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Documentary, David Attenborough - Dinosaurs - The Final Day
##AncientEarth #Documentary #Dinosaurs #Prehistoric
##AncientEarth #Documentary #Dinosaurs #Prehistoric
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AnimalsTranscript
00:00:0066 million years ago, planet Earth was very different from today.
00:00:20Back then, one of our closest ancestors
00:00:23might have looked something like this little furry creature.
00:00:30The rulers of the land were giant reptiles.
00:01:00Dinosaurs. That's one of the most infamous, a carnivorous T-Rex.
00:01:13And just behind are the bison of that time, a common plant-eater, Edmontosaurus.
00:01:19But what happened to them all?
00:01:2466 million years ago, an asteroid hit the Earth.
00:01:28And scientists think that it was this collision that wiped out the dinosaurs.
00:01:34But no one has ever found direct evidence of that.
00:01:38In fact, no one has ever found the fossil of a dinosaur
00:01:42that died within a thousand years of the impact.
00:01:45However, a remarkable dig site promises to change that.
00:01:56It's in the Hell Creek Formation in the American Midwest.
00:02:00These badlands are rich in prehistoric remains.
00:02:07From Triceratops
00:02:11To Pterosaurs.
00:02:17And here, one patch of land about the size of a football pitch
00:02:22is yielding a collection of astonishing fossils.
00:02:29The precise location is a closely guarded secret
00:02:33because this place may hold evidence
00:02:38of one of the most dramatic events
00:02:40in all the four and a half billion year history of our planet.
00:02:44All right, we'll get down here between you.
00:02:51For ten years, a paleontologist and his team
00:02:54have been trying to find out exactly what happened here.
00:02:58You're at the edge of your seat every moment
00:03:00trying to dig this stuff up.
00:03:02It's like trying to defuse a nuclear weapon
00:03:03while you're in a rainstorm.
00:03:06He's named the site Tanis
00:03:08and believes it could be a mass graveyard of creatures
00:03:11that were killed in the catastrophic asteroid strike.
00:03:20A site that could reveal not only how the last dinosaurs lived
00:03:25but how they died.
00:03:28If the dig team is right,
00:03:31Tanis could be a place
00:03:33where the remains of a long lost world
00:03:36are frozen in time.
00:03:37A place that gives us, for the first time,
00:03:42an unprecedented window
00:03:47into the lives of the very last dinosaurs.
00:03:55And a minute-by-minute picture of what happened
00:03:58on the day the asteroid hit.
00:04:00This landscape is full of fossils dating from the late Cretaceous.
00:04:14The period which began around a hundred million years ago
00:04:18and ended 66 million years ago when the dinosaurs vanished.
00:04:35Paleontologist Robert De Palma wants to find out more.
00:04:40I think anybody who has ever liked dinosaurs in the past,
00:04:45or still does, has thought at one point or another,
00:04:49well, what happened to them?
00:04:50Why are they not here anymore?
00:04:52So many different theories are out there
00:04:54and nobody has a tight answer to that question.
00:05:02Judging from fossil evidence,
00:05:03this is what Hell Creek looked like in the late Cretaceous.
00:05:14There were low-lying marshy floodplains
00:05:17intercut by river channels
00:05:19and covered with horsetails, ferns and trees.
00:05:23Back then, it was warm and wet here all year round.
00:05:27Tannis lies in the north-eastern corner of the Hell Creek Formation.
00:05:38Instead of today's dusty prairies, there were sandy riverbanks.
00:05:45Instead of rocky cliffs, there were forests.
00:05:50And instead of the life we know today...
00:05:52Well, Robert is hoping to find out more about what that was like.
00:06:07A sandbank lying between a river and a forest
00:06:12would one day become what Robert now calls Tannis.
00:06:16He and his team have been digging here since 2012.
00:06:23So, somewhere from between there and down here is where that came from.
00:06:28Hey, look at that.
00:06:30What?
00:06:32Oh, yeah, yeah, yeah, okay.
00:06:34And what they found is unexpected.
00:06:36Here we've got this freshwater environment
00:06:39of the Hell Creek Formation
00:06:40and this shocking red-green color is coming from the shells of ammonites,
00:06:46a marine organism, kind of like a coiled snail in appearance.
00:06:50So, we've got this marine organism that's been thrown up
00:06:53into this freshwater environment, and they do not belong here.
00:06:57How they got here is a mystery.
00:07:01And there's more.
00:07:03I'm just going to go ahead and plane down some of this rock.
00:07:06Sitting just above the ammonites is something that many dinosaur hunters
00:07:12are desperate to find.
00:07:14So, this orange layer right here is composed 100% of impact-related debris
00:07:21that is enriched in iridium.
00:07:23Iridium is an element that's rare in the Earth's crust,
00:07:27but it's common in asteroids.
00:07:30The layer it's in is called the KPG boundary.
00:07:34It's made up of dust and debris from a huge asteroid impact.
00:07:46Look at that.
00:07:48That's me.
00:07:50Yeah, yeah, yeah, yeah, yeah.
00:07:51That's what we want.
00:07:52Okay, so it's coming from this area here.
00:07:53So, somewhere within that region is where these pieces are coming from.
00:07:56The boundary separates the age of the dinosaurs from the age of mammals.
00:07:59So, the rocks here come from about the time that the dinosaurs became extinct.
00:08:05No rattlesnakes.
00:08:07What makes the site even more exciting is the rock layer right beneath the boundary
00:08:13where Robert found the ammonites.
00:08:14The rock here is really not quite rocky as you would expect dinosaur bones and things to be encased.
00:08:20You'd expect really, really hard rocks and jackhammers and things like this, but it's very, very crumbly,
00:08:26and it just falls apart in your hands.
00:08:28As well as being crumbly throughout, this layer of rock is also around a metre thick, which, along with other unusual features,
00:08:39makes Robert think that something very strange must have happened here.
00:08:48Maybe a flood or a mud flow, burying anything within it in an instant.
00:08:53Oh, there's a beautiful. Look at that one. Beautiful.
00:08:57This could mean that anything he finds in this lair would have been quickly entombed,
00:09:03like the bodies in the volcanic ash of Pompeii.
00:09:06Robert knows from the geology that anything he finds at Tannis will be tantalizingly close to the end of the age of the dinosaurs,
00:09:21and could be so well preserved that it could reveal new evidence that would bring this time period to life in a way no one has ever done before.
00:09:31Robert digs at Tannis each summer, the only time the weather allows him to do so.
00:09:41Come on down. Check out this lens over here.
00:09:45In order to understand how the impact affected life on Earth, you really need to get a very clear picture of what the world was like right before.
00:09:55That is a critical part of the story.
00:09:57Paleontologists Dr. David Burnham and Lauren Goerche have been digging with Robert for years.
00:10:10Oh, wow. See the brown?
00:10:14Yep.
00:10:15That might be a tubercle right there.
00:10:17And it seems today is their lucky day.
00:10:20Oh, my God. Look at that. Look, the scales are preserved.
00:10:23It's like doing a freaking dissection.
00:10:26Oh, my God.
00:10:28Biology of Tannis.
00:10:30Oh, the scale. Look, look, the wrinkles continue down that way.
00:10:33It's all nice and wet so far.
00:10:36The scales are getting smaller in that direction. How big are they there?
00:10:39I got one with the projection over here.
00:10:42What?
00:10:44Yeah, there's the protuberance right there.
00:10:46I've only seen that on one other specimen.
00:10:47I want life.
00:10:48Yeah.
00:10:49This is the closest thing to getting the touch of a living, breeding dinosaur.
00:10:52It is.
00:10:54They found something extraordinary.
00:10:57It is so exceedingly rare, a piece of Triceratops skin in the Hell Creek Formation.
00:11:02It may look like an impression in the rock, but this is skin that has been fossilized.
00:11:11And over millions of years has turned to stone.
00:11:16Triceratops bones are relatively common finds in Hell Creek.
00:11:22But skin in such condition as this is very rare indeed.
00:11:27The size and the patterning of the scales, together with the age and location of the rocks where it was found, strongly suggests that this is from a Triceratops.
00:11:40The brown color contains traces of organic material, so it might even be possible from this to work out which pigments were in it.
00:11:50Finding and studying such well-preserved fossils as this helps paleontologists build a much more detailed picture of how these creatures lived.
00:12:03Combining this information with insights from scientists around the world makes it possible to speculate about what life in the late Cretaceous might have been like.
00:12:13We know from bones that adult Triceratops could reach 9 meters in length and 3 meters in height.
00:12:34Marks on the fossil also show us that this one was badly scarred.
00:12:38Triceratops were plant-eaters.
00:12:56Other fossils tell us that they had sharp beaks and hundreds of teeth that enabled them to shred tough plants such as these cycads.
00:13:04Almost all adult Triceratops fossils, including Robert's, have been found on their own.
00:13:22So it's possible that the adults were solitary, like modern-day male rhinos.
00:13:27So they were probably territorial, chasing rivals away.
00:13:36And perhaps marking their territories.
00:13:42If you weigh more than an African elephant, there's not much that can bother you.
00:13:52Except perhaps a little mammal.
00:13:53Robert found these jaw bones in the fossilised burrow.
00:13:54Robert found these jaw bones in the fossilised burrow.
00:13:55at Tannis.
00:13:56The shape of the jaw bones in the fossilised burrow.
00:13:57At Tannis.
00:13:58The shape of the jaw bones in the fossilised burrow.
00:13:59The shape of this tiny bone and tooth means it's most likely come from the fossilised burrow.
00:14:00Perhaps a little mammal.
00:14:02Perhaps a little mammal.
00:14:05Robert found these jaw bones in the fossilised burrow.
00:14:11The shape of this tiny bone and tooth means it's most likely come from what's known as a paidiomyid.
00:14:29from what's known as a pediomyid, an early mammal and a type of marsupial.
00:14:39Robert also discovered fossilized nuts and seeds in the burrow.
00:14:45So we have an idea about what it might have eaten.
00:14:48Robert's finds are adding to our knowledge of the complex world at the very end of the
00:15:02late Cretaceous. And it's not just the fossilized creatures. If you walk on damp sand, you'll
00:15:10leave a trace behind. A footprint. The same was true 66 million years ago. And very, very occasionally,
00:15:25such traces were preserved. And that's exactly what happened here at Tannis.
00:15:33You know, we won't foil a backside. Right. We'll just put plaster right on. Right on.
00:15:38Robert has discovered a number of footprints. Yeah. Let's see. Looks like a good print. Yeah.
00:15:50Their shape gives him a clue as to what might have made them.
00:16:00If he's right, they were made by a winged creature that might well have liked a small mammal.
00:16:07The footprints are long and narrow with four toe prints.
00:16:23Two are slightly longer than the others. And that suggests they were made by...
00:16:29The pterosaur.
00:16:43Pterosaurs are not dinosaurs, but flying reptiles on a different branch of the evolutionary tree.
00:16:49Male pterosaurs usually had crests, while females didn't. So crests may have been used in courtship displays.
00:17:12And we have an indication of where females laid their eggs. Because evidence suggests one pterosaur laid hers
00:17:29in the soft sandy banks in the soft sandy banks of the river at Tannis.
00:17:33And this is a fossilized egg of a pterosaur that Robert found there.
00:17:54The only one ever discovered in North America. If you look at it with the naked eye, all you see
00:18:03is a jumble of lines. But if you examine it with the latest technology, you can find out
00:18:11a wealth of information. From the chemistry of the bones to the composition of the shell.
00:18:17And that, in turn, can tell us a lot about how these incredible creatures lived.
00:18:29Robert has been given access to the diamond light source synchrotron in Oxfordshire.
00:18:35It's a very powerful research tool that acts like a giant microscope.
00:18:44By accelerating electrons in this huge ring,
00:18:47the synchrotron creates beams of light many times brighter than the sun.
00:18:52Robert and paleobiologist Dr. Victoria Egerton now want to turn that beam onto the egg fossil
00:19:06to discover more about its chemical makeup.
00:19:10We're pretty much lined up on the skeleton, but we might have to move the stage a little bit to get to
00:19:14the right part. Sure. Meanwhile, Robert can reveal the creature inside.
00:19:22And this, who made this wonderful thing? I got replicas of the bones from inside that egg,
00:19:31and I restored the remainder and put together what the skeleton would have looked like when it hatched.
00:19:36That's how big the creature would have been outside the egg, if it had hatched.
00:19:40So, this is the baby. How big was it going to grow?
00:19:45These very long neck vertebrae here are what really gave part of the story away to us,
00:19:50because those long bones match very, very closely with the Asdarkid pterosaurs.
00:19:55That is the giant pterosaurs. Oh, they were the whoppers, weren't they? I mean,
00:20:00what, 25 feet wingspan? Some of them.
00:20:04This probably had a wingspan maybe 15 feet, 5 meters.
00:20:09Well, it looks as though it could take off, really.
00:20:11It's easy to picture something like that, just hatching out of the egg and
00:20:14fluttering out almost like a little bat.
00:20:21They've scanned the egg here and in America.
00:20:28Victoria has the results.
00:20:30So, what have you learned from this cyclotron image?
00:20:36What we have here is a chemical map of calcium directly within the bones of this animal. That
00:20:42tells us that these bones were already hardened, so it might be ready to fly not long after it hatches.
00:20:49Okay. Can you see any sign of the shell? And what sort of shell was it?
00:20:54We can. What I can show you is we can see the rim of the egg in sulfur.
00:21:02Does that tell you whether it was a hard shell or a soft shell?
00:21:06We have been looking at this. We can see folding occurring and this unusual undulation.
00:21:13If it were a hard egg, we would expect splintered bits and broken bits, just like a chicken egg.
00:21:20This helps to tell us that it was soft.
00:21:22So, it was perhaps like a turtle?
00:21:24Absolutely.
00:21:25That's not the case, is it, with dinosaurs? Many dinosaurs had hard-shelled eggs.
00:21:30Yes.
00:21:31So, this is a new discovery about as darky pterosaurs.
00:21:34Absolutely. This is something that we are confirming for the first time.
00:21:40That flying pterosaurs had eggs like turtles.
00:21:44Yes. Much more reptilian-like than bird-like.
00:21:47And that can potentially tell us more about the environment in which these eggs were laid.
00:21:53How interesting. Yeah.
00:22:03Creatures that lay soft eggs tend to bury them in order to protect them.
00:22:08So, female pterosaurs probably look for places like Tannis to lay their eggs.
00:22:23Because the sandy soil here is just soft enough for the hatchling to dig itself out.
00:22:29Now, the pterosaur just has to make sure that the hole is perfect.
00:22:47Oh.
00:22:57Success.
00:23:00But it's not over yet.
00:23:02Pterosaurs had two ovaries.
00:23:04And they laid their eggs in pairs.
00:23:18Here, on the sandbank, sandwiched between the river and these glorious trees,
00:23:24Life at Tannis seemed to be thriving.
00:23:29Never a dull moment.
00:23:31But all that was about to change.
00:23:33The chain of events that led to the extinction of the dinosaurs began in the distant past,
00:23:47deep in space.
00:23:49Most scientists think it all started in a ring of dust, rocks, and debris known as the asteroid belt.
00:24:05It's usually an uneventful place.
00:24:07But it's thought that many, many millions of years ago, a rock was bumped into a new orbit.
00:24:22And diverted onto a collision course with planet Earth.
00:24:37Robert is building a vivid picture of late Cretaceous life at Tannis.
00:24:47And the team have found some more well-preserved footprints.
00:24:52So these are animals that were actually walking in the water?
00:24:55These guys would have been essentially on a mushy riverbank going down to drink at some point.
00:25:00You know, animals tend to congregate around the rivers.
00:25:04This print is 30 centimeters long.
00:25:08So I think this is from a type of dinosaur that we call a duck-billed dinosaur.
00:25:12And they would have been very common in the Cretaceous.
00:25:15They ate the plants in the area, and they got very large, 30 feet long.
00:25:22And there are more.
00:25:24This track, you see all the toes are very well-preserved.
00:25:27You even see a nail print at the tips of the toes.
00:25:30So the little toenails dug into the mud. I love this one.
00:25:37This is Robert's prize footprint.
00:25:42It has three toes.
00:25:45And it's longer than it is wide.
00:25:48So it's very likely to be a carnivorous dinosaur.
00:25:52It's so well-preserved that you can see the mark left by its sharp claw there.
00:26:00Hell Creek is well known for one carnivore in particular, T-Rex.
00:26:05This footprint is too small for an adult T-Rex.
00:26:12But it's possible that it was made by a young one.
00:26:15Robert also found this at Tannis.
00:26:29The crown of a tooth.
00:26:32Its shape and its serrated edge are indications that it comes from an adult T-Rex.
00:26:45Bite marks found on T-Rex bones show that they ate other T-Rexes.
00:27:11And a youngster would make an easy catch.
00:27:21But not this time.
00:27:32Very few footprints are preserved as fossils in Hell Creek.
00:27:36So if you find several in one place, as Robert has done,
00:27:41it's a reasonable assumption that there would have been many more nearby.
00:27:49And that supports the idea.
00:27:53The dinosaurs and pterosaurs were thriving at Tannis shortly before the impact.
00:27:58And if they were thriving,
00:28:11they must have been reproducing.
00:28:13Fossils from dinosaurs similar to T-Rex show they may have laid around 20 eggs in a circular nest.
00:28:34It's possible that, like crocodiles, they partly covered their eggs to keep them warm.
00:28:40For one T-Rex, a misfortune.
00:28:56For one T-Rex, a misfortune.
00:28:58But for all dinosaurs, a disaster was looming.
00:29:12Deep in space, the asteroid was approaching.
00:29:35Its journey would take it through the orbit of our neighboring planet, Mars.
00:29:39It's possible that, of course.
00:29:46Had the two collided, a catastrophe on Earth would have been avoided.
00:29:59But it was not to be.
00:30:00And Earth's fate was sealed.
00:30:05As Robert's dig continues, his vision of what happened at Tannis is finally starting to come together.
00:30:25It seems the sandbank was full of life.
00:30:31T-Rex, Triceratops, little mammals, alongside the footprints of other dinosaurs and pterosaurs,
00:30:39all in a very small area.
00:30:43See the scales?
00:30:44I do.
00:30:45Oh my god.
00:30:46That excites me just looking at it.
00:30:51Then Robert finds something truly remarkable.
00:30:58See the cracks already forming?
00:31:00Look at that.
00:31:01So we're going to have to really monitor that before we glue it.
00:31:03Because this is getting vulnerable now.
00:31:06An almost complete creature.
00:31:08To get this block out, we're freezing it.
00:31:20Robert is about to attempt something tricky.
00:31:25Steady?
00:31:27Let's go.
00:31:29To get the fossil out in one piece, they're trying to freeze it,
00:31:33using liquid nitrogen at almost 200 degrees below zero.
00:31:44Watch the footing.
00:31:46Lauren, I'm worried about brittleness here.
00:31:49Get that hammer.
00:31:50Give this a couple of whacks with the hammer.
00:31:53Okay.
00:31:55Move over five centimeters.
00:31:56Good.
00:31:59It's cracked loose.
00:32:00Yep.
00:32:02Okay, it's loose.
00:32:03So we have to get this out in one piece.
00:32:06One, two, three.
00:32:11Yee-haw!
00:32:13Total success.
00:32:14Total success.
00:32:17This is a technique used in archaeology for digging up human remains.
00:32:22We've got enough time to work with the fossil and not damage it.
00:32:26And I couldn't be happier.
00:32:31And the creature Robert found?
00:32:35A turtle.
00:32:39This is the fossil.
00:32:41Now it's been cleaned up.
00:32:42It's lying on its side.
00:32:45Here's the outline of its shell.
00:32:48The shape of the shell and the scott edges here tell us that this was a binid turtle.
00:32:59Robert's binid turtle looks very similar to modern cooter turtles and lived in the same sort of fresh water environment.
00:33:07For a turtle, tennis would have been ideal.
00:33:22Warm, shallow water.
00:33:27Plenty to eat.
00:33:28And lots of safe places in which to warm up in the late Cretaceous sunshine.
00:33:37The turtle fossil Robert found is almost complete.
00:33:46This is the underside.
00:33:49And this brown material up here is fossilized wood.
00:33:54It's the end of a stick that passes right through its body and comes out just here.
00:34:01So the evidence points towards this turtle having been impaled.
00:34:08A violent end to one of the many creatures found in the crumbly rock lair at Tannis.
00:34:13When I look at the animals and plants preserved in the sediments of Tannis and the footprints beneath it,
00:34:21I see a picture of a vibrant ecosystem, many different dinosaurs and a thriving, thriving place.
00:34:31After 10 years of digging, there is now enough evidence to piece together much of the story of Tannis and the creatures which lived here.
00:34:44Robert has found so many fossils, it looks as if, even at the very end of the late Cretaceous, Tannis was bursting with life.
00:34:55Full of the giant reptiles that had dominated the planet for more than 150 million years.
00:35:08It's impossible to know how much longer their reign would have continued.
00:35:13It's impossible to know how much longer their reign would have continued.
00:35:16Because all this was about to end.
00:35:19It's impossible to know how much longer their reign would have continued.
00:35:41The asteroid hit...
00:35:42...in what is now the Yocatan Peninsula in Mexico.
00:35:54It's called the Chicxulub asteroid after the town nearest to the center of its crater.
00:35:59Any living thing within 900 miles of the impact...
00:36:24...was destroyed by the blast.
00:36:26But what effect did the impact have on Tannis, nearly 2,000 miles away?
00:36:47To find out, Robert is looking for clues...
00:36:51...that might link Tannis to the actual day the asteroid hit.
00:37:01We've got some wood and pressed up against this.
00:37:04And all intertangled, we've got the carcasses of fish.
00:37:08Okay.
00:37:11That's a beautifully preserved tail.
00:37:12So that fish is going to be absolutely gorgeous.
00:37:14So part of the detail work that we're doing right now is going in and checking out all the individual elements in this mass death layer.
00:37:24Some of the evidence he's found so far has been hidden inside the fish themselves.
00:37:29In more ways than one, it literally is an operation of a Cretaceous fish.
00:37:36So we're performing surgery on this thing.
00:37:39Robert needs to open this fish's skull.
00:37:42And very carefully, we want to separate this from the rest of the fish.
00:37:50Okay.
00:37:55There we go.
00:37:57Opening up the fish.
00:37:59Got a nice ant that made a home in there.
00:38:03And beautiful, look at that.
00:38:05Okay, here we have the gill bars of the fish.
00:38:07Those are the bars that hold the filaments of the gills.
00:38:12Between the gill bars, all of these clusters of round objects, those are the ejectospherules.
00:38:18Ejectospherules are tiny balls that were once molten rock.
00:38:22They could be evidence of what Robert suspects, that creatures here died on the day of the asteroid strike.
00:38:31Those ejectospherules last saw the light of day when they were flying through the air 66 billion years ago.
00:38:37After a large asteroid impact, a mix of vaporized and molten rock is propelled into space.
00:38:58There it cools, solidifying into tiny glass droplets.
00:39:03Some carry on deeper into space.
00:39:10But most are pulled back to Earth by gravity.
00:39:13After a major asteroid hit, trillions of ejectospherules would fall from the sky.
00:39:29Then, over millions of years, pressure and chemical reactions in the ground would turn most of them to clay.
00:39:36They'd look something like this.
00:39:41So, finding spherules in the gills of a fish, as Robert has done at Tannis, suggests the fish sucked them in while the spherules were still falling.
00:39:51So, these creatures could have died at the time of an asteroid impact.
00:40:02Once Robert begins to look for ejectospherules, he finds more and more and realises the thick, crumbly layer of rock at Tannis is full of them.
00:40:13I mean, this stuff is, oh my god, look at that one.
00:40:19These things are just gorgeous.
00:40:22Ejectospherules like this give us a fingerprint of where they came from.
00:40:26If these spherules were connected to the Chicxulub impact, then the whole crumbly layer could be full of evidence of what happened on the day the asteroid hit.
00:40:38That's a good one.
00:40:40Oh, is that a droplet right there?
00:40:42To see if that's the case, Robert needs to find a spherule that hasn't turned to clay.
00:40:49Oh my god, that's a beautiful droplet.
00:40:52Okay.
00:40:52The small pieces of orange material that Robert and Lauren are digging up may be able to help.
00:41:01They're amber.
00:41:04If there was anything flying through the air at that time, this is where it's going to get caught.
00:41:10The amber they're collecting was once sticky resin oozing out of a late Cretaceous tree trunk.
00:41:16It's a way for the tree to protect itself like a scab forming on a cut.
00:41:32Anything covered by the resin would be frozen in an amber thyme capsule.
00:41:36If they find a spherule preserved in amber, it could be analyzed.
00:41:48To see if it comes from the Chicxulub asteroid impact.
00:41:51So during this batch, we were incredibly lucky that we came across two completely unaltered spherules.
00:42:03This spherule could be something amazing.
00:42:07Evidence preserved well enough to analyze for chemical clues.
00:42:11If so, it could link Tannis directly with the Chicxulub impact and the last day of the dinosaurs.
00:42:22To investigate, Robert is joined at the Diamond Light Source by Professor of Natural History Phil Manning of the University of Manchester.
00:42:40They've already run initial tests on the spherules in America.
00:42:45What have you found out so far?
00:42:47These little glass spherules, these globs of molten material from the impact site,
00:42:52have a chemical signal that ties it with where they came from.
00:42:55Because when an asteroid hits, it melts the ground that it hits,
00:42:59but also that glass has a little bit of contamination from the asteroid itself.
00:43:04And that gives you a unique geochemical fingerprint.
00:43:07We can see once we've scanned it and looking at spherules from other sites in North Dakota,
00:43:12we can get a baseline for what the ejector should look like when it's related to the Chicxulub crater.
00:43:19You can see each element here and the ratios of those elements.
00:43:23And when we look at Tannis, it's a match.
00:43:26I mean, it perfectly overlays.
00:43:29So I think this is powerful evidence supporting that Tannis and Chicxulub are linked.
00:43:35And what do these findings mean for the rest of the fossils that you're finding in Tannis?
00:43:41This data is key for the entire site.
00:43:44Because once you have that link and you know what impact affected Tannis,
00:43:49then you essentially know that every object in that site,
00:43:52all the animals and the plants and everything buried in those sediments,
00:43:57are linked to the last day of the Cretaceous.
00:44:01And the synchrotron here in the UK reveals something even more remarkable.
00:44:07So this is showing a beautiful synchrotron scan of the half of one spherule.
00:44:16The glass is a good geochemical fingerprint, and we've got calcium, some iron, we've got
00:44:23strontium. But when we look at the entire thing, we see something quite unexpected.
00:44:28That's your entire spherule.
00:44:32What's this?
00:44:33In this, we've got a little bit of a nugget.
00:44:36There is a little particle right there.
00:44:38So we scan it, and that's a lot of iron in there.
00:44:42Over here, we've got chromium, a big peak in chromium.
00:44:46Over here, we've got a big peak in nickel.
00:44:48And the abundances of iron, nickel, and chromium all together,
00:44:52that matches what you expect to see in a meteoric body.
00:44:55That does not match what you would normally have down here.
00:44:58So this is extraterrestrial material.
00:45:02If you were to sort of grind up and stuff into a spherule, a piece of meteorite,
00:45:09that's what it's going to look like.
00:45:11This could be a piece of the Chichalube asteroid.
00:45:14The piece of the bullet that killed the dinosaurs.
00:45:16Robert could have found a fragment of the asteroid itself in Tannis.
00:45:30Physical evidence linking this site to the Chichalube impact.
00:45:35But Tannis is almost 2,000 miles away from where the asteroid hit.
00:45:40So exactly how did it cause the creature's deaths?
00:45:48To answer that question, Robert is searching in the mass death layer.
00:45:56Right here, we've got this intertangled mass of fish.
00:46:00There's one fish here.
00:46:01Another sturgeon goes this way underneath the body of a paddlefish.
00:46:04There's another sturgeon that goes this way underneath this log and continues out the other side.
00:46:10And his head hit that log and is deflected downward at a 90 degree angle.
00:46:17Robert uncovered a tangled mass of fossilized creatures and logs surrounded by spherules
00:46:25and crushed together in what's known as a log jam.
00:46:29He has a theory that the creatures were swept to their death in some kind of turbulent surge of water
00:46:35and quickly entombed in sediment, which is why they're so well preserved.
00:46:41But what could have caused the wave?
00:46:47One theory is a tsunami.
00:46:50The asteroid hit at sea.
00:46:57Recent studies show it may have caused the wave almost a mile high.
00:47:02The height of the wave would have gradually reduced as it spread across the oceans.
00:47:22In the late Cretaceous, North America was divided by a narrow sea that's been called the Western Interior
00:47:29seaway. The tsunami could have traveled up this towards Tannis.
00:47:37But there's a big question about the tsunami idea.
00:47:42The timing.
00:47:45Oh, which fish is that?
00:47:46It's a new contact.
00:47:50If a tsunami killed the fish, it would have to have hit while ejector spherules were falling.
00:47:56Because spherules were found in the fish's gills.
00:48:03So how long after impact did the spherules arrive at Tannis?
00:48:09Pretend this ball of foil is a piece of ejector coming out of the crater.
00:48:13It would then go on an arc path, ballistic trajectory, out of the crater and to wherever it lands, in this case Tannis.
00:48:19If we know the distance between myself and the landing site, and if we know the size of that ball,
00:48:27we can accurately calculate how long it would take to get there.
00:48:30The result is surprising. Robert and his team calculated that these ejector spherules
00:48:41landed at Tannis between 13 minutes and two hours after the impact.
00:48:46If a wave killed the fish, it must also have reached Tannis within two hours.
00:48:58Data from recent tsunamis show even a powerful one would take much longer than that,
00:49:04to travel almost 2,000 miles from the impact site to Tannis.
00:49:08So if it wasn't a tsunami, what could have caused the surge of water at Tannis?
00:49:25Professor Stein Bondovic is an expert in tsunamis.
00:49:29The fjords in Norway are very special. We have tall mountains surrounding bodies of water,
00:49:43so the water is usually very pumped. In 2011, something very strange happened.
00:49:51The water in the fjord began to move violently. The height of the water
00:49:56of the water increased by one and a half meter. Like a maelstrom with the turbulent water,
00:50:04someone said that the fjord was boiling. News started to roll in. There'd been an earthquake
00:50:115,000 miles away in Japan. A journalist from the local newspaper called me and he said that
00:50:20people were observing waves here in the fjords. I got a video clip of the waves. I saw immediately that
00:50:30they looked like a tsunami wave. So later in the afternoon, you can see that the fjord is perfectly calm.
00:50:39But at the beach here, you could see that the water is sloshing back and forth.
00:50:42And no one had ever seen anything like it. Some people got very upset and afraid.
00:50:54A magnitude 9 earthquake had devastated the northeast of Japan around Fukushima.
00:51:00But how did that affect a fjord so far away?
00:51:10So no one in Norway could feel the earthquake.
00:51:15But I could see that the times matched the arrival of the waves here in the fjord.
00:51:19Eventually, Stein and his team realized that this might have something to do with
00:51:30seismic waves, shock waves that pass quickly through the earth during an earthquake.
00:51:38So it took only 12 minutes before the first signal of the earthquake in Japan reached
00:51:43all the way here to western Norway.
00:51:45So it was the seismic waves that caused the normally calm water in the fjord
00:51:53to slosh turbulently back and forth.
00:51:57Just thinking of that, scientifically, it's fantastic.
00:52:08Could something similar have happened in Tanis?
00:52:15It's fantastic.
00:52:17Trying to find out is geophysicist Professor Mark Richards,
00:52:22who's been studying the site at Tanis for several years.
00:52:27He's working with Robert to discover what could have caused a surge of water here.
00:52:32A tsunami can't get here in less than minimum 12 hours.
00:52:44But seismic waves traveling from the Yucatan impact site to North Dakota can arrive here fairly quickly.
00:52:50In the late Cretaceous, the western interior seaway that divided North America could have been connected to Tanis through a system of rivers.
00:53:03If you have a very large body of water, like the western interior seaway,
00:53:14and you can shake it back and forth, you can generate a large water wave coming up this river at Tanis.
00:53:21So seismic waves from the impact could have caused surges of water in the Tanis river system.
00:53:34Seismic waves get here quickly enough, coming up the Tanis river,
00:53:39inundating this area arriving at the same time these spirals are still falling out of the air.
00:53:47The mystery of the wave and the thick layer of crumbly rock has been solved.
00:53:53Seismic waves traveling through the earth could have caused powerful surges of water at Tanis.
00:54:02Possibly carrying mud and marine creatures like ammonites from the western interior seaway.
00:54:09Dumping them on the Tanis sandbank and burying everything at the same time as spherials fell.
00:54:27Over millions of years, the mud would turn into the layer of crumbly rock.
00:54:33And that's the beauty of Tanis. What you're seeing is a deposit
00:54:40that is literally recording the last, say, 45 minutes to an hour and a half of the Cretaceous.
00:54:48If the extinction of the dinosaurs was a crime, the detectives solving it would have plenty of evidence.
00:55:05They would see that the asteroid was in the right place at the right time.
00:55:10They would see that no dinosaurs survived after the hit.
00:55:15They would have a piece of the murder weapon, a fragment of the asteroid.
00:55:19But they would be missing one very important thing. A body.
00:55:30No one has ever found the fossil of a dinosaur that was killed by the effects of the asteroid impact.
00:55:37But Robert did find part of a triceratops in the crumbly lair at Tanis.
00:55:44So could that be the remains of a dinosaur that died on that day?
00:55:49I'm still dubious about the horn. I kind of want to keep the horn in the jacket.
00:55:52I think if you took it off, at least take this section off to see what's going on under here.
00:55:57Yeah.
00:55:59To find out, the team needs to establish cause of death.
00:56:03Which can be difficult when you only have a piece of skin and a horn to go on.
00:56:11This is the horn after they'd cleaned it up.
00:56:15The team is particularly interested in these lines here.
00:56:19And they found that the fractures go right through the horn.
00:56:24So rather than dying as a result of the impact,
00:56:28they wondered whether it had been killed in a fight.
00:56:37But when they looked at the fractures in more detail,
00:56:39they found signs of new bone growth here.
00:56:42So it looked as though the triceratops survived the event that broke its horn.
00:56:56Could this triceratops have survived until the day of the impact?
00:57:01The team found evidence, including sagging in the skin,
00:57:05which suggested that there was decay underneath.
00:57:09That means its body had started to rot before it was entombed and preserved by the surge.
00:57:16So it seems that this dinosaur didn't die as a result of the asteroid impact.
00:57:22Perhaps in the months before the impact,
00:57:27the broken horn put the triceratops at a disadvantage over its rivals.
00:57:35And that might have led to starvation.
00:57:49And that might have led to starvation.
00:58:02Robert has still not found direct evidence of a dinosaur that was killed by the asteroid.
00:58:20We've got all these bones in the ground right now,
00:58:22but the one thing that we would just dream of finding is that one dinosaur that died on the day of the impact.
00:58:33And the weather isn't helping his search.
00:58:36That theropod print is toasted.
00:58:57Yeah, it was in a low corner.
00:58:58It's full of mud and water.
00:59:02The problem is it's wet.
00:59:03Look, see, if we're not careful, we're going to lose the print.
00:59:08And that's the biggest theropod print we've got.
00:59:11I see some areas that could use glue right now too.
00:59:16The team is racing to excavate the footprints,
00:59:19along with dozens of fish fossils tangled together in a logjam before storms wash them away.
00:59:26We're up against the clock here.
00:59:29The stuff that could be exposed right now is going to get ruined by the rain.
00:59:36But then Robert comes across something that looks very unusual.
00:59:40What is going on right there?
00:59:45Are we sure this isn't crocodilian?
00:59:47That's not crocodilian.
00:59:48No.
00:59:49All right, I'm going to try this piece right here.
00:59:52I'll go in from the top and then twist up and it separates on right on that line.
00:59:56Oh, that's skin right there.
00:59:58That's actually scaly skin.
01:00:01No, no, no, no, no.
01:00:02Look, look, look, look at that pattern right there.
01:00:04Have you ever seen elongated scales like that before, Dave?
01:00:08Scutalates and birds.
01:00:10Just careful.
01:00:12Oh, it's changing again.
01:00:14It's changing again.
01:00:17We've seen it for the first time in 66 million years.
01:00:21I think we've got ourselves a dinosaur.
01:00:27A dinosaur fossil.
01:00:29And unlike the triceratops, this is located in the logjam,
01:00:34the mass death layer surrounded by the fish with spherules in their gills.
01:00:44This is the most incredible thing that we could possibly imagine here,
01:00:46the best case scenario.
01:00:48We're excavating this mass death layer of fish from the surge sent up by the impact,
01:00:53and we've got dinosaur remains.
01:00:56The one thing that we would always want to find at this site,
01:01:00and here we've got it.
01:01:01This is unreal.
01:01:03I cannot process this in my brain.
01:01:05No, I am absolutely blown away by this.
01:01:08Just my heart is literally pumping out of my chest wondering what is behind there,
01:01:11just a couple of centimeters back in the outcrop.
01:01:14What is waiting for us back there?
01:01:15The team keeps digging.
01:01:24So this could be a rib cage.
01:01:25It could be laying against ribs that are curved.
01:01:27There's something here.
01:01:30That's hard.
01:01:30More bone.
01:01:31That's bone right next to the skin.
01:01:33That's an articular surface right there.
01:01:35So this is either a hip or a shoulder element.
01:01:37After hours of painstaking work.
01:01:47And we can go from the thigh of the animal.
01:01:50There's the knee.
01:01:51And then you've got the little calf muscles of the dinosaur that are bulging out.
01:01:56And you go down to the ankle bones.
01:01:59And these are the toes of the feet.
01:02:02We've got nails at the tips of the toes.
01:02:04It's a beautifully preserved leg.
01:02:05All articulated.
01:02:06Covered with skin.
01:02:09The complete leg of a dinosaur.
01:02:13In my wildest dreams, I never expected to find a dinosaur leg in this deposit.
01:02:17Yeah.
01:02:17I mean, and then it's got skin and tissue.
01:02:21It does look just like a drumstick.
01:02:23It looks like a Thanksgiving turkey just laid out in the ground.
01:02:27And this weird scale pattern on the thigh of the animal, which we've never seen in a dinosaur before.
01:02:32Well, Thessalosaurs don't have any form of defense.
01:02:36So they have to have camouflage or something.
01:02:38That's a good point.
01:02:39So this could have been some sort of camouflage marking.
01:02:41Yeah.
01:02:43Rumpet thinks he has found the body in question.
01:02:47A dinosaur that might itself have witnessed the cataclysmic impact.
01:02:56Dinosaur fossils are not known from the last years of the Cretaceous.
01:03:01And it was unclear whether they were already extinct or in decline or what was going on.
01:03:06So they were just sort of absent.
01:03:11And this answers that question.
01:03:12Were dinosaurs still there then?
01:03:14Well, yes, this one likely died in that search.
01:03:23For such big claims, Robert needs verification.
01:03:30He's brought the dinosaur leg to London to get a second opinion.
01:03:34And then here are the pads of the toes.
01:03:37We see all those beautiful scales lined up.
01:03:39From Professor Paul Barrett, an expert in Ornithischian dinosaurs from the Natural History Museum.
01:03:49So what do you think this might be?
01:03:51When we look at the leg, it has claws.
01:03:54Like the claws we see in small, agile, bipedal, running dinosaurs that are plant eaters.
01:04:01We can rule out things like Triceratops, partly just because it's not big and stocky.
01:04:06And the proportions of those legs are also different from some of the other plant eaters we see,
01:04:10in that they have this rather long ankle and shin compared with its thigh bone.
01:04:16So as we narrow those possibilities down,
01:04:18what we're left with probably is an animal called a Thessalosaur.
01:04:30Thessalosaurs lived next to rivers where there was plenty of rich vegetation to feed on.
01:04:35They had leaf-shaped teeth common amongst herbivores and claws on their short front limbs.
01:04:46Excellent for digging.
01:04:56But how did Robert's Thessalosaur die?
01:05:09Could it have been killed by another dinosaur?
01:05:12It's a possibility.
01:05:14This is a relatively agile animal.
01:05:17And that turn of speed would have been its primary defence against the large predators
01:05:21living alongside it.
01:05:26So to escape a hungry T-Rex, a Thessalosaur's first line of defence
01:05:36would have been to run.
01:05:40But it may have had another defensive trick.
01:05:43It's possible Thessalosaur were able to swim.
01:05:57It doesn't seem to me like there is any evidence that this animal was predated.
01:06:15None of the obvious tooth marks or leftover bits of carnivore teeth to suggest it's been eaten.
01:06:21So how do you think it died?
01:06:23It didn't have any particularly nasty diseases when it died.
01:06:27As we can see that the bones look okay.
01:06:29So this is an animal that was probably living and healthy at the time that this happened to it.
01:06:34Could this be a victim of the meteor strike?
01:06:40I think it's entirely possible.
01:06:42This is actually a shoulder bone.
01:06:44And this bone in the living animal would actually be way over here.
01:06:47And similarly this little bone here would have been from about maybe a third of the way
01:06:52along the tail, maybe halfway down.
01:06:55So somehow these two bones have been telescoped together.
01:06:59Yeah.
01:06:59So maybe this animal's been tumbled around.
01:07:02We've ruled out a lot of other possible causes of death for this animal.
01:07:06So it could well be that this is an animal that was there being tumbled around in its death
01:07:11throes in that river as a result of the asteroid impact.
01:07:15Well, it is exactly analogous to those human bodies found in Bombay.
01:07:21It's very similar in terms of that quick entombment.
01:07:24Yes.
01:07:25And it's almost as evocative.
01:07:27That's absolutely true.
01:07:29You've got literally the blink of an eye at the end of the Cretaceous,
01:07:33snapped up into history.
01:07:34And there it is ready to be dug up.
01:07:36Wow.
01:07:50After years of investigation, Robert has found out a great deal about the creatures which lived at
01:07:56Tannis. And he knows that many of them were alive on that fateful day when the asteroid devastated
01:08:04our planet. But how exactly did they die? Robert's finds now allow us to tell the story of that day
01:08:13and finally answer that question.
01:08:19One of the most important days in Earth's history probably started much like any other late spring
01:08:25morning.
01:08:31We know the season because Robert found fossils of young fish that died at the size they reach at
01:08:37that time of year. This agrees with evidence already found by other scientists.
01:08:46Perhaps this day that would end with so much death began with something different.
01:08:51A new life.
01:09:05No one can be certain of the exact timings of the day when the asteroid collided with our planet.
01:09:25But it's estimated that within just 40 minutes of the impact, the consequences for the creatures
01:09:32of Tannis would have been profound.
01:09:38Based on Robert's finds and the latest evidence from other scientists, this is how the catastrophe
01:09:44might have unfolded. The asteroid is around seven miles across, bigger than Mount Everest,
01:09:55and traveling at close to 45,000 miles an hour.
01:10:00The impact causes an explosion bigger than a billion Hiroshima atomic bombs.
01:10:17At Tannis, almost 2,000 miles away, it's completely silent.
01:10:24But at the impact site, the asteroid vaporizes.
01:10:36More than three trillion tons of rock are ejected into space in a blast of superheated violence.
01:10:43A colossal earthquake followed by a ring of massive tsunamis.
01:10:57Tannis, almost 2,000 miles away, it's completely silent.
01:11:07All the while, the creatures at Tannis go about their business.
01:11:16Just like any other day.
01:11:27The evidence suggests that baby pterosaurs emerged from the egg, ready to fend for themselves.
01:11:45And that includes...
01:11:49Flying?
01:11:52Well, almost.
01:11:57Flying?
01:12:02Elsewhere, as the devastation spreads out across North America towards Tannis...
01:12:09Dinosaurs and creatures of all shapes and sizes are obliterated by the blast.
01:12:27At Tannis, for a few more precious minutes, life carries on as usual.
01:12:34But the clock is ticking.
01:12:35The blast from the impact never reaches Tannis, but seismic shockwaves do.
01:12:49The blast from the impact never reaches Tannis, but seismic shockwaves do.
01:12:55They are far more powerful than any earthquake ever recorded.
01:13:13The Thessalosaur might head for a place of safety.
01:13:30But seismic waves are now slowly shaking the whole region, causing water to slosh and churn.
01:13:36The Tannis' strange currents in the river give a hint of what is still to come.
01:13:47The Tannis' strange currents in the river give a hint of what is still going on in the river.
01:13:57Next, it begins to rain.
01:14:02Ejector spherules are falling back to Earth.
01:14:05As the spherules begin their fall, friction heats them until they're red-hot.
01:14:27Then the heat transfers to the air.
01:14:32Temperatures rise with every second.
01:14:35As the heat builds, the creatures of Tannis are fighting for their lives.
01:14:52And then, as seismic waves continue to slowly rock the whole region...
01:14:57A violent surge wave, ten metres high, rushes up the Tannis river.
01:15:07Surviving the turbulence of the surge is a challenge, even for the best swimmers.
01:15:20And then, as seismic waves...
01:15:21And then, as seismic waves...
01:15:22And then, as seismic waves...
01:15:23And then, as seismic waves...
01:15:25Surviving the turbulence of the surge is a challenge, even for the best swimmers.
01:15:31And then, as seismic waves...
01:15:31And then, as seismic waves...
01:15:33Then, the powerful rocking of the river system slowly begins to draw the water back the way it came to the river.
01:15:38And then, the powerful rocking of the river system slowly begins to draw the water back the way it came.
01:15:50Swimming may have saved the Thessalosaur in the past, but not this time.
01:16:06A large, robust animal like a T-Rex might have survived the surge.
01:16:23As might a hard-shelled reptile.
01:16:27But there is much more to come.
01:16:30As billions of tons of super-heated spherules continue to fall...
01:16:35The atmosphere gets even hotter.
01:16:39Igniting dead leaves and sparking wildfires.
01:16:50Earthquakes.
01:16:53Fire.
01:16:55Devastation.
01:16:59Little would survive for long.
01:17:01Or...
01:17:02On land.
01:17:09Or in the air.
01:17:10As the air reaches the temperature of an industrial oven...
01:17:21As the air reaches the temperature of an industrial oven...
01:17:34Those that live deep underground...
01:17:39may have a better chance.
01:17:49As the slow sloshing of the river system continues...
01:17:55Another powerful surge hits.
01:17:57There is no escaping the destruction.
01:18:19For many of the creatures of Tannis, their stories end underwater.
01:18:32In less than two hours, the world has changed forever.
01:18:49The mud the surge waves leave behind will gradually turn into the thick layer of crumbly rock,
01:19:03entombing the creatures which died here.
01:19:05Until 66 million years later, when they are finally unearthed.
01:19:21Robert's finds have helped us understand in remarkable detail what happened at Tannis in the minutes after the asteroid impact.
01:19:33But what about the rest of the world?
01:19:38The impact triggered catastrophic events such as earthquakes all over the planet.
01:19:43And as ferules continued to fall, wildfires may have sprung up around the globe.
01:19:54As that horrific day drew to a close, many of the world's dinosaurs were already dead.
01:20:10Research shows that the angle at which the asteroid hit and the sulfur-rich rocks at the impact site amplified the devastation.
01:20:20Billions of tons of sulfur were ejected into the atmosphere, blocking the sunlight.
01:20:28Without light, most plants died and food became scarce.
01:20:35As the weeks and months passed, any dinosaur left alive would have died of hunger.
01:20:43In the oceans, it was the same.
01:20:46Nearly all of the world's plankton disappeared, leading to the starvation of most marine creatures.
01:20:55It's thought that the nuclear winter that followed caused a global temperature drop of at least 25 degrees centigrade.
01:21:04The fossil record tells us that this huge change in climate
01:21:08marked the disappearance of three-quarters of all species, including the dinosaurs.
01:21:16The planet was in semi-darkness for around a decade as dust and soot slowly fell to Earth.
01:21:26But then came something wonderful.
01:21:30A new beginning.
01:21:36Once the dust cleared from the atmosphere and the sunlight returned,
01:21:40plant life was gradually restored, led by ferns, the spores of which had lain dormant deep underground.
01:21:53And the world began to turn green once more.
01:21:56But what about the animals?
01:22:03Back at Tannis, Robert has unearthed something that could have helped save some of the creatures from the devastating fires.
01:22:11We saw a little thing poking out, so we kind of followed it back.
01:22:15And I'm so glad that we did, because what we have here is a fossil burrow from an animal 66 million years ago.
01:22:24The only animals that would have been around back then that would likely build a burrow like this
01:22:29would be the small mammals, roughly ferret-sized, and also some reptiles.
01:22:35If it is from a mammal, this is sort of a window into the lifestyle of some of our oldest ancestors out here.
01:22:41This guy would have burrowed sideways right into the riverbank.
01:22:47They actually have some scratch marks on there from the interior when they were digging it,
01:22:52going back, and he would have lived back here and sought shelter from the dinosaurs,
01:22:56because they just did not want to get eaten.
01:23:05Burrows are part of the reason that mammals survived the great extinction.
01:23:11During the nuclear winter, a burrow would have provided warmth, protection, and a place to store food.
01:23:26Mammals that survived were resourceful omnivores,
01:23:30and insects would have been a plentiful source of food.
01:23:33And they had another advantage.
01:23:42Their size.
01:23:45If conditions are right, many animal species get larger as they evolve over millions of years.
01:23:52Take T. rex as an example.
01:23:55This is a cast of the lower jaw of a predecessor called Gorgosaurus, which lived 72 million years ago.
01:24:05Whereas this is the cast of the lower jaw of a T. rex, which lived five million years later.
01:24:14Look at the difference in size.
01:24:16But the bigger the creature, the more energy they need to stay alive.
01:24:21So when catastrophe strikes and food is scarce,
01:24:24the largest tend to die out, whilst the smallest often survive.
01:24:33That's one of the reasons why many of the smaller mammals lived through the great darkness.
01:24:39And they weren't alone.
01:24:44Robert's fossil turtle may have been unlucky, but many others survived.
01:24:53As did crocodiles, snakes, and many fish species.
01:24:59And as for the dinosaurs, did the impact really kill them all?
01:25:06Well, this beautiful fossilized feather isn't from a bird, but from a predatory dinosaur.
01:25:14So we have to be careful when we say that dinosaurs are extinct.
01:25:18Because what we call birds originally evolved from the smallest feathered dinosaurs.
01:25:26So to be correct, we should say all non-avian dinosaurs are extinct.
01:25:35Robert's finds have given us a better idea than ever before
01:25:41about what happened on the day that led to the extinction
01:25:47of the largest beasts ever to walk the earth.
01:25:50dinosaurs were perhaps some of nature's most extraordinary creatures,
01:25:59dominating the planet for over 150 million years before they became extinct.
01:26:08But extinction comes in different forms.
01:26:11And many of the amazing creatures and plants alive today are also threatened.
01:26:17It's possible that humanity is having as big an impact on the world as the asteroid
01:26:23that ended the age of the dinosaurs.
01:26:27As human beings, we are unique in our ability to learn from the distant past.
01:26:33Now, we must use that ability wisely and do our very best to protect the millions of species
01:26:41for whom, alongside us, this planet is home.
01:26:53Animals fighting for their families against the odds.
01:27:08Watch the list is two with David Attebra.
01:27:10That's on BBC iPlayer now.
01:27:12Former MasterChef champions are back, but this time they're hungry.
01:27:16New MasterChef.
01:27:17That follows next here on BBC One.
01:27:19And, hold on tight, searching for the best tractor drivers.
01:27:22It's the Fast and the Farmer-ish on BBC Three.
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