOTE Paragraph 00:15:12.665 --> 00:15:18.155 (Laughter) NOTE Paragraph 00:15:18.179 --> 00:15:21.462 All right, so we can do this with a bunch of dinosaurs. 00:15:21.486 --> 00:15:23.532 I mean, here's Edmontosaurus 00:15:23.556 --> 00:15:24.976 and Anatotitan. 00:15:25.423 --> 00:15:27.975 Anatotitan: giant duck. 00:15:28.632 --> 00:15:30.783 It's a giant duck-bill dinosaur. 00:15:30.807 --> 00:15:32.535 Here's another one. 00:15:32.559 --> 00:15:35.032 So we look at the bone histology. 00:15:35.056 --> 00:15:39.939 The bone histology tells us that Edmontosaurus is a juvenile, 00:15:39.963 --> 00:15:41.591 or at least a subadult, 00:15:41.615 --> 00:15:47.368 and the other one is an adult, and we have an ontogeny. 00:15:48.273 --> 00:15:50.226 And we get rid of Anatotitan. NOTE Paragraph 00:15:51.400 --> 00:15:53.221 So we can just keep doing this. 00:15:53.245 --> 00:15:56.581 And the last one is T. Rex. 00:15:57.332 --> 00:16:01.976 So there's these two dinosaurs, T. Rex and Nanotyrannus. NOTE Paragraph 00:16:02.000 --> 00:16:04.890 (Laughter) NOTE Paragraph 00:16:04.914 --> 00:16:07.630 Again, it makes you wonder. NOTE Paragraph 00:16:07.654 --> 00:16:10.864 (Laughter) NOTE Paragraph 00:16:10.888 --> 00:16:13.223 But they had a good question. 00:16:13.247 --> 00:16:16.132 They were looking at them and they said, "One's got 17 teeth, 00:16:16.156 --> 00:16:18.020 and the biggest one's got 12 teeth. 00:16:18.044 --> 00:16:19.914 And that doesn't make any sense at all, 00:16:19.938 --> 00:16:23.606 because we don't know of any dinosaurs that gain teeth as they get older. 00:16:23.630 --> 00:16:25.878 So it must be true -- 00:16:25.902 --> 00:16:27.195 they must be different." 00:16:28.643 --> 00:16:29.976 So we cut into them. 00:16:31.373 --> 00:16:35.250 And sure enough, Nanotyrannus has juvenile bone 00:16:35.274 --> 00:16:38.866 and the bigger one has more mature bone. 00:16:39.439 --> 00:16:41.842 It looks like it could still get bigger. 00:16:41.866 --> 00:16:44.087 And at the Museum of the Rockies where we work, 00:16:44.111 --> 00:16:47.750 I have four T. rexes, so I can cut a whole bunch of them. 00:16:47.774 --> 00:16:49.976 But I didn't have to cut any of them really, 00:16:50.000 --> 00:16:52.976 because I just lined up their jaws 00:16:53.000 --> 00:16:56.310 and it turned out the biggest one had 12 teeth 00:16:56.334 --> 00:16:58.509 and the next smallest one had 13 00:16:58.533 --> 00:17:00.763 and the next smallest had 14. 00:17:00.787 --> 00:17:02.810 And of course, Nano has 17. 00:17:02.834 --> 00:17:05.721 And we just went out and looked at other people's collections 00:17:05.745 --> 00:17:09.480 and we found one that has sort of 15 teeth. 00:17:09.504 --> 00:17:12.282 So again, real easy to say 00:17:12.306 --> 00:17:16.975 that Tyrannosaurus ontogeny included Nanotyrannus, 00:17:17.686 --> 00:17:22.325 and therefore we can take out another dinosaur. NOTE Paragraph 00:17:22.349 --> 00:17:23.976 (Laughter) NOTE Paragraph 00:17:27.377 --> 00:17:30.670 So when it comes down to our end Cretaceous, 00:17:30.694 --> 00:17:32.241 we have seven left. 00:17:34.099 --> 00:17:35.384 And that's a good number. 00:17:35.756 --> 00:17:38.976 That's a good number to go extinct, I think. 00:17:39.604 --> 00:17:40.838 Now as you can imagine, 00:17:40.862 --> 00:17:43.623 this is not very popular with fourth-graders. NOTE Paragraph 00:17:43.743 --> 00:17:44.744 (Laughter) NOTE Paragraph 00:17:44.768 --> 00:17:49.744 Fourth-graders love their dinosaurs, they memorize them. 00:17:53.113 --> 00:17:54.843 And they're not happy with this. NOTE Paragraph 00:17:54.867 --> 00:17:57.483 (Laughter) NOTE Paragraph 00:17:57.507 --> 00:17:58.698 Thank you very much. NOTE Paragraph 00:17:58.722 --> 00:18:02.626 (Applause)