When biting down hard on solid bone, most carnivorous dinosaur teeth would've been in danger of snapping. But Tyrannosaur teeth were stout enough to punch right through. Bone shattering teeth could've dealt crippling wounds. However, they came with a cost. Such teeth could only function properly with the aid of enormous jaw muscles. Inadequately muscled jaws would have made tyrannosaurs top heavy. Because they stood on their hind legs and held their spinal column parallel to the ground, carnivorous dinosaurs were built like a seesaw. Growing big jaw muscles added weight to the front half of the seesaw. The evolutionary solution was to shrink the arms, which reduced the total weight in the front and allow tyrannosaurus to stay balanced, but still gain biting power. This pattern of adaptive give and take is observable throughout the fossil record. Early tyrannosauroids had long arms with three fingered hands, but relatively weak jaws and compressed teeth. Gradually, over millions of years, the arms shrank, the jaws strengthened, and the teeth swelled. The ultimate result was the two-fingered, short-armed, powerfully jawed, and thick-toothed species Tyrannosaurus rex. The most common type of tyrannosaur found in Alberta is, not surprisingly, Albertosaurus. Now, Albertosaurus are slightly smaller versions of Tyrannosaurus rex. Never the less these are animals that would have been quite voracious. And, these are animals that you wouldn't wanted to have met in a dark alley by any stretch of the imagination. Tyrannosaurs are classically thought of as lone hunters. The reason we think of them that way is because their remains are relatively rare. In Alberta, for every Tyrannosaur skeleton we find, we find 19 skeletons of plant eating dinosaurs. Ankylosaurs, duck-billed dinosaurs, ceratopsian dinosaurs and so on. So, because they're so rare it's not unusual to find only one animal in one quarry. But in 1910 we know that something else happened. When I was in New York in 1996 looking at specimens collected by Barnum Brown. Brown's specimens included parts of nine skeletons of Albertosaurus. That were collected all from the same site on the Red Deer River. Now, this really excited me because if you can find nine skeletons in one single place on the Red Deer River, what does that mean for their behaviour. What does that mean for the ecosystem overall, of those dinosaurs from then. So, I went into the collections of the American Museum, and looked at the archives. Brown's field notes weren't very helpful. He just did not keep good field notes. He talked about the bone bed. He talked roughly where it was along the Red Deer River. But that's all the information we had. I could tell from the collection that he had made, that he realized that this was an important site. And he probably had an intention to publish a paper on the fact that he had found this site with so many Albertosaurus in one single place. But he never got around to it because he had so many dinosaur discoveries to report on that this specimen and the site eventually just got forgotten. Now, there were photographs as well in the collection. And using those photographs in 1997 we repeated Brown's trip by floating down the Red Deer river and trying to re-find the Albertosaurus bone bed. And one of those photographs turned out to be the winning combination of scenery and the right region as far as what the field notes and the letters in the American Museum suggested. And we found once again Brown's site. As suspected, Brown had not collected everything. He had only worked there for three weeks. The rock was pretty hard, and he only had one assistant at that time. So, what he collected was in fact the remains of individuals that could be counted on the basis of one single part of the body. And basically what he was doing was collecting just the feet, and these are articulated feet, where the bones are all together still. And he was collecting mostly left feet, and that told him how many individuals were represented in the bone bed. We suspected from the way that collection was made that Brown had not collected skulls, he had not collected vertebral columns, he had not collected the rest of the skeletons. And that that material should still be in the field. And when we refound the site in 1997 it became very evident that Brown had done exactly that. He had been high grading so that he would know exactly how many individuals were there. The curious thing is that Brown thought that all the smallest specimens that he collected. Which were very slender and elongate belong to not Tyrannosaurs, but to Ornithomimids. And we realize now that those were not Ornithomimids. They were in fact young Tyrannosaurs, and that those young Tyrannosaurs were built very differently in their body shape than the adult tyrannosaurs. In 1998 we reopened Barnum Brown's 1910 quarry, and we worked it until 2010, one century after brown had found the site. And in that time we increased the numbers of individuals. From the nine that Brown had known about to more than twenty individuals of Albertosaurus. We found the remains of some plant eating dinosaurs mixed in. Those plant eaters seemed to have been there incidentally they were bones that were washed in later on. They had nothing to do with the genesis of the Albertosaurus bone bed itself. So, here in one site in Alberta, we had more than 20 individuals in the same place. And because these animals are so rare, it was very clear that the incidence, or the recovery of all those individuals in one site was not accidental. There had to be a reason to explain why these animals had all died in the same place at the same time. And the best evidence we had looking at modern ecosystems and many of the fossil sites that have been studies in Alberta, is that perhaps these animals were gregarious at times, that is they moved in groups or they lived in groups. And that it was one of these gregarious groups that had suffered a mass death for some reason. About 70 million years ago. Now, looking at the evidence in the field, I think the evidence strongly confirmed that yes, these animals had died together. The interesting thing was that they consisted of individuals that were smaller than me. To animals that were as big as one of the smaller Tyrannosaurus rex specimens that is, they are animals that we know would've been anywhere from two years to more than 20 years old. The fact that they were different ages showed us they weren't together because they were breeding. So, what other explanations can you possibly have? And to try and explain it, we look to the modern world, to see what range of gregarious behavior is possible in modern carnivores. And I was very lucky, in 2010, to be able to go to Komodo National Park in Indonesia to look at Komodo dragons. Now, Komodo dragons are normally thought of as individuals but at certain times they become gregarious groups, and that's when food is available and at that time what they're capable of doing is working together to consume that available food. In my case I was able to watch them take apart the carcass of a wild boar. There were nine adult Komodo dragons and they tore it apart so efficiently even though their teeth are very small- smaller than my small fingernail they tore it apart so efficiently that twenty minutes since they started that wild boar that was larger than most of those Komodo dragons has been eaten completely. And all that remained was the smell of the boar itself. Now, that's one kind of gregarious behavior, all those animals were the same species, they outnumbered the plant eater and they were all in the same place at the same time. If there had been some catastrophe that happened then of course that could've explained why there were so many Komodo dragons or carnivores together at that one time. Now to look at the other other range of gregarious behavior. I was also lucky in 2010 to go to Africa. And night after night follow a pride of lions as it made its way. Trying to hunt food and take it down. And this was very interesting because they did it in a very different way than Komodo dragons. They were hunting cooperatively. And as they moved across the veld at nighttime and they became aware of potential prey, each one realized it had a different role. And without communicating with each other at least vocally in any way, they managed to encircle the potential prey and then of course attack it from all sides. So, co-operative hunting in lions is very famous and it's certainly the most sophisticated kind of gregarious behavior we see in hunters. Now, with animals like Albertosaurus, we don't exactly know what they're doing. We're looking at other kinds of clues. These are from something that happened 70 million years ago, so the clues are not always what you would like them to be. But the fact that we have both juveniles and adults in this pack of Albertosaurus along the Red Deer River strongly suggests that they weren't doing what Komodo dragons do. In the case of the Komodo dragons there was nine large individuals. They young were in the area. And they were hoping to get in on this too but they were afraid of the adults because they'll get eaten by the adults! And consequently they stay away from the whole thing. But in that case with the Komodo dragons the young never got to eat at all. In this case with the Albertosaurus it was more like a pride of lions. Small animals moving with large animals and taking part in the hunt. And with Albertosaurus we realize that those very lightly built, young animals were probably like young lions. They were faster and more agile, and maybe they took part in the hunt. By in fact being the ones that would move into the herds of large plant-eating dinosaurs and try and chase something out. And if they could kill it, of course they would do that. But if they couldn't kill it, what they would try and do was push that prey towards the ferocious jaws of the adults. And they would do the work. So, this kind of cooperation is possible, and it's fun to speculate on. I don't know if we'll ever prove it, but still, dinosaurs are more sophisticated than we generally think they are. Ornithomimids are one of the more specialized groups of theropod dinosaurs, in fact In some ways they don't even look like theropod, or meat eating dinosaurs because they lack teeth in their jaws. These dinosaurs are very bird-like in appearance and that's what gives them their name. Ornithomimid means 'bird mimic'. They're also in some cases called 'ostrich mimic' dinosaurs or Struthiomimus. This particular one comes from Alberta and it's called Dromiceiomimus, which means 'Emu mimic'. Basically, they're all quite similar in body form. And these dinosaurs have relatively small bodies. Most of them are not too much larger than a grown man today. But they all have long, hind legs, relatively small skulls, long arms, which are very different from what we see in tyrannosaurss, and when we look at all these features collectively, we can see that they're very bird-like overall. The skull itself lacks teeth and we know from some specimens that have been found in both Alberta and Mongolia, that in fact, there was a keratinous beak on the outside, looking very much like a modern ostrich that way. The brain is relatively large, and although we tend to think of birds having small brains, they in fact do have large brains and so does this dinosaur. The eyes are also very, very large and that certainly reinforces the similarity to a modern ostrich. These animals have long necks and the rib cage supports the arms which are quite long, as I mentioned. But the hands end in three claws, and these claws can be quite variable in appearance. Suggesting that different species of ornithomimids were in fact eating different things. When we go to the hind legs, the hind legs are very elongate and this animal stands about the same height as an ostrich. But if you looked at the leg proportions we'd see both similarities and differences. So, for example, we would see that like an ostrich, an ostrich mimic dinosaur, has very long lower leg parts. So, the tibia and fibula are quite elongate and the foot is also elongate; the flat earth foot elevates the animal well off the ground. The femur's a little bit different and the femur's longer in an ostrich mimic dinosaur and more mobile then what we'd see in a modern ostrich. Now, that's because the limb mechanics are in fact quite different in these two types of animals. In the ostrich you don't have a long tail. you have a short bony tail, and there's no way that the muscles that power the legs of these ostrich mimic dinosaurs could exist in an animal like a modern ostrich. Ornithomimids are without a doubt some of the fastest dinosaurs that ever lived. And these dinosaurs had their competition though, because in recent years we've realized that a close relative of the ostrich mimic dinosaurs, when it's young, a tyrannosaur in fact, looks very much like an ostrich mimic dinosaur in terms of its body proportions. So, those long legs of an ostrich mimic dinosaur probably had their match in baby tyrannosaurs and, for a time, they were using this great speed that these animals had just to escape tyrannosaurs, I'm sure. Ornithomimids mimic large, flightless birds in a number of ways. But which of the following traits do ornithomimids and ostriches not share? Is it, A, a toothless beak. B, long legs. C, a long muscular tail. Or D a body covering of feathers. The correct answer is C. Unlike modern birds, ornithomimids still had long muscular tails.
