Extreme Dinosaurs
First shown: BBC Two 9.00pm Thursday 23rd November 2000

NARRATOR (PAUL BRIGHTWELL): Patagonia, Argentina. This is dinosaur country, a land where the rocks are rich with fossils. For millions of years this peaceful land has kept a terrible secret and only now are palaeontologists uncovering the truth. New finds here in South America are revolutionising our picture of the prehistoric world. It now seems that in the time of the dinosaurs Patagonia may have been the scene of the bloodiest battle in the history of life, one that matched the biggest animal ever to have walked the Earth against a new dinosaur, the most fearsome killer that ever evolved. A huge plant-eating dinosaur takes on a massive carnivore in an ugly pitched battle for survival.

This idea of the two biggest creatures on the planet locked in mortal combat has proved irresistible for science-fiction writers and movie makers, but for the scientists who study dinosaurs this was pure fantasy. They knew that this clash of Titans could never have happened in real life. That's because in real life the giant, long-necked herbivores never lived alongside the mega-carnivores, huge dinosaurs like Tyrannosaurus rex, the king of the meat-eaters. The two giants of their kind never walked the Earth at the same time in the same place. Creatures like these could never have met - or so the scientists thought.

Plaza Huincul, a small Argentinean town in rural Patagonia, is famous for two things: oil and dinosaurs. Palaeontologists come to the plains surrounding Plaza Huincul searching for clues to the prehistoric world. This place was one home to the most extreme dinosaurs the world has ever seen. Dinosaur hunter, Rodolfo Coria knows he's a lucky man. He's chief palaeontologist here and many of the most extraordinary finds have been his.

DR RODOLFO CORIA (Plaza Huincul Museum): Argentina is a good place for finding fossils, specially because of Patagonia. Patagonia is almost 50% of the Argentina surface and the rocks, they are very well exposed, so it's very easy to find fossil evidence on it. If you're looking for dinosaurs Patagonia is the place.

NARRATOR: But even Rodolfo was unprepared for the series of record-breaking monsters he was to unearth in these rocks, dinosaurs which would change our picture of the prehistoric world. It all began nine years ago when he and his team began excavating the bones of what was obviously a very large dinosaur. After many days of back-breaking digging they had revealed just part of an enormous skeleton. They then hauled whole chunks of rock back to the workshop to free the bones inside, but the amazing thing was when they chipped away at this massive hunk they found only one bone inside and when they calculated the size of the creature from the bones they realised they had found the biggest dinosaur that ever lived, a completely new species, a giant plant-eater. They named this new creature Argentinasaurus.

RODOLFO CORIA: This is a human backbone, this is a backbone of a whale and this is an Argentinasaurus backbone. You can see just on its size that Argentinasaurus was a very big animal.

NARRATOR: The other bones were just as massive. With thighs the size of a car, Argentinasaurus was far and away the heaviest dinosaur ever found. When this animal walked the earth trembled. The world of palaeontology was thrilled.

DR THOMAS HOLTZ (University of Maryland): It's an immense plant-eater, it's perhaps 80-100 metric tonnes, or to think of it another way, it's the size of a herd of elephants. it may be that there are dinosaurs even bigger than Argentinasaurus out there yet to be found, but at present that's as big as we know any land-living creature has ever been in the history of life.

NARRATOR: This life-sized replica of Argentinasaurus is being built for the town square in Plaza Huincul. When it's finished it will stand as tall as a 5-storey building. But it wasn't just this dinosaur's size that was out of the ordinary. When scientists analysed the layers of rock in which the skeleton was found they discovered something. Argentinasaurus, along with many smaller South American long-necks, had been living at the wrong time. This fact was to prove crucial. Layers of fossil-bearing rock have shown that dinosaurs roamed the planet for 180 million years. Over the course of this time hundreds of different species of dinosaur evolved and died out. By the middle of their time on Earth, the famous Jurassic period, the land was dominated by massive plant-eating dinosaurs, the long-necks. These giant animals lumbered slowly across the landscape in large herds. With tiny brains, the size of a golf ball, they were neither quick-witted nor fleet-footed, but they didn't need to be. Sheer size was their defence. Only the youngest or the sickest were at risk from smaller predators. The reign of the long-necks lasted for 60 million years and then they died out - no one knows why. By the end of the final age of dinosaurs, the Cretaceous period, things were very different. A new and more vicious species of dinosaur arrived on the scene - the massive, carnivorous Tyrannosaurus. They were enormous creatures. Indeed they were the biggest carnivores known and for the next 25 million years these huge meat-eaters preyed upon everything around them. These giant predators never met the long-necked herbivores. But there was a part of the world where the story of evolution took a different path - South America. Millions of years ago when dinosaurs first appeared, all the land was connected in one huge super-continent known as Pangaea, but over the ages Pangaea broke up into two giant land masses, one in the north and one in the south.

DR FERNANDO NOVAS (Argentina Museum of Natural Sciences): Probably around 100 million years ago South America became separated and then the fauna - the dinosaurs, the mammals, the rest of the fauna and flora start to evolve in the separate way, in different ways, different forms.

NARRATOR: After the continent split different dinosaurs evolved on each continent. While throughout the northern continents the giant long-necks died out, down south something extraordinary was happening. Here the huge long-necks not only survived, they just kept growing bigger and bigger.

RODOLFO CORIA: About 90 million years ago there was no such animal this big in other, in any other part of the world but in South America, these four-legged plant-eaters like Argentinasaurus, a typical South American kind of dinosaur. In this Cretaceous period they were highly successful in the southern hemisphere.

NARRATOR: But it wasn't just the long-necked plant-eaters that were different on the isolated continent of South America. Sealed off from the rest of the world, the vicious tyrannosaurs never reached here. In fact, in the time of the long-neck Argentinasaurus scientists could find no trace of any large meat-eaters stalking the continent, but all that was about to change. A few years after the discovery of Argentinasaurus Rodolfo and his team started exploring a new fossil location near Plaza Huincul. Little did they realise what a fiercesome creature they would uncover. Buried for 95 million years a new monster began to emerge from its rocky grave. When they put the bones together they found they had uncovered their second record-breaking dinosaur. This was a truly astonishing find. They'd found another giant, but this wasn't a long-necked plant-eater, it was the skeleton of the biggest meat-eating dinosaur that ever lived. It was a completely new species of animal, unrelated to the tyrannosaurs and it was huge, the first giant carnivore ever discovered in South America. They called it Giganotosaurus.

THOMAS HOLTZ: Giganotosaurus is perhaps 10-15% more massive and longer than Tyrannosaurus rex which for a long time was the record holder.

FERNANDO NOVAS: Giganotosaurus was an incredible animal, around 13 metres in length. The head was huge, around one metres and 80 centimetres.

NARRATOR: Giganotosaurus had a skull the length of a man, but this giant predator had one more thing to reveal. When the team dated the bones they found that Giganotosaurus lived in the Cretaceous, the time of the giant long-neck, Argentinasaurus, and the two dinosaurs were found only 80 kilometres apart. For the first time anywhere in the world scientists had discovered mega-carnivores and huge plant-eaters living during the same time period and in the same place.

RODOLFO CORIA: This is a peculiar ecological relationship that we, that we found in, in Patagonia. Big preys and big predators.

THOMAS HOLTZ: If we look at South America in the age of Giganotosaurus the main potential prey for this immense meat-eater is an even more immense plant-eater, the giant Argentinasaurus.

NARRATOR: Could it be true that in Patagonia something unique happened? That the largest plant-eater ever to walk the Earth came face to face with the largest known meat-eater in an extraordinary clash of the Titans? Could this really ever have happened? As palaeontologists considered the idea of such an epic battle, they immediately saw a problem. The giant meat-eater, Giganotosaurus, may have been large, but he was still no match for Argentinasaurus. There was no way even this big meat-eater would have been able to kill such a huge animal. No way that is unless Giganotosaurus did what many others predators do when faced with a much bigger prey. For these hyenas hunting together is the only way they can bring down this wildebeest. Could this have been what the clash of Titans was really like, not with two solitary dinosaurs battling it out by themselves, but with a pack of marauding Giganotosaurus hunting one enormous Argentinasaurus? Unfortunately there was a fundamental problem with this idea. Palaeontologists have traditionally believed that large carnivorous dinosaurs lived and hunted alone. There was no evidence to support the idea of them as pack hunters and if they weren't pack hunters, they could never have attacked the massive long-neck Argentinasaurus. Angela Milner, like many palaeontologists, believes the mega-carnivores were solitary creatures.

DR ANGELA MILNER (The Natural History Museum): Traditional view of large meat-eating dinosaurs behaviour was that they were obviously large, perhaps very ferocious animals, perhaps rabid predators, but probably living singly. Large meat-eating dinosaurs, there's no real evidence at all that they worked together in big groups.

DR MATTHEW CARRANO (State University of New York): Pack hunting to me is something that's really hard to evolve and so unless there's a really good reason for it to be there I would, my default would be to say it's not there.

NARRATOR: For these sceptics there is some convincing evidence to support their view of solitary predators. These are footprints made by dinosaurs. They've been preserved in rock for over 150 million years. Mark Norell believes it's footprints like these that show which kinds of dinosaurs lived in groups.

DR MARK NORELL (American Museum of Natural History): The biggest of all dinosaurs, the giant plant-eating dinosaurs, have left trackways, fossilised footprints, which really, really show I think that they lived in groups or herds, or whatever you want to call them and these footprints are not arranged just randomly, they're arranged in groups which really show that large ones walked out in front of the pack, smaller ones in the middle of the pack and that these groups had a structure and that they're all going in the same direction.

MATTHEW CARRANO: And in some places you can follow them for long stretches, long distances, hundreds and thousands of metres and you can see that they all move, sometimes they all turn and it really seems to suggest that they're all moving together. It's not just a coincidence that they're all in the same direction.

MARK NORELL: So I think that this is really, really powerful evidence that's suggestive of this sort of behaviour in these animals. The evidence for giant carnivorous dinosaurs isn't as good.

MATTHEW CARRANO: We have meat-eating dinosaur footprints, but all of them seem to be solitary. Even when we have a trackway of several footprints in a row we never seem to have any trackways with it that show a group of animals moving together so whereas that is actually rather common for the plant-eating dinosaur footprints, it's essentially absent for the meat-eating dinosaur footprints.

NARRATOR: There's another key piece of evidence which supports the view that the plant-eating dinosaurs were group animals.

WALKIE-TALKIE VOICE: 242, this is 42. CO242 is entering the Natural Preserve.

NARRATOR: This desolate landscape contains a bone bed, a collection of dinosaur bones buried together. The fossilised remains of hundreds of plant-eating dinosaurs all of the same species who died together cover an area the size of a football pitch.

ANGELA MILNER: This bone bed was full of horned dinosaurs of different ages, little babies, large, full-grown ones and it's clear that they were probably crossing a swollen river and got drowned trying to cross.

NARRATOR: Sites like this where many plant-eating dinosaurs have been killed in an accident, lead palaeontologists to believe that these herbivores were living together in herds when they died together.

ANGELA MILNER: With plant-eating dinosaurs it's very frequent to find groups of animals preserved together in the rocks and because they're all associated together closely and there are mixed ages together, that's, that's good evidence they were living together as a herd.

NARRATOR: Bone beds containing herds of plant-eating dinosaurs are common, but there was no such convincing evidence that large meat-eating dinosaurs lived and died in groups.

THOMAS HOLTZ: In the case of the early fossil finds of meat-eating dinosaurs they sort of reinforce this idea of meat-eaters as solitary hunters. People had only found individual specimens of each of the species. They never found group assemblages, they never found a bunch of individuals together.

NARRATOR: All the evidence indicated that these vicious predators lived and died as solitary hunters and if they were solitary hunters, no single carnivore, however big, would have gone for a prey as huge as the giant herbivore, Argentinasaurus. It looked like the tantalising idea of a clash of the Titans down in Patagonia was doomed - or so most palaeontologists thought. But one man was going to change all that. Phil Currie is one of the world's most accomplished palaeontologists. He is one of the few scientists in the world who can identify any meat-eating dinosaur from a single tooth. It was Currie's passion for predatory dinosaurs that led him down south to work with Rodolfo Coria on the plains of Patagonia.

DR PHILIP CURRIE (Royal Tyrrell Museum of Palaeontology): When an opportunity came up in 1995 to go down to Argentina and see Rodolfo and all the fantastic fossil finds he'd made up to that point in time of course I jumped on it.

NARRATOR: Like his colleagues, Currie had always believed the mega-carnivores were solitary creatures and didn't hunt in packs, but over time as he began to think things through he made a connection.

PHILIP CURRIE: From looking at modern animals it became very clear that maybe it wasn't such an unusual thing that big, meat-eating dinosaurs were in fact packing animals. We'd already had good indications that the plant-eaters were herding animals and it'll only make sense that if the carnivores wanted to break the defences of a plant-eater's herd the only way they could do that is by having the strength of numbers and one of the responses that happens in a wide range of animals is that the meat-eaters become pack hunters.

NARRATOR: Currie now began to think the idea of large, meat-eating dinosaurs as pack hunters was a serious possibility, but to prove his hunch he needed hard evidence like that which had been found for the plant-eating dinosaurs. What he needed was to find a bone bed where a group of mega-carnivores, any meat-eating giants, no matter what species, lay buried together.

PHILIP CURRIE: If we can find a bone bed with a lot of carnivores in one place then we have an indication that those animals died together. If they died together it's a, it's a very high probability that they may have been living together.

THOMAS HOLTZ: The only way we can actually demonstrate if an animal's a group hunter or even come close to thinking about that, is by finding an assemblage where there are multiple individuals of different age sizes from small individuals all up the way through big adults buried together at the same time.

NARRATOR: So for Currie the search was on around the world for just such a site. And then he remembered something. Several years earlier he had read a very old magazine article by one of the most famous early dinosaur hunters.

PHILIP CURRIE: I'd read an article by Barnum Brown and the article was basically about his experiences in southern Alberta and in that article is basically a one-liner which suggests that he found somewhere where there was a lot of tyrannosaurs' remains in one single bone bed.

NARRATOR: Currie realised this long forgotten site might be the multiple carnivore bone bed he had been looking for, a place which showed that several tyrannosaurs had lived and died together, but buried in the pages of National Geographic for over 80 years the reference to the bone bed site had long been forgotten.

PHILIP CURRIE: I got really excited. I knew that this was a really special site and I felt that we had to re-find the site. It wasn't a matter any more that somewhere out there was a bone bed that we might be able to find, I had to find that site.

NARRATOR: Although finding this unique site had become crucial to Currie, there was a big problem. Barnum Brown had never written down where the site was. He died taking the secret of its location to the grave.

MARK NORELL: This is one of Barnum Brown's field books. There aren't too many of these which really exist, not because they've been lost, but just because Barnum Brown didn't take any notes and if you look at it really all it is, is just a list of specimens and field numbers. There's not much in here about his day-to-day activities, there's not anything about describing the geology of particular localities, except that the rocks were grey or something like that, or it took him three days to get a specimen out, so unlike a lot of palaeontologists of his time or even today he wasn't much of a note taker.

NARRATOR: But Currie really needed to find the site, so he scored Brown's archive looking for clues.

PHILIP CURRIE: We went and looked at everything in the archives we could get our hands on and we were lucky that amongst all that material were four photographs which were pretty good.

NARRATOR: The photographs had been taken by Brown around the dig site in 1910. Currie hoped that he could use the photos to pinpoint Brown's excavation, but all that was known was that the dig site lay somewhere in the badlands near the Red Deer River in western Canada. So in 1997 Currie and a team of palaeontologists set off by boat on an expedition down a 100 mile stretch of the Red Deer River following in the paddle strokes of Barnum Brown looking for the site, but the badlands of Canada stretch over hundreds of square miles with endless crags, hills and gullies that all look exactly the same. In all this vast land no one knew where this potential goldmine of fossils was located.

PHILIP CURRIE: The badlands are very, very complex. Unless you happen to have exactly the right angle and be there at exactly the same time of day as he took the photograph, chances are pretty good you can't relocate sites by using photographs.

NARRATOR: But as he studied the photographs more closely, Currie noticed something. In one of them Brown's assistant was working at the elusive site. Behind him was a distinctive ridge of hills. If Currie could find that ridge he could find the site.

PHILIP CURRIE: If you look at this particular photograph you can see a series of ridges with trees behind them and there's not that many places around here where you're going to get exactly that combination of ridges and trees, so if you can line yourself up properly with those ridges and trees then you know you're in the right area and then you have a very good chance of finding the quarry itself. Even so it was still like looking for a needle in a haystack. We spent a couple of days basically scouring the area looking for just the right combination of badlands as revealed in the photographs. Well the first day went by and we had no luck, but the next day it turned out to be the hottest day of the year and the expedition, which numbered about 16 people, basically ran out of water. By lunchtime everybody had gone back to camp except for me and I'm crazy enough I guess that I kept at it. I went through all the badlands here and as you can see these canyons are quite deep so going up and down them on the hottest day of the year is, is, is quite an effort. I was at a point over there and I suddenly realised that a ridge in this region looked like it might just have the right kind of viewpoint. Got to the top and as I mounted this ridge over here I could see that the trees and the ridge lined up exactly perfectly and I knew I had the site.

NARRATOR: Currie and his team pounced on this unique site and started digging and it was worth it. What they found were the remains of several giant tyrannosaurs all together in one place. One after another they kept unearthing the bones of these huge, carnivorous dinosaurs.

PHILIP CURRIE: I don't know if Brown actually ever did a head count but the, the minimum number of animals in this quarry is definitely twelve.

NARRATOR: Twelve large meat-eating dinosaurs buried in the same place. It was an unprecedented find. Phil Currie had found the site that he had dreamt of, but there was more. As they examined the bones they had collected, it was clear that the dinosaurs they had excavated were of every age, from babies up to fully mature adults. It looked like a pack.

PHILIP CURRIE: The range of material is such that we can see that the smallest individual found in the bone bed was about four metres long and the largest individual found in the bone bed is about eleven metres long, so it's a pretty big range in size for this animal.

NARRATOR: They had found a whole pack of tyrannosaurs. Here at last was proof to Currie that the giant meat-eaters were not solitary creatures, that their traditional image was wrong. Instead the mega-carnivores may really have lived and hunted in groups. If that was true, then down in South America packs of Giganotosaurus might indeed have attacked prey as enormous as the immense long-neck Argentinasaurus. Currie's site seemed to prove it all, but other palaeontologists were not yet convinced.

MATTHEW CARRANO: Bone beds are very tantalising forms of information because you have a tremendous number of bones in one single layer and it's very tempting to look at that as evidence for a whole herd of these animals living in one place at one time. There are times when the bone bed information I think supports that interpretation, but there are times when it does not.

NARRATOR: Before anyone would accept Currie's evidence he would have to verify some key details about the dig site.

ANGELA MILNER: A collection of bones in a bone bed doesn't automatically mean we're looking at a collection of animals that lived together. Sometimes bone beds accumulate from large areas of the land where floods have brought all kinds of animal remains together and mixed them up, so you might be looking at an accumulation from, of many different animals from miles and miles away.

NARRATOR: This was the first problem. Flood waters spreading across the plains could have washed together the remains of several unrelated tyrannosaurs. Buried in the same place millions of years ago today they might look like a pack, but Currie felt he had an answer to this. These tyrannosaurs were rare dinosaurs. They would have made up only about 5% of the animal life in this area. The chances that twelve unrelated tyrannosaurs died separately and were washed together to this spot were minute.

PHILIP CURRIE: To find twelve Tyrannosaurus by chance at this level in this bone bed, the chances of that happening are about 1 in 64 million. It really isn't very likely that it's going to happen by chance.

NARRATOR: But there could be an even more dramatic reason why the bones of Currie's tyrannosaurs were all in one place. They could all have been caught in a predator trap. This is a predator trap. In this strange, swamp-like place molten tar has bubbled up from deep within the earth for tens of thousands of years. The sticky tar is lethal to any animal that wanders into it. Within seconds the creature will become stuck and then its fate is sealed. Predator traps have been found all around the world. This one is in downtown Los Angeles. John Harris has been investigating these tar pits for the past 20 years.

DR JOHN HARRIS (Page Museum, Los Angeles): What would happen would be a horse or a ground sloth or a camel would wander along and get stuck and just demonstrating here once it's in it takes a great deal of strength to pull it out and of course if an animal gets stuck on the surface like this when it's trying to pull out one leg it's push, pushing in three others and so very soon it will get totally immobilised.

NARRATOR: The trapped animal would lure predators to the swamp who would in turn become stuck.

JOHN HARRIS: There will be sort of meat on the hook waiting for the sabre-tooth and the, the, the dire wolf to come in and feed from it and they would come in and they in turn would get stuck and down would come the vultures to feed on them and they would get stuck and in would come the flies to feed off the carcasses and they'd get stuck so in pretty short order you'd build up an example of the whole food chain.

NARRATOR: Over time hundreds of dinosaur carcasses would have sunk into these traps. Millions of years later the tar and mud has turned to rock, the bones fossilised and the site would look like any normal rocky bone bed. If Currie's dig site was actually a prehistoric predator trap it would destroy his theory that the tyrannosaurs lived and hunted in packs, but how could the palaeontologists tell? There is always one tell-tale feature of all predator traps: they trap and kill every animal that is unlucky enough to cross their path. They contain the bones of many different species of animal that lived for miles around them.

JOHN HARRIS: Over the course of the last century we've recovered more than 3½ million fossils representing more than 650 species of animals and plants and they include a great diversity of animals, particularly large ones - mammoths, mastodons, sabre-tooth cats, lions, dire wolves and so on.

NARRATOR: If Currie's team discovered many different species of animal at their site they would have to consider whether they were simply the leftovers of a deadly predator trap, but after three years of painstaking digging there's been one extraordinary finding about this site.

PHILIP CURRIE: So far all of the animals that are found in here as parts of skeletons are one species and that's this big meat-eater, a tyrannosaur known as Albertasaurus. There are no other carnivorous dinosaurs in this bone bed and given that, we're dealing with only one type of carnivore. We can rule out things like predator traps. It's almost certain that these dinosaurs died here together because they were living together.

NARRATOR: Phil Currie seemed to have proved his case - but he hadn't. Although he was convinced, his fellow palaeontologists still weren't sure.

THOMAS HOLTZ: If we rely just on one site with large predatory dinosaurs found as a group with multiple individuals of different ages size buried together that could be a fluke, could be a chance.

MATTHEW CARRANO: The evidence right now is a little bit equivocal. It's not a definite set of evidence, it's a little circumstantial.

NARRATOR: Despite all his efforts, Currie's case was not yet proven. He now needed a second site if he was to convince his colleagues that the first dig wasn't a fluke, that large meat-eating dinosaurs really were pack hunters. And then he got some unexpected news. Patagonia, the land which had harboured the bones of Argentinasaurus and Giganotosaurus had yielded one further treasure. Phil Currie's colleague, Rodolfo Coria, had made a new discovery.

RODOLFO CORIA: We came here by chance first time because a local farmer called us because of some fossils that he had found and we were very lucky because looking in the slope of this hill we found this bone.

NARRATOR: This is one of the toe bones of what was to prove to be an enormous dinosaur. Rodolfo has recognised that the bone was from a meat-eater and the following year he had persuaded Phil Currie to join him down in Patagonia to try and find the rest of the skeleton.

PHILIP CURRIE: When we got there we actually found the level where the bones were coming from. As we dug into that level we realised there was a good part of a skeleton there. It far surpassed our expectations.

NARRATOR: Phil and Rodolfo thought the bones belonged to the giant carnivore, Giganotosaurus, but as they examined their new discoveries they noticed that the bones had different shapes from those of Giganotosaurus.

RODOLFO CORIA: This differences in the shape of the bones are a clue for palaeontologists to identify a new species and the shape is telling us that we are dealing with a new species of meat-eater.

NARRATOR: And then they began to measure the bones of their new beast. They were bigger than any meat-eater bones ever found anywhere in the world, bigger than T. rex, bigger even than Giganotosaurus.

PHILIP CURRIE: Our estimates show that a full size Tyrannosaurus rex was somewhere between 12 and 13 metres in total length and that means that the new one was somewhere between 14 and 15 metres in total length. It looks like we've probably got the biggest meat-eater in the world.

NARRATOR: But there was more. When Rodolfo and his team began to study the bone specimens in detail they noticed something strange. As they analysed the bones Rodolfo realised that they had found four leg bones for a two-legged creature. There was more than one carnivore in this dinosaur graveyard.

RODOLFO CORIA: So far our record is indicating that at least six individuals have been preserved.

NARRATOR: And what's more, they were all different ages. With six specimens of the new meat-eating dinosaur found at the Argentinean site, Phil Currie had what he needed: the second pack of mega-carnivores.

PHILIP CURRIE: I just couldn't believe it because suddenly here we were in a situation where we had two large meat-eating dinosaurs in two parts of the world which were showing packing behaviour. It seems to me that we have very convincing evidence that large meat-eating dinosaurs formed these social groups where the young and the old worked together, hunted together and lived together.

NARRATOR: Finally Currie's discoveries are beginning to convince others.

THOMAS HOLTZ: On the basis of these new discoveries we're beginning to have to shape and change our ideas on how large predators behaved. If they're operating as a group, if they're operating as a pack, a group of Giganotosaurus, for example, may have been able to mob even a big specimen of Argentinasaurus, something no one suspected before.

NARRATOR: But for Phil Currie this idea was more than a suspicion. It made perfect sense to him that the giant South American meat-eaters preyed upon the huge long-necks. He was convinced by their teeth.

PHILIP CURRIE: The teeth of the new animal are better adapted for going after really big dinosaurs, like the long-necked plant-eaters that lived in that region, because if you look at the teeth the teeth are very blade-like, they have serrations running down the front and the back and the teeth themselves are very narrow and knife-like.

THOMAS HOLTZ: This is a slicing tooth, this is a tooth designed to cut through meat so this new form could bite and slice up big chunks of flesh.

NARRATOR: Long-necks like Argentinasaurus had massive bones, impossible to crunch through, so the giant South American carnivores didn't even try. Instead Currie believes they used their thin, steak knife teeth to strip flesh from around the enormous bones.

PHILIP CURRIE: They were probably moving in to take quick bites slicing off only the flesh and not biting very deep at all and then when they had an opportunity they'd come in again and take another bite until the prey was weak enough that they could kill it.

NARRATOR: So when a group of these predators attacked together in a pack even a huge Argentinasaurus was doomed. It looks like the clash of Titans could really have happened after all.

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