1 00:00:00,984 --> 00:00:04,769 Shall I ask for a show of hands or a clapping 2 00:00:06,144 --> 00:00:08,244 of people in different generations? 3 00:00:08,268 --> 00:00:11,976 I'm interested in how many are three to 12 years old. 4 00:00:12,000 --> 00:00:17,250 (Laughter) 5 00:00:17,274 --> 00:00:18,560 None, huh? 6 00:00:18,584 --> 00:00:19,959 (Laughter) 7 00:00:19,983 --> 00:00:21,190 All right. 8 00:00:21,809 --> 00:00:23,567 I'm going to talk about dinosaurs. 9 00:00:23,591 --> 00:00:25,976 Do you remember dinosaurs when you were that age? 10 00:00:26,000 --> 00:00:31,467 (Applause) 11 00:00:33,595 --> 00:00:35,976 Dinosaurs are kind of funny, you know. 12 00:00:36,000 --> 00:00:38,497 (Laughter) 13 00:00:38,521 --> 00:00:41,430 We're going to kind of go in a different direction right now. 14 00:00:41,454 --> 00:00:42,976 I hope you all realize that. 15 00:00:43,554 --> 00:00:45,785 So I'll just give you my message up front: 16 00:00:46,355 --> 00:00:47,970 Try not to go extinct. 17 00:00:47,994 --> 00:00:49,332 (Laughter) 18 00:00:49,356 --> 00:00:50,542 That's it. 19 00:00:50,566 --> 00:00:54,976 (Laughter) 20 00:00:55,919 --> 00:00:57,117 People ask me a lot -- 21 00:00:58,014 --> 00:01:00,666 in fact, one of the most asked questions I get 22 00:01:00,690 --> 00:01:03,976 is, why do children like dinosaurs so much? 23 00:01:04,000 --> 00:01:05,976 What's the fascination? 24 00:01:06,481 --> 00:01:08,976 And I usually just say, 25 00:01:09,000 --> 00:01:10,976 "Well, dinosaurs were big, 26 00:01:11,831 --> 00:01:13,976 different and gone." 27 00:01:15,196 --> 00:01:16,494 They're all gone. 28 00:01:16,518 --> 00:01:17,976 Well that's not true, 29 00:01:18,588 --> 00:01:20,723 but we'll get to the goose in a minute. 30 00:01:20,747 --> 00:01:23,244 So that's sort of the theme: 31 00:01:23,268 --> 00:01:25,898 big, different and gone. 32 00:01:27,144 --> 00:01:28,809 The title of my talk: 33 00:01:28,833 --> 00:01:30,875 Shape-shifting Dinosaurs: 34 00:01:30,899 --> 00:01:32,976 The cause of a premature extinction. 35 00:01:34,005 --> 00:01:36,794 Now I assume that we remember dinosaurs. 36 00:01:36,818 --> 00:01:39,721 And there's lots of different shapes. 37 00:01:39,745 --> 00:01:42,198 Lots of different kinds. 38 00:01:42,222 --> 00:01:43,976 A long time ago, 39 00:01:44,690 --> 00:01:49,838 back in the early 1900s, museums were out looking for dinosaurs. 40 00:01:49,862 --> 00:01:51,975 They went out and gathered them up. 41 00:01:52,601 --> 00:01:54,368 And this is an interesting story. 42 00:01:55,203 --> 00:01:59,234 Every museum wanted a little bigger or better one than anybody else had. 43 00:01:59,258 --> 00:02:06,046 So if the museum in Toronto went out and collected a Tyrannosaur, a big one, 44 00:02:06,070 --> 00:02:10,014 then the museum in Ottawa wanted a bigger one, and a better one. 45 00:02:10,792 --> 00:02:12,620 And that happened for all museums. 46 00:02:12,644 --> 00:02:16,705 So everyone was out looking for all these bigger and better dinosaurs. 47 00:02:17,901 --> 00:02:20,118 And this was in the early 1900s. 48 00:02:21,146 --> 00:02:23,976 By about 1970, 49 00:02:24,861 --> 00:02:29,161 some scientists were sitting around and they thought, "What in the world -- 50 00:02:29,715 --> 00:02:32,114 Look at these dinosaurs, they're all big. 51 00:02:33,752 --> 00:02:35,594 Where are all the little ones?" 52 00:02:35,746 --> 00:02:37,428 (Laughter) 53 00:02:38,574 --> 00:02:42,090 And they thought about it and they even wrote papers about it: 54 00:02:42,114 --> 00:02:43,976 "Where are the little dinosaurs?" 55 00:02:44,000 --> 00:02:50,455 (Laughter) 56 00:02:52,899 --> 00:02:55,976 Well, go to a museum, you'll see, 57 00:02:56,540 --> 00:02:58,976 see how many baby dinosaurs there are. 58 00:02:59,662 --> 00:03:02,449 People assumed -- and this was actually a problem -- 59 00:03:02,473 --> 00:03:06,777 people assumed that if they had little dinosaurs, 60 00:03:06,801 --> 00:03:10,503 if they had juvenile dinosaurs, they'd be easy to identify. 61 00:03:10,527 --> 00:03:14,400 You'd have a big dinosaur and a littler dinosaur. 62 00:03:14,424 --> 00:03:15,725 (Laughter) 63 00:03:15,866 --> 00:03:17,976 But all they had were big dinosaurs. 64 00:03:18,983 --> 00:03:20,976 And it comes down to a couple of things. 65 00:03:21,000 --> 00:03:25,143 First off, scientists have egos, 66 00:03:25,778 --> 00:03:28,976 and scientists like to name dinosaurs. 67 00:03:29,655 --> 00:03:30,976 They like to name anything. 68 00:03:31,000 --> 00:03:34,957 Everybody likes to have their own animal that they named. 69 00:03:34,981 --> 00:03:37,958 (Laughter) 70 00:03:37,982 --> 00:03:41,289 And so every time they found something that looked a little different, 71 00:03:41,313 --> 00:03:43,166 they named it something different. 72 00:03:43,668 --> 00:03:45,070 And what happened, of course, 73 00:03:45,094 --> 00:03:48,761 is we ended up with a whole bunch of different dinosaurs. 74 00:03:50,642 --> 00:03:52,976 In 1975, 75 00:03:54,296 --> 00:03:56,504 a light went on in somebody's head. 76 00:03:56,829 --> 00:04:01,054 Dr. Peter Dodson at the University of Pennsylvania 77 00:04:01,078 --> 00:04:07,835 actually realized that dinosaurs grew kind of like birds do, 78 00:04:08,668 --> 00:04:12,222 which is different than the way reptiles grow. 79 00:04:12,246 --> 00:04:13,826 And in fact, 80 00:04:13,850 --> 00:04:17,366 he used the cassowary as an example. 81 00:04:17,390 --> 00:04:20,441 And it's kind of cool -- if you look at the cassowary, 82 00:04:20,465 --> 00:04:23,692 or any of the birds that have crests on their heads, 83 00:04:23,716 --> 00:04:30,351 they grow to about 80 percent adult size before the crest starts to grow. 84 00:04:31,434 --> 00:04:32,976 Now think about that. 85 00:04:33,000 --> 00:04:35,976 They're basically retaining their juvenile characteristics 86 00:04:36,000 --> 00:04:39,520 very late in what we call ontogeny. 87 00:04:39,544 --> 00:04:45,474 So allometric cranial ontogeny is relative skull growth. 88 00:04:46,000 --> 00:04:52,432 So you can see that if you actually found one that was 80 percent grown 89 00:04:53,461 --> 00:04:56,886 and you didn't know that it was going to grow up to a cassowary, 90 00:04:56,910 --> 00:04:59,428 you would think they were two different animals. 91 00:05:00,170 --> 00:05:02,976 So this was a problem, 92 00:05:03,000 --> 00:05:08,556 and Peter Dodson pointed this out using some duck-billed dinosaurs 93 00:05:09,062 --> 00:05:10,563 then called Hypacrosaurus. 94 00:05:10,587 --> 00:05:15,453 And he showed that if you were to take a baby and an adult 95 00:05:15,477 --> 00:05:18,778 and make an average of what it should look like, 96 00:05:18,802 --> 00:05:21,538 if it grew in sort of a linear fashion, 97 00:05:22,053 --> 00:05:25,994 it would have a crest about half the size of the adult. 98 00:05:26,236 --> 00:05:32,057 But the actual subadult at 65 percent had no crest at all. 99 00:05:32,321 --> 00:05:33,976 So this was interesting. 100 00:05:34,000 --> 00:05:39,452 So this is where people went astray again. 101 00:05:40,111 --> 00:05:42,718 I mean, if they'd have just taken that, 102 00:05:42,742 --> 00:05:45,760 taken Peter Dodson's work, and gone on with that, 103 00:05:45,784 --> 00:05:48,975 then we would have a lot less dinosaurs than we have. 104 00:05:49,658 --> 00:05:53,432 But scientists have egos; they like to name things. 105 00:05:54,120 --> 00:05:59,143 And so they went on naming dinosaurs because they were different. 106 00:06:00,145 --> 00:06:02,798 Now we have a way of actually testing 107 00:06:02,822 --> 00:06:07,741 to see whether a dinosaur, or any animal, is a young one or an older one. 108 00:06:08,141 --> 00:06:11,392 And that's by actually cutting into their bones. 109 00:06:11,889 --> 00:06:18,663 But cutting into the bones of a dinosaur is hard to do, as you can imagine, 110 00:06:18,687 --> 00:06:23,731 because in museums, bones are precious. 111 00:06:25,842 --> 00:06:28,700 You go into a museum, and they take really good care of them. 112 00:06:28,724 --> 00:06:31,792 They put them in foam, little containers. 113 00:06:32,340 --> 00:06:34,084 They're very well taken care of. 114 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. 115 00:06:40,110 --> 00:06:41,111 (Laughter) 116 00:06:41,135 --> 00:06:44,544 So they don't normally let you do that. 117 00:06:44,568 --> 00:06:45,569 (Laughter) 118 00:06:45,593 --> 00:06:49,039 But I have a museum and I collect dinosaurs 119 00:06:50,127 --> 00:06:51,991 and I can saw mine open. 120 00:06:52,015 --> 00:06:53,992 So that's what I do. 121 00:06:54,016 --> 00:06:58,691 (Applause) 122 00:07:00,705 --> 00:07:03,362 So if you cut open a little dinosaur, 123 00:07:03,386 --> 00:07:06,076 it's very spongy inside, like A. 124 00:07:06,100 --> 00:07:08,976 And if you cut into an older dinosaur, it's very massive. 125 00:07:09,000 --> 00:07:12,077 You can tell it's mature bone. 126 00:07:12,101 --> 00:07:14,137 So it's real easy to tell them apart. 127 00:07:14,604 --> 00:07:18,309 So what I want to do is show you these. 128 00:07:18,333 --> 00:07:22,234 In North America in the northern plains of the United States 129 00:07:22,258 --> 00:07:25,976 and the southern plains of Alberta and Saskatchewan, 130 00:07:26,000 --> 00:07:29,726 there's this unit of rock called the Hell Creek Formation 131 00:07:29,750 --> 00:07:33,201 that produces the last dinosaurs that lived on Earth. 132 00:07:33,225 --> 00:07:36,149 And there are 12 of them that everyone recognizes -- 133 00:07:36,173 --> 00:07:39,975 I mean the 12 primary dinosaurs that went extinct. 134 00:07:40,613 --> 00:07:43,322 And so we will evaluate them. 135 00:07:44,139 --> 00:07:46,095 And that's sort of what I've been doing. 136 00:07:46,119 --> 00:07:51,250 So my students, my staff, we've been cutting them open. 137 00:07:51,814 --> 00:07:55,657 Now as you can imagine, cutting open a leg bone is one thing, 138 00:07:55,681 --> 00:07:58,740 but when you go to a museum 139 00:07:58,764 --> 00:08:02,975 and say, "You don't mind if I cut open your dinosaur's skull, do you?" 140 00:08:03,454 --> 00:08:05,976 they say, "Go away." 141 00:08:06,000 --> 00:08:10,976 (Laughter) 142 00:08:13,548 --> 00:08:14,976 So here are 12 dinosaurs. 143 00:08:15,000 --> 00:08:18,223 And we want to look at these three first. 144 00:08:18,745 --> 00:08:22,119 So these are dinosaurs that are called Pachycephalosaurus. 145 00:08:22,143 --> 00:08:25,773 And everybody knows that these three animals are related. 146 00:08:25,797 --> 00:08:32,098 And the assumption is that they're related like cousins or whatever. 147 00:08:32,122 --> 00:08:37,958 But no one ever considered that they might be more closely related. 148 00:08:37,982 --> 00:08:39,206 In other words, 149 00:08:39,230 --> 00:08:41,976 people looked at them and they saw the differences. 150 00:08:42,585 --> 00:08:45,976 And you all know that if you are going to determine 151 00:08:46,000 --> 00:08:48,906 whether you're related to your brother or your sister, 152 00:08:48,930 --> 00:08:51,976 you can't do it by looking at differences. 153 00:08:52,690 --> 00:08:56,191 You can only determine relatedness by looking for similarities. 154 00:08:56,215 --> 00:08:58,214 So people were looking at these 155 00:08:58,238 --> 00:09:00,671 and they were talking about how different they are. 156 00:09:00,695 --> 00:09:04,119 Pachycephalosaurus has a big, thick dome on its head, 157 00:09:04,143 --> 00:09:06,840 and it's got some little bumps on the back of its head, 158 00:09:06,864 --> 00:09:09,976 and it's got a bunch of gnarly things on the end of its nose. 159 00:09:10,790 --> 00:09:16,546 And then Stygimoloch, another dinosaur from the same age, lived at the same time, 160 00:09:16,570 --> 00:09:18,736 has spikes sticking out the back of its head. 161 00:09:18,760 --> 00:09:20,732 It's got a little, tiny dome, 162 00:09:20,756 --> 00:09:23,581 and it's got a bunch of gnarly stuff on its nose. 163 00:09:24,289 --> 00:09:27,976 And then there's this thing called Dracorex hogwartsia. 164 00:09:29,227 --> 00:09:30,657 Guess where that came from? 165 00:09:30,681 --> 00:09:31,845 Dragon. 166 00:09:31,869 --> 00:09:35,621 So here's a dinosaur that has spikes sticking out of its head, 167 00:09:35,645 --> 00:09:38,975 no dome and gnarly stuff on its nose. 168 00:09:39,484 --> 00:09:42,230 Nobody noticed the gnarly stuff sort of looked alike. 169 00:09:43,102 --> 00:09:44,701 But they did look at these three 170 00:09:44,725 --> 00:09:47,180 and they said, "These are three different dinosaurs, 171 00:09:47,204 --> 00:09:50,118 and Dracorex is probably the most primitive of them. 172 00:09:50,142 --> 00:09:54,052 And the other one is more primitive than the other." 173 00:09:54,156 --> 00:09:58,257 It's unclear to me how they actually sorted these three of them out. 174 00:09:58,281 --> 00:10:00,174 But if you line them up, 175 00:10:00,198 --> 00:10:03,253 if you just take those three skulls and just line them up, 176 00:10:03,277 --> 00:10:05,264 they line up like this. 177 00:10:05,288 --> 00:10:07,344 Dracorex is the littlest one, 178 00:10:07,368 --> 00:10:09,977 Stygimoloch is the middle-size one, 179 00:10:10,001 --> 00:10:11,976 Pachycephalosaurus is the largest one. 180 00:10:12,000 --> 00:10:15,976 And one would think, that should give me a clue. 181 00:10:16,000 --> 00:10:18,329 (Laughter) 182 00:10:18,353 --> 00:10:19,883 But it didn't give them a clue. 183 00:10:19,907 --> 00:10:21,081 (Laughter) 184 00:10:21,105 --> 00:10:24,180 Because, well we know why. 185 00:10:24,204 --> 00:10:27,343 Scientists like to name things. 186 00:10:28,668 --> 00:10:31,404 So if we cut open Dracorex -- 187 00:10:31,428 --> 00:10:33,353 I cut open our Dracorex -- 188 00:10:33,377 --> 00:10:37,601 and look, it was spongy inside, really spongy inside. 189 00:10:37,625 --> 00:10:41,324 I mean, it is a juvenile and it's growing really fast. 190 00:10:41,904 --> 00:10:43,891 So it is going to get bigger. 191 00:10:43,915 --> 00:10:47,553 If you cut open Stygimoloch, it is doing the same thing. 192 00:10:47,577 --> 00:10:51,207 The dome, that little dome, is growing really fast. 193 00:10:51,231 --> 00:10:52,923 It's inflating very fast. 194 00:10:53,564 --> 00:10:56,940 What's interesting is the spike on the back of the Dracorex 195 00:10:56,964 --> 00:10:59,043 was growing very fast as well. 196 00:10:59,067 --> 00:11:02,316 The spikes on the back of the Stygimoloch are actually resorbing, 197 00:11:02,340 --> 00:11:06,474 which means they're getting smaller as that dome is getting bigger. 198 00:11:06,498 --> 00:11:08,976 And if we look at Pachycephalosaurus, 199 00:11:09,000 --> 00:11:12,251 Pachycephalosaurus has a solid dome 200 00:11:12,275 --> 00:11:17,243 and its little bumps on the back of its head were also resorbing. 201 00:11:17,267 --> 00:11:20,976 So just with these three dinosaurs, 202 00:11:21,000 --> 00:11:23,696 as a scientist, we can easily hypothesize 203 00:11:23,720 --> 00:11:27,975 that it is just a growth series of the same animal. 204 00:11:29,199 --> 00:11:31,690 Which of course means 205 00:11:32,962 --> 00:11:37,681 that Stygimoloch and Dracorex are extinct. 206 00:11:37,705 --> 00:11:42,669 (Laughter) 207 00:11:42,693 --> 00:11:44,030 OK. 208 00:11:44,054 --> 00:11:45,204 (Laughter) 209 00:11:46,947 --> 00:11:52,379 Which of course means we have 10 primary dinosaurs to deal with. 210 00:11:53,234 --> 00:11:58,171 So a colleague of mine at Berkeley -- he and I were looking at Triceratops. 211 00:11:58,195 --> 00:12:00,510 And before the year 2000 -- 212 00:12:00,534 --> 00:12:04,206 now remember, Triceratops was first found in the 1800s -- 213 00:12:04,230 --> 00:12:09,395 before 2000, no one had ever seen a juvenile Triceratops. 214 00:12:10,362 --> 00:12:13,906 There's a Triceratops in every museum in the world, 215 00:12:13,930 --> 00:12:16,976 but no one had ever collected a juvenile. 216 00:12:18,418 --> 00:12:19,820 And we know why, right? 217 00:12:19,844 --> 00:12:21,976 Because everybody wants to have a big one. 218 00:12:22,844 --> 00:12:24,878 So everyone had a big one. 219 00:12:24,902 --> 00:12:27,310 So we went out and collected a whole bunch of stuff 220 00:12:27,334 --> 00:12:29,341 and we found a whole bunch of little ones. 221 00:12:29,365 --> 00:12:31,976 They're everywhere, they're all over the place. 222 00:12:32,584 --> 00:12:34,849 So we have a whole bunch of them at our museum. 223 00:12:34,873 --> 00:12:39,323 (Laughter) 224 00:12:39,347 --> 00:12:42,011 And everybody says it's because I have a little museum. 225 00:12:42,035 --> 00:12:44,755 When you have a little museum, you have little dinosaurs. 226 00:12:44,779 --> 00:12:47,781 (Laughter) 227 00:12:47,889 --> 00:12:49,631 If you look at the Triceratops, 228 00:12:49,655 --> 00:12:51,887 you can see it's changing, it's shape-shifting. 229 00:12:52,324 --> 00:12:55,854 As the juveniles are growing up, their horns actually curve backwards. 230 00:12:56,236 --> 00:12:59,901 And then as they get older, the horns grow forward. 231 00:12:59,925 --> 00:13:01,304 And that's pretty cool. 232 00:13:01,328 --> 00:13:03,643 If you look along the edge of the frill, 233 00:13:03,667 --> 00:13:08,833 they have these little triangular bones that actually grow big as triangles 234 00:13:08,857 --> 00:13:11,561 and then they flatten against the frill 235 00:13:11,585 --> 00:13:15,159 pretty much like the spikes do on the Pachycephalosaurs. 236 00:13:15,818 --> 00:13:20,299 And then, because the juveniles are in my collection, 237 00:13:20,323 --> 00:13:21,803 I cut them open ... 238 00:13:21,827 --> 00:13:22,978 (Laughter) 239 00:13:23,002 --> 00:13:24,176 and look inside. 240 00:13:24,200 --> 00:13:27,345 And the little one is really spongy. 241 00:13:27,369 --> 00:13:29,743 And the middle-size one is really spongy. 242 00:13:29,767 --> 00:13:34,642 But what was interesting was the adult Triceratops was also spongy. 243 00:13:34,666 --> 00:13:37,684 And this is a skull that is two meters long. 244 00:13:38,113 --> 00:13:39,976 It's a big skull. 245 00:13:40,828 --> 00:13:45,475 But there's another dinosaur that is found in this formation 246 00:13:45,619 --> 00:13:49,102 that looks like a Triceratops, except it's bigger, 247 00:13:49,126 --> 00:13:51,094 and it's called Torosaurus. 248 00:13:51,955 --> 00:13:55,975 And Torosaurus, when we cut into it, has mature bone. 249 00:13:56,437 --> 00:13:58,479 But it's got these big holes in its shield. 250 00:13:58,503 --> 00:13:59,656 And everybody says, 251 00:13:59,680 --> 00:14:03,340 "A Triceratops and a Torosaurus can't possibly be the same animal 252 00:14:03,364 --> 00:14:05,856 because one of them's bigger than the other one." 253 00:14:05,880 --> 00:14:10,515 (Laughter) 254 00:14:10,539 --> 00:14:13,012 "And it has holes in its frill." 255 00:14:13,036 --> 00:14:15,995 And I said, "Well do we have any juvenile Torosauruses?" 256 00:14:16,019 --> 00:14:20,606 And they said, "Well, no, but it has holes in its frill." 257 00:14:21,463 --> 00:14:24,915 So one of my graduate students, John Scannella, 258 00:14:24,939 --> 00:14:26,658 looked through our whole collection 259 00:14:26,682 --> 00:14:32,798 and he actually discovered that the hole starting to form in Triceratops 260 00:14:32,822 --> 00:14:35,957 and, of course it's open, in Torosaurus -- 261 00:14:35,981 --> 00:14:41,119 so he found the transitional ones between Triceratops and Torosaurus, 262 00:14:41,143 --> 00:14:42,375 which was pretty cool. 263 00:14:42,399 --> 00:14:48,530 So now we know that Torosaurus is actually a grown-up Triceratops. 264 00:14:49,964 --> 00:14:51,744 Now when we name dinosaurs, 265 00:14:51,768 --> 00:14:55,304 when we name anything, the original name gets to stick 266 00:14:55,328 --> 00:14:59,173 and the second name is thrown out. 267 00:14:59,936 --> 00:15:02,128 So Torosaurus is extinct. 268 00:15:03,441 --> 00:15:07,259 Triceratops, if you've heard the news, a lot of the newscasters got it all wrong. 269 00:15:07,283 --> 00:15:10,833 They thought Torosaurus should be kept and Triceratops thrown out, 270 00:15:10,857 --> 00:15:12,641 but that's not going to happen. 271 00:15:12,665 --> 00:15:18,155 (Laughter) 272 00:15:18,179 --> 00:15:21,462 All right, so we can do this with a bunch of dinosaurs. 273 00:15:21,486 --> 00:15:23,532 I mean, here's Edmontosaurus 274 00:15:23,556 --> 00:15:24,976 and Anatotitan. 275 00:15:25,423 --> 00:15:27,975 Anatotitan: giant duck. 276 00:15:28,632 --> 00:15:30,783 It's a giant duck-bill dinosaur. 277 00:15:30,807 --> 00:15:32,535 Here's another one. 278 00:15:32,559 --> 00:15:35,032 So we look at the bone histology. 279 00:15:35,056 --> 00:15:39,939 The bone histology tells us that Edmontosaurus is a juvenile, 280 00:15:39,963 --> 00:15:41,591 or at least a subadult, 281 00:15:41,615 --> 00:15:47,368 and the other one is an adult, and we have an ontogeny. 282 00:15:48,273 --> 00:15:50,226 And we get rid of Anatotitan. 283 00:15:51,400 --> 00:15:53,221 So we can just keep doing this. 284 00:15:53,245 --> 00:15:56,581 And the last one is T. Rex. 285 00:15:57,332 --> 00:16:01,976 So there's these two dinosaurs, T. Rex and Nanotyrannus. 286 00:16:02,000 --> 00:16:04,890 (Laughter) 287 00:16:04,914 --> 00:16:07,630 Again, it makes you wonder. 288 00:16:07,654 --> 00:16:10,864 (Laughter) 289 00:16:10,888 --> 00:16:13,223 But they had a good question. 290 00:16:13,247 --> 00:16:16,132 They were looking at them and they said, "One's got 17 teeth, 291 00:16:16,156 --> 00:16:18,020 and the biggest one's got 12 teeth. 292 00:16:18,044 --> 00:16:19,914 And that doesn't make any sense at all, 293 00:16:19,938 --> 00:16:23,606 because we don't know of any dinosaurs that gain teeth as they get older. 294 00:16:23,630 --> 00:16:25,878 So it must be true -- 295 00:16:25,902 --> 00:16:27,195 they must be different." 296 00:16:28,643 --> 00:16:29,976 So we cut into them. 297 00:16:31,373 --> 00:16:35,250 And sure enough, Nanotyrannus has juvenile bone 298 00:16:35,274 --> 00:16:38,866 and the bigger one has more mature bone. 299 00:16:39,439 --> 00:16:41,842 It looks like it could still get bigger. 300 00:16:41,866 --> 00:16:44,087 And at the Museum of the Rockies where we work, 301 00:16:44,111 --> 00:16:47,750 I have four T. rexes, so I can cut a whole bunch of them. 302 00:16:47,774 --> 00:16:49,976 But I didn't have to cut any of them really, 303 00:16:50,000 --> 00:16:52,976 because I just lined up their jaws 304 00:16:53,000 --> 00:16:56,310 and it turned out the biggest one had 12 teeth 305 00:16:56,334 --> 00:16:58,509 and the next smallest one had 13 306 00:16:58,533 --> 00:17:00,763 and the next smallest had 14. 307 00:17:00,787 --> 00:17:02,810 And of course, Nano has 17. 308 00:17:02,834 --> 00:17:05,721 And we just went out and looked at other people's collections 309 00:17:05,745 --> 00:17:09,480 and we found one that has sort of 15 teeth. 310 00:17:09,504 --> 00:17:12,282 So again, real easy to say 311 00:17:12,306 --> 00:17:16,975 that Tyrannosaurus ontogeny included Nanotyrannus, 312 00:17:17,686 --> 00:17:22,325 and therefore we can take out another dinosaur. 313 00:17:22,349 --> 00:17:23,976 (Laughter) 314 00:17:27,377 --> 00:17:30,670 So when it comes down to our end Cretaceous, 315 00:17:30,694 --> 00:17:32,241 we have seven left. 316 00:17:34,099 --> 00:17:35,384 And that's a good number. 317 00:17:35,756 --> 00:17:38,976 That's a good number to go extinct, I think. 318 00:17:39,604 --> 00:17:40,838 Now as you can imagine, 319 00:17:40,862 --> 00:17:43,623 this is not very popular with fourth-graders. 320 00:17:43,743 --> 00:17:44,744 (Laughter) 321 00:17:44,768 --> 00:17:49,744 Fourth-graders love their dinosaurs, they memorize them. 322 00:17:53,113 --> 00:17:54,843 And they're not happy with this. 323 00:17:54,867 --> 00:17:57,483 (Laughter) 324 00:17:57,507 --> 00:17:58,698 Thank you very much. 325 00:17:58,722 --> 00:18:02,626 (Applause)