0:00:07 > 0:00:08Dinosaurs.
0:00:08 > 0:00:13Masters of the planet for 160 million years.
0:00:17 > 0:00:20The biggest, baddest animals ever to walk the Earth.
0:00:22 > 0:00:25They had claws a foot long.
0:00:25 > 0:00:28And enormous, bone-crushing jaws
0:00:28 > 0:00:31with teeth the size of carving knives.
0:00:34 > 0:00:39Weighing up to 80 tons, the ground would literally shake when they moved.
0:00:43 > 0:00:45But how do we know so much about them?
0:00:46 > 0:00:50For over 40 years, Horizon and the BBC have followed
0:00:50 > 0:00:54the world's palaeontologists on their quest to find out
0:00:54 > 0:00:56what these elusive creatures were really like.
0:00:58 > 0:01:01As a palaeontologist, I love digging up the possibility
0:01:01 > 0:01:03of monsters of my childhood,
0:01:03 > 0:01:07looking for strange beasts that once roamed where I live now.
0:01:10 > 0:01:13Over time, with only bones and tiny fragments of information
0:01:13 > 0:01:16to go on, scientists have managed to piece together
0:01:16 > 0:01:21the complex jigsaw puzzle that is the life of the dinosaurs.
0:01:21 > 0:01:24There have been astonishing new finds,
0:01:24 > 0:01:26controversial theories...
0:01:28 > 0:01:32And extraordinary revelations about these giant reptiles.
0:01:32 > 0:01:34Quick, agile, fast-moving.
0:01:34 > 0:01:3715,000lbs of gut-crunching terror.
0:01:40 > 0:01:45These tantalising clues and breakthrough new technology have enabled scientists
0:01:45 > 0:01:49to reach for the answers to the biggest questions of all.
0:01:49 > 0:01:53Do we really know what happened to the dinosaurs?
0:01:53 > 0:01:57And is there a chance that some might still be alive today?
0:02:29 > 0:02:33When Horizon first began reporting on dinosaurs over 40 years ago,
0:02:33 > 0:02:37palaeontology was a science based on a lot of speculation
0:02:37 > 0:02:39and not that much evidence.
0:02:41 > 0:02:45Scientists really had just bits and pieces to go on.
0:02:47 > 0:02:52So it's hardly surprising that the dinosaurs we came to know and love
0:02:52 > 0:02:55were really just a mixture of fact and fantasy.
0:03:02 > 0:03:05The largest flesh eater the world has ever seen.
0:03:07 > 0:03:08I'm not afraid!
0:03:08 > 0:03:11All children now learn at an early age,
0:03:11 > 0:03:13but are reluctant to believe that tyrannosaurus
0:03:13 > 0:03:18and all the other dinosaurs followed a well-trod trail to oblivion.
0:03:18 > 0:03:20I see a little hole up in his nose.
0:03:20 > 0:03:23They've heard other stories about dinosaurs too,
0:03:23 > 0:03:24many of which are myths,
0:03:24 > 0:03:27replacing the fairy stories of earlier generations.
0:03:27 > 0:03:30For our limited knowledge of these pre-historic monsters
0:03:30 > 0:03:35provides numerous questions, but very few answers.
0:03:35 > 0:03:37CHILDREN LAUGH
0:03:40 > 0:03:44Look at that. Nine feet tall. What a monster.
0:03:48 > 0:03:52For years, scientists had grappled with fundamental questions.
0:03:52 > 0:03:56They didn't know what dinosaurs ate, how they bred.
0:03:58 > 0:04:02Sometimes they weren't even sure how the skeletons fitted together.
0:04:04 > 0:04:06They also couldn't work out
0:04:06 > 0:04:09whether one of the major groups of dinosaurs,
0:04:09 > 0:04:13the sauropods, lived on land or in water.
0:04:15 > 0:04:18But one of the first major finds covered by Horizon
0:04:18 > 0:04:21revealed evidence of sauropod behaviour frozen in time.
0:04:23 > 0:04:24Footprints.
0:04:26 > 0:04:29In the bed of the Paluxy river in Texas are tracks made
0:04:29 > 0:04:32by dinosaurs 70 million years ago,
0:04:32 > 0:04:35when the hard limestone rock was mud.
0:04:35 > 0:04:39This is evidence that convinces the most doubting tourist.
0:04:41 > 0:04:45Some are tracks of the meat-eating dinosaurs,
0:04:45 > 0:04:48Others of the heavy, long-necked, long-tailed dinosaurs.
0:04:48 > 0:04:50It is these which pose a problem.
0:04:50 > 0:04:54Were the creatures who made these tracks swamp dwellers,
0:04:54 > 0:04:56or did they move around on land?
0:04:56 > 0:04:5930 years ago, the river was dammed and the tracks photographed
0:04:59 > 0:05:03and carefully plotted. The shallowness of the footprints
0:05:03 > 0:05:07and the absence of tail marks suggested a herd of the animals
0:05:07 > 0:05:10living in water sufficiently deep to keep their tails out of the mud.
0:05:10 > 0:05:13It's difficult to believe that such huge creatures
0:05:13 > 0:05:17weighing up to 80 tons could support themselves out of water.
0:05:19 > 0:05:22But here is evidence for just that, a tail mark.
0:05:22 > 0:05:25If these creatures could support themselves out of water
0:05:25 > 0:05:28on one occasion, couldn't they be ordinary land dwellers
0:05:28 > 0:05:30who occasionally ventured to the swamps?
0:05:33 > 0:05:36At the time, a single tail mark was not enough to convince
0:05:36 > 0:05:42the palaeontologists that sauropods were anything but aquatic.
0:05:42 > 0:05:45But as more skeletons were discovered,
0:05:45 > 0:05:48their similarities to animals living on land became clearer.
0:05:50 > 0:05:54So then we have long straight limbs and a long neck,
0:05:54 > 0:05:56adaptations not for a hippo-like existence,
0:05:56 > 0:06:00but for living on land, feeding high on trees.
0:06:01 > 0:06:04Scientists looked again at the fossil footprints...
0:06:05 > 0:06:08And turned to living animals to try and determine how fast
0:06:08 > 0:06:10the sauropods could move.
0:06:13 > 0:06:17Dinosaur bones are only one source of information.
0:06:17 > 0:06:20Present day animals are another.
0:06:23 > 0:06:27Neil Alexander is Professor of Zoology at Leeds University.
0:06:27 > 0:06:30His main research interest is analysing how animals move.
0:06:30 > 0:06:33Recently he's found a way of applying his work
0:06:33 > 0:06:36to answering a seemingly impossible question.
0:06:36 > 0:06:37How fast did dinosaurs walk?
0:06:37 > 0:06:41On the beach at Southport, some vital evidence was laid out.
0:06:41 > 0:06:45These are replicas of some of the biggest footprints ever found.
0:06:45 > 0:06:49They were found in Texas, and they're not new footprints.
0:06:49 > 0:06:53They're footprints made something like 100 million years ago,
0:06:53 > 0:06:55preserved as fossils.
0:06:55 > 0:07:00Now, these big fellows, these are the hind feet.
0:07:00 > 0:07:02It was a four legged animal,
0:07:02 > 0:07:04and these hind feet
0:07:04 > 0:07:08are about three feet long. Stride length here of eight feet
0:07:08 > 0:07:11from right hind foot down to right hind foot down again.
0:07:14 > 0:07:18The dinosaur footprints are only part of the information needed.
0:07:18 > 0:07:21Now something called a Froude number has to be worked out.
0:07:21 > 0:07:24It's a mathematical formula relating the size of an animal's legs
0:07:24 > 0:07:27to the way its stride increases as it moves faster.
0:07:29 > 0:07:32Now we're going along at about five miles an hour,
0:07:32 > 0:07:34and the horse is walking.
0:07:34 > 0:07:36Each foot is moving in its own time.
0:07:36 > 0:07:39There are no two feet going together.
0:07:40 > 0:07:45We're going to speed up a bit, and then you'll see the gait change.
0:07:45 > 0:07:50If we go up now to about ten miles an hour, there we are...
0:07:52 > 0:07:57The diagonally opposite feet are moving together.
0:08:00 > 0:08:05Now if we speed up again and go further, there we are...
0:08:07 > 0:08:10Going through a canter into a full gallop.
0:08:10 > 0:08:16In the gallop, we've got the two forefeet moving about together,
0:08:16 > 0:08:20the two hind feet moving, again, about together.
0:08:24 > 0:08:27And now we must be going at something like 20 miles an hour.
0:08:30 > 0:08:33Professor Alexander has studied dozens of animals,
0:08:33 > 0:08:37from tiny gerbils to huge elephants, and worked out their Froude numbers.
0:08:37 > 0:08:39From these, he's able to estimate
0:08:39 > 0:08:42what the Froude number for any animal of any size will be.
0:08:43 > 0:08:47And so we find out what the Froude number is for the dinosaur,
0:08:47 > 0:08:50and how fast the dinosaur was going.
0:08:52 > 0:08:54And it's awful slow.
0:08:56 > 0:08:57Two miles an hour.
0:08:58 > 0:09:02Now, two miles an hour, that's a slow walk for a man.
0:09:02 > 0:09:05For something with legs three times as long as a man,
0:09:05 > 0:09:08it's a very slow walk indeed.
0:09:11 > 0:09:15Professor Alexander's work had reinforced the widely held view
0:09:15 > 0:09:19that dinosaurs were slow, lumbering reptiles.
0:09:25 > 0:09:28But the discovery of a new kind of dinosaur
0:09:28 > 0:09:30would change our thinking.
0:09:33 > 0:09:36We have right over here one that I discovered myself,
0:09:36 > 0:09:39which I think is one of the most interesting dinosaurs
0:09:39 > 0:09:42that's ever been found. In fact, I also think
0:09:42 > 0:09:45it's one of the most important dinosaurs ever found.
0:09:45 > 0:09:48Let me show you some interesting things
0:09:48 > 0:09:51about this fellow. First of all, it's a carnivorous dinosaur.
0:09:51 > 0:09:53But not a big one like tyrannosaurus,
0:09:53 > 0:09:54it's just a little fella,
0:09:54 > 0:09:58probably about four or five feet high,
0:09:58 > 0:10:01maybe about eight or nine feet in length.
0:10:01 > 0:10:04Weighed maybe about 175 pounds, about your weight or mine.
0:10:04 > 0:10:09One of the curious things about him is the construction of his foot.
0:10:09 > 0:10:14And the peculiar thing about this is the very large, sickle-like claw
0:10:14 > 0:10:15on the one toe.
0:10:15 > 0:10:20And remember that in addition to this long bony claw,
0:10:20 > 0:10:23there was a horny sheath that fit over that
0:10:23 > 0:10:26so that the total claw was probably half again as long.
0:10:26 > 0:10:28Obviously not designed for walking,
0:10:28 > 0:10:31and quite certainly an offensive weapon.
0:10:31 > 0:10:32This strange structure
0:10:32 > 0:10:37which we had never seen before in any of the carnivorous dinosaurs
0:10:37 > 0:10:41is the reason I coined the name for this that I did. Terrible claw. Deinonychus.
0:10:41 > 0:10:42But he was a fella
0:10:42 > 0:10:46I wouldn't want to meet on a dark street at night, I'll tell ya.
0:10:48 > 0:10:53John Ostrum realised Deinonychus was a ground-breaking dinosaur,
0:10:53 > 0:10:56one that overturned long-held ideas about how they moved.
0:10:56 > 0:10:59So the picture that we get from Deinonychus
0:10:59 > 0:11:01seems to be completely different
0:11:01 > 0:11:04from the old picture that we had of dinosaurs as sort of sluggish,
0:11:04 > 0:11:07sun-basking animals like modern lizards
0:11:07 > 0:11:11and turtles. Deinonychus seems to be a very quick, agile,
0:11:11 > 0:11:13fast-moving, two-legged predator.
0:11:13 > 0:11:19Good balance control means a high neurological development.
0:11:19 > 0:11:22This discovery is what sort of pushed me over the brink
0:11:22 > 0:11:24into looking at dinosaurs in a whole new light.
0:11:29 > 0:11:32Other dinosaurs too were suddenly seen as fast-moving, agile creatures.
0:11:37 > 0:11:41And Ostrum's new ideas about them developed like this.
0:11:41 > 0:11:45In the animal world, there's a major division. In one group,
0:11:45 > 0:11:48there are mammals which are active, hot-blooded creatures.
0:11:48 > 0:11:51In the other are reptiles, which are generally less active
0:11:51 > 0:11:53and cold-blooded.
0:11:53 > 0:11:55Where do dinosaurs fit?
0:11:55 > 0:11:57Since like mammals, they were very active,
0:11:57 > 0:12:01Ostrum reasoned perhaps they were hot-blooded too.
0:12:06 > 0:12:08This idea was revolutionary.
0:12:08 > 0:12:10Was it really possible that dinosaurs,
0:12:10 > 0:12:14ancient reptiles, could be warm-blooded?
0:12:19 > 0:12:22It would be another 30 years before deep bone analysis
0:12:22 > 0:12:25revealed that he might be right.
0:12:34 > 0:12:36For years, palaeontologists have been looking
0:12:36 > 0:12:38at the outsides of dinosaurs.
0:12:38 > 0:12:41+On the outsides, we can understand how dinosaurs evolved
0:12:41 > 0:12:43and their anatomy changed over time,
0:12:43 > 0:12:46but deep inside the bones, we can trace dinosaur life.
0:12:48 > 0:12:52By analysing thin cross-sections of fossilised dinosaur bone,
0:12:52 > 0:12:55Kristi Curry Rogers is helping to rewrite
0:12:55 > 0:12:58what we know about dinosaurs from the inside out.
0:12:58 > 0:13:01I think let's go with this one.
0:13:01 > 0:13:02And the smaller one.
0:13:02 > 0:13:05- Those two look good.- OK.
0:13:08 > 0:13:10One of the things we see
0:13:10 > 0:13:16when we crack open dinosaur bones is a story of a very fast growth rate
0:13:16 > 0:13:20throughout life history. We see that dinosaurs
0:13:20 > 0:13:24were growing very, very quickly on a par with modern mammals and birds,
0:13:24 > 0:13:25not like reptiles at all.
0:13:27 > 0:13:30This is a great example from a young Apatosaurus,
0:13:30 > 0:13:32a young, large sauropod dinosaur.
0:13:32 > 0:13:35All of these white spaces we see are places where blood vessels
0:13:35 > 0:13:38used to flow through this bone when the animal was still alive.
0:13:38 > 0:13:40This is completely different than the bone
0:13:40 > 0:13:43we might see of a reptile, like a crocodile, or a turtle.
0:13:43 > 0:13:46Instead this is lot more similar to those bones of mammals and birds.
0:13:46 > 0:13:51What she's discovered from deep within the dinosaur bones
0:13:51 > 0:13:55has reinforced the idea that at least some of them were warm-blooded.
0:13:56 > 0:13:59Dinosaurs, just like other modern animals,
0:13:59 > 0:14:04probably were fairly well adapted for whatever thermoregulatory strategy.
0:14:04 > 0:14:07I think they were perfectly well adapted to deal
0:14:07 > 0:14:10with the problems of maintaining a body temperature.
0:14:17 > 0:14:21Advances in technology were allowing scientists to break new ground,
0:14:21 > 0:14:24proving that dinosaurs weren't just giant lizards
0:14:24 > 0:14:27but a truly unique kind of reptile.
0:14:27 > 0:14:30But like a detective looking for clues,
0:14:30 > 0:14:34finding a whole dinosaur skeleton was the palaeontologists' dream
0:14:34 > 0:14:38and, in 1990, an American fossil-hunter hit the jackpot.
0:14:46 > 0:14:49For Pete Larson, and his then girlfriend Susan,
0:14:49 > 0:14:54the day had started as an ordinary, everyday fossil hunt.
0:14:54 > 0:14:57We were out actually digging on a triceratops skull
0:14:57 > 0:15:00that my ten-year-old son Matthew had found.
0:15:00 > 0:15:03We were just having a grand old time, it was a very nice, small triceratops skull.
0:15:03 > 0:15:07And all of a sudden, Susan walks up with a couple of bone fragments.
0:15:07 > 0:15:10And I said, "Is there more?"
0:15:10 > 0:15:11And she said, "There's lots more."
0:15:14 > 0:15:17Nothing could have prepared them for what they'd found.
0:15:19 > 0:15:24I looked up the face of the cliff and saw an expanse about eight feet wide
0:15:24 > 0:15:28and perhaps two feet deep with bones jutting out everywhere.
0:15:28 > 0:15:31And as I crawled up to the top of this exposure,
0:15:31 > 0:15:34I saw three articulated vertebra.
0:15:39 > 0:15:44I knew they had to come from a T rex because of the size of the curve of those bones,
0:15:44 > 0:15:47they were obviously parts of vertebrae
0:15:47 > 0:15:48from a meat-eating dinosaur.
0:15:50 > 0:15:53And when I saw those three articulated vertebrae,
0:15:53 > 0:15:57I knew this was going to be the most important specimen we'd ever dug up.
0:15:57 > 0:15:58I just knew it.
0:16:01 > 0:16:05Pete Larson marvelled at the size of the partially-exposed killer dinosaur.
0:16:08 > 0:16:11And nicknamed it "Sue" after his girlfriend.
0:16:13 > 0:16:16It was like clawing our way to the top of Mount Everest,
0:16:16 > 0:16:19and as we were uncovering it, we could see the top,
0:16:19 > 0:16:23and as we got her out of the ground, we were there.
0:16:23 > 0:16:25We had climbed the Mount Everest of palaeontology.
0:16:34 > 0:16:39We got the biggest, baddest of all the T rexs that ever was.
0:16:40 > 0:16:42And it got even better.
0:16:45 > 0:16:48Sue was extremely well preserved and nearly complete,
0:16:48 > 0:16:52exactly what Pete Larson had dreamed of finding.
0:16:52 > 0:16:57At long last, here was a chance to study the world's ultimate killing machine
0:16:57 > 0:16:59in extraordinary detail
0:16:59 > 0:17:02and all from just this one specimen.
0:17:33 > 0:17:36Deep within Sue's well-preserved skull,
0:17:36 > 0:17:41scientists were about to discover something they'd never seen before.
0:17:46 > 0:17:51And cutting edge technology would allow them to see it in exquisite detail.
0:17:53 > 0:17:57Basically, when it comes down to it, I was told to describe the thing inside and out
0:17:57 > 0:17:58I took that literally.
0:17:58 > 0:18:00I knew they wouldn't let me break the skull apart
0:18:00 > 0:18:03so CT scanning is the answer.
0:18:08 > 0:18:12CT scanning is an advanced x-ray imaging technique.
0:18:14 > 0:18:16It allowed Chris Brochu to build up
0:18:16 > 0:18:19computer images of slices through the head
0:18:19 > 0:18:22which he moulded together to produce
0:18:22 > 0:18:25a three-dimensional likeness of a T rex skull.
0:18:31 > 0:18:36Then, painstakingly, millimetre by millimetre, he followed the contours
0:18:36 > 0:18:41on the inside of the skull to reveal the structure of a T rex brain.
0:18:52 > 0:18:55The first time I saw the individual slices themselves,
0:18:55 > 0:18:57they didn't seem all that exciting.
0:18:57 > 0:19:00It wasn't until I built the first animation,
0:19:00 > 0:19:03the first flip through a bunch of slices all going through the skull,
0:19:03 > 0:19:06that was when it really struck me
0:19:06 > 0:19:08that there were a lot of things here to see.
0:19:10 > 0:19:16The CT scans revealed something scientists had never before been able to see in such detail.
0:19:20 > 0:19:24Protruding from the delicate network of brain tissue,
0:19:24 > 0:19:25was the optic nerve.
0:19:28 > 0:19:32This nerve was responsible for relaying information
0:19:32 > 0:19:35from the eyes to the visual centres in the brain.
0:19:37 > 0:19:40And it was big enough to carry a LOT of information.
0:19:43 > 0:19:46The scans seemed to confirm T rex did indeed
0:19:46 > 0:19:49have a key attribute of a skilled predator.
0:19:49 > 0:19:54It would have been able to seek out its prey at a distance
0:19:54 > 0:19:57and destroy it with the accuracy of an assassin.
0:20:04 > 0:20:08T rex could see its prey, but that didn't automatically make it
0:20:08 > 0:20:09an efficient killer.
0:20:09 > 0:20:12To get to grips with its enormous jaws,
0:20:12 > 0:20:15scientists devised a risky experiment.
0:20:15 > 0:20:16Watcha, watcha.
0:20:19 > 0:20:21Gators and crocodiles make a great model
0:20:21 > 0:20:23for studying the feeding biomechanics
0:20:23 > 0:20:24of extinct theropod dinosaurs.
0:20:24 > 0:20:29They have very similar musculature, and the basic leverage of their jaws
0:20:29 > 0:20:33and things like that are just a good analogy for tyrannosaur feeding.
0:20:36 > 0:20:38OK, grab that pole!
0:20:38 > 0:20:39Let's go.
0:20:42 > 0:20:46Watch your feet, watch your feet. Remember she can run forward.
0:20:46 > 0:20:50One, two, three...go, go, go!
0:20:50 > 0:20:51Watch your feet, Ray.
0:20:51 > 0:20:55This is a female American crocodile, Stevie.
0:20:55 > 0:20:59A youngster at 31 years old, she's only half the size she could become.
0:20:59 > 0:21:04She may be small, but her strength is obvious.
0:21:04 > 0:21:08Stay in line with her. Back up, back up, back up!
0:21:10 > 0:21:13- Back up. Who's got tape? - I have tape.
0:21:13 > 0:21:14She's heavy.
0:21:14 > 0:21:19Because her jaws are thought to work in a similar way to T rex jaws,
0:21:19 > 0:21:22Erickson plans to measure her bite to see what it may reveal
0:21:22 > 0:21:24about the power behind a T rex bite.
0:21:26 > 0:21:28Yet, as she's small and he's not tested her before,
0:21:28 > 0:21:32he has no idea what kind of results he'll get.
0:21:32 > 0:21:34All the way with that...
0:21:34 > 0:21:36I'm all set.
0:21:36 > 0:21:39Erickson needs to get the crocodile to crunch onto
0:21:39 > 0:21:42a specially-designed pressure sensor,
0:21:42 > 0:21:45which will record the force of the bite.
0:21:45 > 0:21:46OK, everybody ready?
0:21:46 > 0:21:50The tricky bit is getting the timing right.
0:21:50 > 0:21:52The bite needs to be a spontaneous one.
0:21:58 > 0:22:00Here we go. Hang on.
0:22:06 > 0:22:10819lbs. Good bite.
0:22:10 > 0:22:13An 800-lb bite is comparable to what a lion could do or
0:22:13 > 0:22:17a spotted hyena, which is the bone crushing champion among mammals.
0:22:17 > 0:22:20A very small crocodilian is capable of doing bite forces
0:22:20 > 0:22:24equal to what some of these large carnivoran mammals do.
0:22:24 > 0:22:28If you matched up an equal-sized crocodile say to a large lion,
0:22:28 > 0:22:31the crocodile will bite three times more forcefully.
0:22:31 > 0:22:33Watch your legs.
0:22:34 > 0:22:37If jaws like these give crocodiles a bite force
0:22:37 > 0:22:40well above what their weight implies,
0:22:40 > 0:22:43then Erickson believes the same must have been true of T rex jaws.
0:22:43 > 0:22:48His work suggested the power of a T rex bite
0:22:48 > 0:22:52may have been on a scale beyond anything we have ever seen.
0:22:52 > 0:22:53It's not a natural thing
0:22:53 > 0:22:57to stick your hand inside the mouth of a crocodile, but...
0:22:57 > 0:22:59Probably shouldn't try this at home, kids.
0:22:59 > 0:23:01To get an idea of how much more powerful,
0:23:01 > 0:23:06Erickson worked on doing more than just scale up the bite.
0:23:06 > 0:23:08Snout width is 14.2.
0:23:08 > 0:23:12He measured every physical detail of his crocodiles to try to map
0:23:12 > 0:23:15the differences in skull shape and body weight
0:23:15 > 0:23:19compared to an animal the size and shape of a T rex.
0:23:19 > 0:23:2250.2 head length...
0:23:22 > 0:23:26Erickson's preliminary maximum estimate of a T rex bite
0:23:26 > 0:23:30could be as much as 40,000lbs of force.
0:23:32 > 0:23:36That's about 50 times more powerful than our crocodile.
0:23:37 > 0:23:40T rex would have had easily the most powerful bite
0:23:40 > 0:23:43of any animal that has ever lived.
0:23:58 > 0:24:01The combination of new finds and advanced technology
0:24:01 > 0:24:04has enabled palaeontologists to interpret fossils
0:24:04 > 0:24:07with greater certainty.
0:24:07 > 0:24:10We now know more than ever before
0:24:10 > 0:24:13about what dinosaurs looked like,
0:24:13 > 0:24:19how fast they grew, their skill as predators,
0:24:19 > 0:24:20and how they moved.
0:24:24 > 0:24:28All building a convincing picture
0:24:28 > 0:24:31of how the dinosaurs came to dominate the Earth
0:24:31 > 0:24:32for over 160 million years.
0:24:41 > 0:24:44160 million years is a pretty long time
0:24:44 > 0:24:47and makes dinosaurs some of the most successful animals
0:24:47 > 0:24:48ever to have walked the Earth.
0:24:48 > 0:24:53After all, modern humans have only been around for a couple of hundred thousand years.
0:24:53 > 0:24:56Evidence of dinosaur life fills the geological record
0:24:56 > 0:24:59but then suddenly, 65 million years ago,
0:24:59 > 0:25:01it all disappeared.
0:25:01 > 0:25:03The dinosaurs vanished.
0:25:07 > 0:25:12Scientists spent years scrutinising dinosaur bones, looking for answers.
0:25:12 > 0:25:16- You got something? - Yeah, this is a vertebrae...
0:25:18 > 0:25:22They struggled to come up with ideas to explain the mass extinction.
0:25:22 > 0:25:25Perhaps the climate deteriorated, becoming too hot...
0:25:31 > 0:25:32..or too cold.
0:25:34 > 0:25:37Or suddenly too wet...
0:25:39 > 0:25:40..or too dry.
0:25:45 > 0:25:48There were problems maybe of reproduction
0:25:48 > 0:25:51or maybe their eggs were eaten by the tiny furry mammals.
0:25:56 > 0:25:57IT BURPS
0:26:00 > 0:26:04Maybe it was God's will or lack of standing room in the ark.
0:26:10 > 0:26:13But it was only when they turned their attention to rocks,
0:26:13 > 0:26:17rather than bones, that scientists had a breakthrough.
0:26:18 > 0:26:23Geologists searching for clues to the extinction discovered
0:26:23 > 0:26:26an unusual layer of clay in the geological record that marked
0:26:26 > 0:26:31the boundary between the time of the dinosaurs and the time of mammals.
0:26:31 > 0:26:35Nobel prize winning physicist Luiz Alvarez and his team
0:26:35 > 0:26:37took up the challenge.
0:26:38 > 0:26:41You see this clay layer here, about a half-inch thick.
0:26:41 > 0:26:43That's when the dinosaurs went out.
0:26:43 > 0:26:47We really don't know how long it took, why it's there.
0:26:47 > 0:26:51So I said, "Maybe some of the tricks I know as a physicist
0:26:51 > 0:26:54"might help unravel that story."
0:26:54 > 0:26:58And we talked about it for the next couple of weeks
0:26:58 > 0:27:01and finally decided to look for iridium
0:27:01 > 0:27:05as a measure of the deposition rate.
0:27:08 > 0:27:10A small quantity of the metal iridium
0:27:10 > 0:27:13constantly falls to Earth from space,
0:27:13 > 0:27:16and the team expected to find only trace amounts.
0:27:17 > 0:27:20But their tests showed something astonishing.
0:27:20 > 0:27:23There was so much iridium in the clay layer
0:27:23 > 0:27:26there could only be one source.
0:27:28 > 0:27:32Alvarez's radical idea was that it had been brought to Earth
0:27:32 > 0:27:33by a meteorite.
0:27:36 > 0:27:40The vast majority of iridium-bearing meteorites started life as asteroids.
0:27:40 > 0:27:43Most of them, in an orbit between Mars and Jupiter,
0:27:43 > 0:27:45never come anywhere near the Earth.
0:27:45 > 0:27:48But the theory goes that a few are occasionally
0:27:48 > 0:27:52swung out of line by the enormous gravitational pull of Jupiter.
0:27:54 > 0:27:58A very few of these finish up in an orbit which crosses the Earth's.
0:27:58 > 0:28:02Most of time they pass harmlessly by, but every now and then, they collide.
0:28:04 > 0:28:08Alvarez's theory is that 65 million years ago a huge asteroid,
0:28:08 > 0:28:12six miles wide, smashed into the Earth with devastating effects.
0:28:19 > 0:28:23It was this collision, he believes, that covered the Earth with iridium
0:28:23 > 0:28:26and wiped out the dinosaurs.
0:28:26 > 0:28:27It's not all that far-fetched.
0:28:27 > 0:28:29Only 25,000 years ago,
0:28:29 > 0:28:33a much smaller collision caused Meteor Crater in Arizona.
0:28:34 > 0:28:37There are larger impact craters on the Earth's surface.
0:28:37 > 0:28:40Many have been eroded away over time,
0:28:40 > 0:28:43and are rather difficult to recognise.
0:28:43 > 0:28:46Nevertheless, so far, over the whole world, more than 200
0:28:46 > 0:28:47have been identified,
0:28:47 > 0:28:52but none of these is both the right age and size for Alvarez's theory.
0:28:52 > 0:28:54However, there's an alternative.
0:28:54 > 0:28:56The asteroid may have landed in the sea.
0:28:56 > 0:28:58Dr Cesare Emiliani.
0:28:58 > 0:29:00We have no evidence at all
0:29:00 > 0:29:04of a crater of the size that this asteroid this should have made
0:29:04 > 0:29:07either on land or on the ocean floor.
0:29:07 > 0:29:10This is a map that shows the structure of the ocean floor.
0:29:10 > 0:29:11On the other hand,
0:29:11 > 0:29:15we have evidence indicating that plant life on the continents,
0:29:15 > 0:29:20in a broad area ranging from the Urals to the Rockies,
0:29:20 > 0:29:24suffered somewhat, at the end of the Cretaceous.
0:29:24 > 0:29:29While plant life west of the Urals, from the Urals to the Rockies,
0:29:29 > 0:29:31around the North Atlantic,
0:29:31 > 0:29:33suffered very little or nothing at all.
0:29:33 > 0:29:38That would seem to indicate that the point of impact of the asteroid
0:29:38 > 0:29:41was somewhere between the Urals and the Rockies.
0:29:41 > 0:29:45We have no crater on land, we have no crater on the visible ocean floor
0:29:45 > 0:29:50but a portion of the ocean floor since then has disappeared under the continent.
0:29:50 > 0:29:54Because the oceanic crust moves towards the continents
0:29:54 > 0:29:56and then dives under the continents.
0:29:56 > 0:29:59There is a substantial chance that the asteroid
0:29:59 > 0:30:02might have hit an area of the ocean floor
0:30:02 > 0:30:04that has since disappeared.
0:30:04 > 0:30:08If one were to make a wild guess as to where the asteroid may have hit,
0:30:08 > 0:30:11one would say somewhere in the North Pacific, round here.
0:30:15 > 0:30:19Without finding a crater, it was hard to prove that it was
0:30:19 > 0:30:21an asteroid that had killed off the dinosaurs.
0:30:26 > 0:30:29But, by 1997, scientists realised
0:30:29 > 0:30:32they'd been looking in the wrong place.
0:30:32 > 0:30:36A number of circular structures had been found in the Caribbean.
0:30:36 > 0:30:41The shape of islands, circular structures on the sea floor,
0:30:41 > 0:30:43circular geophysical anomalies.
0:30:43 > 0:30:47When you're looking for an impact crater, usually the obvious thing,
0:30:47 > 0:30:50because most craters are round, is looking for something big and round.
0:30:52 > 0:30:57One of Hildebrand's suspects was on the Yucatan peninsula of Mexico.
0:30:57 > 0:31:01There the state oil company, Petrolinas Mexicana, had detected
0:31:01 > 0:31:04a strange circular anomaly in the Earth's gravity field.
0:31:11 > 0:31:14Chixulub, the dead centre of the big round hole,
0:31:14 > 0:31:19but at the surface there's no sign of a catastrophe.
0:31:28 > 0:31:32The 200km-wide crater is hidden.
0:31:32 > 0:31:35It's buried hundreds of metres beneath the Earth's surface,
0:31:35 > 0:31:39so Hildebrand had to investigate it in some other way.
0:31:39 > 0:31:43We've taken another 1,400 measurements and combined them with the data that
0:31:43 > 0:31:48Petroleos Mexicanos already had to make this map of the gravity field.
0:31:48 > 0:31:52Here you can see all this concentric circular structure
0:31:52 > 0:31:55that represents the crater.
0:31:55 > 0:31:59From here to here is about 180km.
0:31:59 > 0:32:03Petroleos Mexicanos had known about this big buried structure for decades.
0:32:03 > 0:32:08They'd drilled several wells into it for oil exploration, beginning in 1952.
0:32:10 > 0:32:13When they did so, they found what they thought was volcanic rock.
0:32:13 > 0:32:17But this contains shock quartz and impact glass and so on.
0:32:17 > 0:32:20These are the classic signs,
0:32:20 > 0:32:23the deposits you'd expect in a big impact crater.
0:32:23 > 0:32:27The rock proved to be precisely 65 million years old -
0:32:27 > 0:32:29the age of the mass extinction.
0:32:29 > 0:32:34Here at last was the first confirmation that Chicxulub was ground zero.
0:32:36 > 0:32:41Hildebrand confirmed the theory proposed 17 years earlier
0:32:41 > 0:32:46that a devastating asteroid had hit Earth 65 million years ago.
0:32:53 > 0:32:57By 2004, scientists believed they had proof that the impact
0:32:57 > 0:33:00had caused a massive explosion...
0:33:02 > 0:33:08..quickly followed by an enormous shock wave that had destroyed life for hundreds of miles around
0:33:19 > 0:33:23And there was more. Investigations of the layer of rock
0:33:23 > 0:33:26that marks the time when the dinosaurs disappeared -
0:33:26 > 0:33:28known as the KT boundary -
0:33:28 > 0:33:33revealed further evidence of what had happened in the aftermath.
0:33:33 > 0:33:35These are called spherals.
0:33:35 > 0:33:39They're actually made of round rock globules, so we know they're condensed
0:33:39 > 0:33:46from a very hot vapour cloud. And some of the mineralogy in there
0:33:46 > 0:33:51tells us these globules originated at very high temperatures.
0:33:52 > 0:33:53That's exciting.
0:33:53 > 0:33:57You know something hot happened and hot is associated with an impact.
0:34:00 > 0:34:04The spherals were evidence that the fireball had vaporised
0:34:04 > 0:34:07billions of tons of rock.
0:34:07 > 0:34:11In outer space, the vapour condensed into tiny droplets which fell back
0:34:11 > 0:34:15all over the Earth as white hot spherals.
0:34:20 > 0:34:24From America to New Zealand there seemed to be
0:34:24 > 0:34:28evidence of massive burning at time of impact.
0:34:28 > 0:34:31It looked as if the world's forests had spontaneously ignited,
0:34:31 > 0:34:36as the spherals heated the atmosphere by up to 1,000 degrees centigrade.
0:34:38 > 0:34:42If we're looking at 600, 1,000 degrees, then this would instantly
0:34:42 > 0:34:45have ignited all the plant matter across the world
0:34:45 > 0:34:51and it just would have been sent up in flames.
0:34:51 > 0:34:57The impact was also thought to have created vicious acid rain.
0:34:59 > 0:35:03The fireball had release chemicals, which turned the water deadly.
0:35:05 > 0:35:08It was suggested that the acid rain had a pH
0:35:08 > 0:35:10so low it was like battery acid.
0:35:10 > 0:35:12If you had something that low,
0:35:12 > 0:35:15it would literally burn everything on the land
0:35:15 > 0:35:18from plants, to dinosaurs to everything else.
0:35:19 > 0:35:23Then there was the final clue from the KT boundary -
0:35:23 > 0:35:26a high concentration of fern spores.
0:35:31 > 0:35:37Ferns flourish whenever all other plants have been killed off by some environmental devastation.
0:35:39 > 0:35:44So the predominance of fern spores - known as a fern spike -
0:35:44 > 0:35:48suggested something had wiped out every plant on the planet.
0:35:51 > 0:35:55Fern spikes were found all over the world, such as in New Zealand.
0:35:55 > 0:35:57This, I think, became stronger and stronger evidence
0:35:57 > 0:36:01that there was something LIKE global darkness caused by an impact.
0:36:04 > 0:36:08So the theory grew up that vast amounts of dust created by the impact
0:36:08 > 0:36:10must have blocked out the sun.
0:36:11 > 0:36:17This could have plunged the world into freezing darkness for months or years.
0:36:19 > 0:36:24Any dinosaurs that escaped burning either froze or starved to death.
0:36:34 > 0:36:37The mystery surrounding the death of the dinosaurs
0:36:37 > 0:36:41finally appeared to have been solved.
0:36:43 > 0:36:46A number of factors may have influenced the extinction,
0:36:46 > 0:36:51but research had shown that the impact at Chicxulub WAS the crucial factor.
0:36:59 > 0:37:02We should probably be thankful for that mighty asteroid -
0:37:02 > 0:37:05if the dinosaurs hadn't been wiped out,
0:37:05 > 0:37:08mammals may never have flourished and we might not exist.
0:37:08 > 0:37:11So what would have happened if an asteroid hadn't hit the Earth
0:37:11 > 0:37:14and the dinosaurs had survived?
0:37:14 > 0:37:18It's a thought that's given rise to some novel ideas.
0:37:18 > 0:37:22I think that some dinosaurs, like some mammals would have become
0:37:22 > 0:37:25increasingly intelligent at a geometric rate,
0:37:25 > 0:37:26as did our own ancestors,
0:37:26 > 0:37:30and I think, possibly, by this time the dinosaurs themselves
0:37:30 > 0:37:34would have approached our own level of brain development.
0:37:34 > 0:37:36A sculptor at our museum
0:37:36 > 0:37:39and myself have collaborated over the last several months in trying
0:37:39 > 0:37:43to estimate what the appearance of one of these highly encephalised
0:37:43 > 0:37:46or intelligent dinosaurs might have been, a dinosaur for the 1980s,
0:37:46 > 0:37:50and here is an example of what we think it may have looked like.
0:37:56 > 0:37:59Their model of a 20th-century dinosaur incorporates
0:37:59 > 0:38:03many features of the original reptiles - the binocular vision,
0:38:03 > 0:38:08the absence of an external ear, a deep chest cavity with ribs
0:38:08 > 0:38:10all the way down the abdomen,
0:38:10 > 0:38:13opposable fingers and no external genitalia.
0:38:13 > 0:38:16But it looks closer to a human being than a brontosaurus.
0:38:16 > 0:38:20In building it, have they perhaps unwittingly favoured our own kind?
0:38:20 > 0:38:21I don't think so.
0:38:21 > 0:38:26I think just as the birds, bats and flying reptiles all have
0:38:26 > 0:38:31a crudely avian form, so too there is a meaning to the human form.
0:38:31 > 0:38:34So that we are, in effect, adapted to interact with
0:38:34 > 0:38:38an environment as highly encephalised bipeds
0:38:38 > 0:38:41or walking animals with a very large brain.
0:38:41 > 0:38:45So perhaps were it not for a chance collision with an asteroid,
0:38:45 > 0:38:48creatures like this could be ruling the world today
0:38:48 > 0:38:51just as they did all those millions of years ago.
0:38:53 > 0:38:56Let's imagine that the dinosaurs really did become some sort
0:38:56 > 0:38:59of dinosauroid, the great rock doesn't fall out of the sky,
0:38:59 > 0:39:02there's a bright light in the sky, the dinosaur says, "What's that?
0:39:02 > 0:39:07"No idea". The mass extinction is postponed. In fact, cancelled.
0:39:07 > 0:39:08So what's happening then?
0:39:08 > 0:39:11We've got the Apes rapidly evolving and they're beginning to
0:39:11 > 0:39:14look over their shoulders because just conceivably there are also
0:39:14 > 0:39:18these dinosauroids doing rather similar things.
0:39:18 > 0:39:20What would have happened?
0:39:20 > 0:39:24Would it have been an evolutionary race? Maybe there would have been a winner?
0:39:24 > 0:39:29Or maybe, unbelievably, madly, there could have been a co-operation.
0:39:31 > 0:39:36The Utopian notion of dinosaurs and humans sharing the planet may appeal,
0:39:36 > 0:39:38even be plausible to some,
0:39:38 > 0:39:43but most palaeontologists see the dinosauroid as an insult to dinosaurs.
0:39:43 > 0:39:45There's probably some good ideas there.
0:39:45 > 0:39:48The brain was getting bigger, and they probably
0:39:48 > 0:39:51would have continued to outcompete other animals.
0:39:53 > 0:39:58But for them to become fully erect like humans is a little bit fanciful.
0:40:00 > 0:40:03Dinosaurs would have continued to develop, to specialise.
0:40:03 > 0:40:07They would have adapted, but they would have adapted
0:40:07 > 0:40:11and specialised as dinosaurs, they wouldn't have become primate-like.
0:40:11 > 0:40:16The idea that a dinosauroid could exist as a scientific question...
0:40:16 > 0:40:19is bogus. It's about as bogus as it gets.
0:40:19 > 0:40:25It is fairly arrogant to think the endpoint of evolution
0:40:25 > 0:40:28should emulate human beings.
0:40:32 > 0:40:34If the asteroid had never hit,
0:40:34 > 0:40:38life on Earth could have been very different.
0:40:52 > 0:40:55But that's all just crazy speculation.
0:40:55 > 0:40:59Everyone now knows that dinosaurs were wiped out 65 million years ago
0:40:59 > 0:41:03and none of them survived that catastrophic asteroid impact.
0:41:03 > 0:41:04Or did they?
0:41:04 > 0:41:07The idea that dinosaurs may have evolved into something else
0:41:07 > 0:41:10was one that had been doing the rounds for many years.
0:41:10 > 0:41:13But it began to gather momentum when some palaeontologists
0:41:13 > 0:41:18began to increasingly suspect that dinosaurs might still be alive.
0:41:34 > 0:41:40The Natural History Museum, London. Within these hallowed halls
0:41:40 > 0:41:43lies the fossil that first hinted at the origin of birds.
0:41:43 > 0:41:47Discovered in Germany 100 ago,
0:41:47 > 0:41:50superstitious quarry workers thought it was a fallen angel.
0:41:58 > 0:42:02Archaeopteryx turned out to be something almost as remarkable.
0:42:02 > 0:42:06The size of a pigeon, it possessed teeth, a long, bony tail,
0:42:06 > 0:42:11and claws on its arms. All features of reptiles.
0:42:11 > 0:42:14At the same time, it was very much like a bird.
0:42:16 > 0:42:20It actually has impressions of the wing feathers, both wings
0:42:20 > 0:42:25and long tail feathers, but the tail has a long set of bones
0:42:25 > 0:42:29running down it as well, which modern birds don't have at all.
0:42:29 > 0:42:33So Archaeopteryx really does seem to be a primitive bird.
0:42:34 > 0:42:37These fossils, I find it exciting to look at them
0:42:37 > 0:42:41because they have so much scientific information in them,
0:42:41 > 0:42:45but they're very beautiful objects to look at in their own right.
0:42:45 > 0:42:49They really are an exceptional snapshot record of evolution.
0:42:55 > 0:42:58That fossil was to be the key to something that John Ostrom
0:42:58 > 0:43:01had been thinking about for decades.
0:43:02 > 0:43:05When he'd first described Deinonychus in the 1960s,
0:43:05 > 0:43:10he'd noticed that its skeleton was strangely similar to that of a bird.
0:43:12 > 0:43:16Archaeopteryx helped him refine his ideas.
0:43:16 > 0:43:18Neat animal, isn't it?
0:43:20 > 0:43:22I think so.
0:43:22 > 0:43:25And what made me even more excited
0:43:25 > 0:43:28was when I saw structures in that animal
0:43:28 > 0:43:30that I subsequently recognised
0:43:30 > 0:43:33in Archaeopteryx.
0:43:33 > 0:43:38- This is the Solnhofen Archaeopteryx. - The Solnhofen specimen, yeah.
0:43:40 > 0:43:43John Ostrom's crucial realisation was that
0:43:43 > 0:43:49his beloved Deinonychus shared many anatomical features with Archaeopteryx.
0:43:49 > 0:43:53He compared in detail the skeletons of predatory dinosaurs,
0:43:53 > 0:43:55Archaeopteryx and modern birds.
0:43:55 > 0:44:00He found a whole set of similarities - most notably in the skull,
0:44:00 > 0:44:02the hind limbs and the forearms.
0:44:02 > 0:44:07For a start, they all have the same number of fingers.
0:44:07 > 0:44:10This is the skeleton of a modern pigeon.
0:44:10 > 0:44:13Three fingers in the hand of a modern bird,
0:44:13 > 0:44:18three fingers preserved in the hand of Deinonychus, and that particular
0:44:18 > 0:44:23kind of hand morphology is also supplemented by
0:44:23 > 0:44:28the strange wrist bone that allows for the flexibility
0:44:28 > 0:44:30that produces the flapping strokes.
0:44:30 > 0:44:34The similarities between birds
0:44:34 > 0:44:39and predaceous dinosaurs is amazing to me.
0:44:41 > 0:44:44But, as with all groundbreaking new theories,
0:44:44 > 0:44:47Ostrom's idea had its detractors.
0:44:49 > 0:44:53The dinosaur-bird theory has tremendous popular appeal,
0:44:53 > 0:44:58one can vicariously study dinosaurs at the back yard bird feeder,
0:44:58 > 0:45:04and one can buy a piece of dinosaur leg at the local Kentucky Fried Chicken.
0:45:04 > 0:45:08So it has tremendous appeal to the public.
0:45:08 > 0:45:10Unfortunately, it seems to be wrong.
0:45:12 > 0:45:17Alan Feduccia argued that birds evolved long before dinosaurs came along.
0:45:17 > 0:45:20They descended from much more primitive reptiles,
0:45:20 > 0:45:24and any similarity between birds and predatory dinosaurs was superficial.
0:45:24 > 0:45:29They resembled each other because they both walked on their hind legs,
0:45:29 > 0:45:32not because they were closely related.
0:45:36 > 0:45:39Such vocal sceptics were going to need better proof
0:45:39 > 0:45:43if they were to be convinced of the dinosaur-to-bird theory.
0:45:50 > 0:45:54And in 1999 in Tucson, Arizona, fossil collectors thought
0:45:54 > 0:45:58they might have come across a specimen that fitted the bill.
0:46:04 > 0:46:07I carried it out to the light
0:46:07 > 0:46:11of the sunlight so that I could see it cross lit.
0:46:14 > 0:46:18And there were a number of beautiful teeth in this skull.
0:46:18 > 0:46:20And that was very exciting.
0:46:20 > 0:46:25And then we studied also the tail that was a dinosaur...
0:46:25 > 0:46:27a very dinosaur-like tail.
0:46:27 > 0:46:30I got this incredible high feeling,
0:46:30 > 0:46:33the feeling of discovery - that wonderful time
0:46:33 > 0:46:36when everything clicks into position.
0:46:38 > 0:46:41The two fossil dealers thought they could be looking at
0:46:41 > 0:46:44one of the most important fossils ever found.
0:46:44 > 0:46:46A specimen that would prove beyond doubt
0:46:46 > 0:46:51one of the most controversial theories in all of evolution.
0:46:51 > 0:46:55This fossil, this clearly cross between a bird
0:46:55 > 0:47:00and a dinosaur was what everybody had been looking for.
0:47:00 > 0:47:02And here it was, right there, right in front of my eyes,
0:47:02 > 0:47:04and I was one of the first people to see it.
0:47:07 > 0:47:08I looked it over very carefully.
0:47:08 > 0:47:10Literally under a magnifying glass.
0:47:10 > 0:47:14And I was looking for any tell-tale features, particularly on the tail.
0:47:14 > 0:47:16I wanted to look at that tail very carefully
0:47:16 > 0:47:20because it was very clearly a dinosaur tail.
0:47:22 > 0:47:25The world of palaeontology was gripped
0:47:25 > 0:47:28and a team of experts was assembled to investigate.
0:47:35 > 0:47:39After several months, they confirmed that it was the missing link.
0:47:39 > 0:47:43It had a bird-like front and legs, and a dinosaur-like tail.
0:47:47 > 0:47:49They called it Archaeoraptor,
0:47:49 > 0:47:50ancient hunter,
0:47:50 > 0:47:53and proudly presented it to the world.
0:47:56 > 0:48:00Scientists could now say that dinosaurs evolved into birds.
0:48:00 > 0:48:04One of the most important theories in evolution was finally proved.
0:48:10 > 0:48:12But not everyone was convinced.
0:48:20 > 0:48:24At the university of Texas, Tim Rowe had used a CAT scan
0:48:24 > 0:48:26to study the fossil.
0:48:26 > 0:48:31The results threw up some serious questions about how it fitted together.
0:48:31 > 0:48:33I'm going to show you two slices.
0:48:33 > 0:48:35The first is this slice here through the skull
0:48:35 > 0:48:38and these other elements here,
0:48:38 > 0:48:41and the second slice will be back through the ankle and tail,
0:48:41 > 0:48:44this critical region here through one of the legs.
0:48:46 > 0:48:49When we go to these slices, here's what we see.
0:48:49 > 0:48:51Here's the skull.
0:48:51 > 0:48:55We can see the skull is part of this upper layer of shale.
0:48:56 > 0:48:59And you can see the fracture pattern here,
0:48:59 > 0:49:01here's very tight fractures that fit together.
0:49:01 > 0:49:05Here, a pair of fractures, one occurring against the next.
0:49:05 > 0:49:06A straight fracture.
0:49:06 > 0:49:10The pieces on either side are the same thickness. Same density.
0:49:10 > 0:49:12But when we get to the edge of the block,
0:49:12 > 0:49:14this piece is a little bit thicker
0:49:14 > 0:49:18and denser than the piece it's glued against.
0:49:19 > 0:49:22As we move to the tail, to the critical area,
0:49:22 > 0:49:25we can see that it's completely surrounded by grout,
0:49:25 > 0:49:29and that there are no natural ties between the tail piece
0:49:29 > 0:49:32and this piece to the right or left.
0:49:32 > 0:49:35In fact, it's just swimming in this ocean of grout here.
0:49:35 > 0:49:40And as we map through the entire specimen, we found no verifiable fits
0:49:40 > 0:49:44between the tail and any of the other parts anywhere else in the specimen.
0:49:49 > 0:49:53The scan clearly showed what the naked eye couldn't see.
0:49:53 > 0:49:57There was no natural skeletal link between the all-important tail
0:49:57 > 0:49:59and the rest of the fossil.
0:50:00 > 0:50:04It had simply been glued on with grout.
0:50:10 > 0:50:13The vital evidence that seemed to prove the link between birds
0:50:13 > 0:50:15and dinosaurs was a fake.
0:50:21 > 0:50:26The dinosaur fake was a dreadful blow for supporters of the bird theory.
0:50:26 > 0:50:29But scientists who were committed to the idea refused to give up.
0:50:29 > 0:50:33They were determined to keep looking for proof.
0:50:35 > 0:50:37Although the fossil had been a fake,
0:50:37 > 0:50:41its front half was a new kind of primitive bird.
0:50:43 > 0:50:47Fossil hunters flocked to the region where it had been found.
0:50:47 > 0:50:49And they struck gold.
0:50:58 > 0:51:02Extraordinary, well preserved fossils revealed dinosaurs
0:51:02 > 0:51:05and birds not only shared features like downy feathers,
0:51:05 > 0:51:10but also hollow bones and similar pelvises and hind limbs.
0:51:27 > 0:51:30On a remote farm in Colorado,
0:51:30 > 0:51:33palaeontologist Brent Breithaupt presented even more proof
0:51:33 > 0:51:37of the close relationship between the ancient fossils and birds.
0:51:40 > 0:51:43Very good. That should make an excellent track.
0:51:43 > 0:51:48Here we have two tracks that we recently made.
0:51:48 > 0:51:51This one here is from the Red Gulch Dinosaur Tracksite.
0:51:51 > 0:51:56This one here preserves the three-toe impressions,
0:51:56 > 0:52:00tridactyl impressions, of the foot of the dinosaurs.
0:52:00 > 0:52:03The small to medium sized theropod dinosaurs that lived up there.
0:52:03 > 0:52:10Now, over here, we have one that we just got from this site.
0:52:10 > 0:52:14Again, a nice tridactyl footprint.
0:52:14 > 0:52:16Again, very well preserved.
0:52:16 > 0:52:19If we compare both casts,
0:52:19 > 0:52:24we can see these particular tracks look very, very much the same.
0:52:25 > 0:52:30But these footprints are not of a theropod that died 65 million years ago...
0:52:32 > 0:52:34These are only a few hours old.
0:52:37 > 0:52:39There's dinosaurs in them there hills.
0:52:42 > 0:52:45In fact, dinosaurs are everywhere.
0:52:54 > 0:52:57For the first time on network television,
0:52:57 > 0:53:03palaeontologist Julia Clarke is about to perform an autopsy on a dinosaur.
0:53:05 > 0:53:09Only you are more likely to know it...
0:53:09 > 0:53:11as a roast turkey.
0:53:13 > 0:53:17Because you see, birds ARE dinosaurs.
0:53:17 > 0:53:21So today we're going to dissect the evidence that birds
0:53:21 > 0:53:24are living dinosaurs from this turkey.
0:53:27 > 0:53:30What we're pulling off here is the major flight muscle,
0:53:30 > 0:53:35supracoracoideus that is in velociraptor and oviraptor.
0:53:37 > 0:53:41One of the features you see is that the second finger is the longest.
0:53:41 > 0:53:46This is a feature we see going back as far as early dinosaurs,
0:53:46 > 0:53:48even Triassic forms.
0:53:54 > 0:53:59We're all familiar with wishbones, from any kind of turkey meal.
0:53:59 > 0:54:04Wishbones actually are one of the most intuitive pieces of evidence
0:54:04 > 0:54:08that birds are living dinosaurs, because we have wishbones now
0:54:08 > 0:54:13from a variety of theropod dinosaurs, including relatives of tyrannosaurus
0:54:13 > 0:54:18and velociraptor, and even earlier dinosaurs such as coelophysis.
0:54:22 > 0:54:27Yes, just as we share 98% of our DNA with chimps,
0:54:27 > 0:54:31turkeys - in fact all modern birds -
0:54:31 > 0:54:34are direct descendants of theropod dinosaurs.
0:54:44 > 0:54:49And the freshly-made dinosaur tracks in the hills of Colorado?
0:54:51 > 0:54:52Emus.
0:54:55 > 0:54:58Inwardly, outwardly, even in the way they move,
0:54:58 > 0:55:03the similarities between theropod dinosaurs and birds are numerous.
0:55:03 > 0:55:07But, being warm-blooded, their ultimate success
0:55:07 > 0:55:11was in an evolutionary solution to the need to keep warm.
0:55:11 > 0:55:15Large dinosaurs really don't have a problem with body heat.
0:55:15 > 0:55:19If they have a problem, it's getting rid of excess body heat.
0:55:19 > 0:55:21But small dinosaurs have this problem.
0:55:21 > 0:55:23They're losing their heat all the time.
0:55:23 > 0:55:26So it would be a good thing if a small dinosaur was
0:55:26 > 0:55:30warm-blooded, for it to have some kind of insulation on its body.
0:55:30 > 0:55:35It started with the development of thin, downy filaments.
0:55:35 > 0:55:39In time, those filaments strengthened and thickened.
0:55:39 > 0:55:44As non-flying birds, emus are one of the best examples
0:55:44 > 0:55:48of feathers as they were originally designed. As an insulating layer.
0:55:49 > 0:55:53Once you have those long feathers, then of course it does give you
0:55:53 > 0:55:55an aerodynamic advantage as well.
0:55:55 > 0:56:00And if you have that advantage, then selection starts working on that advantage.
0:56:00 > 0:56:04And it may well be that that was forcing these feathers to become longer
0:56:04 > 0:56:08and longer until finally that animal not only jumped across the ditch,
0:56:08 > 0:56:11it actually flapped its arms and flew across the ditch.
0:56:11 > 0:56:13And so it seems that flight, far from being
0:56:13 > 0:56:19the reason for the evolution of feathers, may have been a by-product.
0:56:19 > 0:56:22But with it, some dinosaurs were already adapting in ways
0:56:22 > 0:56:26that would equip them for life after the meteorite impact.
0:56:28 > 0:56:32The fact of the matter is that the age of the dinosaurs never actually ended.
0:56:32 > 0:56:37Dinosaurs DID survive the cataclysmic event of 65 million years ago.
0:56:40 > 0:56:44So when we talk about dinosaurs living with us today,
0:56:44 > 0:56:49and the fanciful notion of what it would be like, it's not so much fantasy.
0:56:49 > 0:56:50They're right there.
0:56:50 > 0:56:54Dinosaurs have not only survived, there are far more species of them
0:56:54 > 0:56:59- on the Earth today than there are mammals.- They're not the biggest animals any more,
0:56:59 > 0:57:03but still there's over 10,000 living species of descendents of dinosaurs.
0:57:03 > 0:57:07They didn't actually go extinct at the end of the Cretaceous period
0:57:07 > 0:57:10like everybody thinks. They're outside flying around.
0:57:10 > 0:57:14You can't go into a forest without hearing dinosaurs.
0:57:14 > 0:57:18In that sense, maybe they won out,
0:57:18 > 0:57:21and we just think we're on top.
0:57:26 > 0:57:29Over the last half-century,
0:57:29 > 0:57:33scientists have hunted all over the world for new clues
0:57:33 > 0:57:38to help them piece together the fragments which reveal the life of the dinosaurs.
0:57:38 > 0:57:41They've come up with ingenious new ways of working out
0:57:41 > 0:57:45how the dinosaurs lived and behaved,
0:57:45 > 0:57:49made extraordinary discoveries,
0:57:49 > 0:57:55and battled to answer some of the oldest, most vital questions of all.
0:57:59 > 0:58:02But there are still things we don't know,
0:58:02 > 0:58:05mysteries to be solved, and one of the exciting things
0:58:05 > 0:58:07about palaeontology is that, in an instant,
0:58:07 > 0:58:10perhaps with just the tiniest of discoveries,
0:58:10 > 0:58:13everything we think we know about dinosaurs today
0:58:13 > 0:58:14could all change again.
0:58:14 > 0:58:17There are always new discoveries out there...
0:58:17 > 0:58:18waiting to be found.
0:58:34 > 0:58:38Subtitles by Red Bee Media Ltd
0:58:38 > 0:58:41Email subtitling@bbc.co.uk