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00:00:0066 million years ago, planet Earth was very different from today.
00:00:20Back then, one of our closest ancestors might have looked something like this little furry
00:00:26creature.
00:00:33The rulers of the land were giant reptiles.
00:00:50Dinosaurs, 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.
00:01:20But what happened to them all?
00:01:24Sixty-six million years ago, an asteroid hit the Earth.
00:01:28And scientists think that it was this collision that wiped out the dinosaurs.
00:01:33But no one has ever found direct evidence of that.
00:01:38In fact, no one has ever found the fossil of a dinosaur that died within a thousand
00:01:43years of the impact.
00:01:46However, a remarkable dig site promises to change that.
00:01:56It's in the Hell Creek Formation in the American Midwest.
00:02:03These badlands are rich in prehistoric remains, from triceratops to pterosaurs.
00:02:18And here, one patch of land about the size of a football pitch is yielding a collection
00:02:24of astonishing fossils.
00:02:29The precise location is a closely guarded secret, because this place may hold evidence
00:02:38of one of the most dramatic events in all the four and a half billion year history of
00:02:43our planet.
00:02:51For ten years, a paleontologist and his team have been trying to find out exactly what
00:02:56happened here.
00:02:58You're at the edge of your seat every moment trying to dig this stuff up.
00:03:01It's like trying to defuse a nuclear weapon while you're in a rainstorm.
00:03:06He's named the site Tannis, and believes it could be a mass graveyard of creatures that
00:03:11were killed in the catastrophic asteroid strike, a site that could reveal not only how the
00:03:22last dinosaurs lived, but how they died.
00:03:28If the dig team is right, Tannis could be a place where the remains of a long lost world
00:03:35are frozen in time.
00:03:39A place that gives us, for the first time, an unprecedented window into the lives of
00:03:48the very last dinosaurs, and a minute by minute picture of what happened on the day
00:03:59the asteroid hit.
00:04:18This landscape is full of fossils dating from the late Cretaceous, the period which
00:04:27began around 100 million years ago and ended 66 million years ago when the dinosaurs vanished.
00:04:37Paleontologist Robert de Palma wants to find out more.
00:04:42I think anybody who has ever liked dinosaurs in the past, or still does, has thought at
00:04:47one point or another, well, what happened to them?
00:04:50Why are they not here anymore?
00:04:52So many different theories are out there, and nobody has a tight answer to that question.
00:05:02Judging from fossil evidence, this is what Hell Creek looked like in the late Cretaceous.
00:05:09There were low-lying marshy flood plains, intercut by river channels, and covered with
00:05:19horsetails, ferns, and trees.
00:05:23Back then, it was warm and wet here all year round.
00:05:30Tannis lies in the northeastern 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, well, Robert is hoping to find out more about what
00:06:02that was like.
00:06:08A sandbank lying between a river and a forest would one day become what Robert now calls
00:06:15Tannis.
00:06:20He and his team have been digging here since 2012.
00:06:25So somewhere from between there and down here is where that came from, wouldn't it come
00:06:28from up above?
00:06:29Hey, look at this.
00:06:30What?
00:06:31Yeah, yeah, yeah.
00:06:32Okay.
00:06:33And what they found is unexpected.
00:06:36Here we've got this freshwater environment of the Hell Creek formation, and this shocking
00:06:43red-green color is coming from the shells of ammonites, a marine organism, kind of like
00:06:47a coiled snail in appearance.
00:06:49So we've got this marine organism that's been thrown up into this freshwater environment,
00:06:55and they do not belong here.
00:06:58What they got here is a mystery.
00:07:01And there's more.
00:07:02I'm just going to go ahead and plane down some of this rock.
00:07:07Sitting just above the ammonites is something that many dinosaur hunters are desperate to
00:07:13find.
00:07:14So this orange layer right here is composed 100% of impact-related debris that is enriched
00:07:21in iridium.
00:07:23Iridium is an element that's rare in the Earth's crust, but it's common in asteroids.
00:07:30The layer it's in is called the K-P-G boundary.
00:07:34Oh, dear.
00:07:36Really?
00:07:37Yeah.
00:07:38It's made up of dust and debris from a huge asteroid impact.
00:07:45Look at that.
00:07:48That's amazing.
00:07:49Yeah, yeah, yeah, yeah, yeah.
00:07:50That's what we want.
00:07:51Okay.
00:07:52So it's coming from this area here.
00:07:53That's where these pieces are coming from.
00:07:55The boundary separates the age of the dinosaurs from the age of mammals.
00:08:00So the rocks here come from about the time that the dinosaurs became extinct.
00:08:06No rattlesnakes.
00:08:08What makes the site even more exciting is the rock layer right beneath the boundary
00:08:12where Robert found the ammonites.
00:08:15The rock here is really not quite rocky as you would expect dinosaur bones and things
00:08:19to be encased.
00:08:20You expect really, really hard rocks and jackhammers and things like this, but it's very, very
00:08:24crumbly and it just falls apart in your hands.
00:08:30As well as being crumbly throughout, this layer of rock is also around a metre thick,
00:08:36which along with other unusual features, makes Robert think that something very strange must
00:08:42have happened here.
00:08:48Maybe a flood or a mudflow, 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 layer would have been quickly entombed,
00:09:03like the bodies in the volcanic ash of Pompeii.
00:09:11Robert knows from the geology that anything he finds at Tannis will be tantalisingly close
00:09:17to the end of the age of the dinosaurs, and could be so well preserved that it could reveal
00:09:23new evidence that would bring this time period to life in a way no one has ever done before.
00:09:35Robert digs at Tannis each summer, the only time the weather allows him to do so.
00:09:42Come on down and check out this lens over here.
00:09:46In order to understand how the impact affected life on Earth, you really need to get a very
00:09:51clear picture of what the world was like right before.
00:09:55That is a critical part of the story.
00:10:00Paleontologists Dr David Burnham and Lauren Gurchie have been digging with Robert for years.
00:10:10Oh, wow.
00:10:13See the brown?
00:10:14Yep.
00:10:15That must be a tubercle right there.
00:10:16Yep.
00:10:17And it seems today is their lucky day.
00:10:19Oh my god, look at that.
00:10:22Look the scales are preserved.
00:10:23It's like doing a freaking dissection.
00:10:26Oh my god.
00:10:28Geology 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.
00:10:37How big are they there?
00:10:38I got a, I got a one with a projection over here.
00:10:42What?
00:10:43Oh.
00:10:44Oh.
00:10:45It's right there.
00:10:46I've only seen that on one other specimen.
00:10:47Oh, on life.
00:10:48Yep.
00:10:49This is the closest thing to getting a touch of a living, breathing dinosaur.
00:10:52It is.
00:10:53They found something extraordinary.
00:10:57It is so exceedingly rare, a piece of triceratops skin in the Hell Creek formation.
00:11:03It may look like an impression in the rock, but this is skin that has been fossilized
00:11:12and over millions of years has turned to stone.
00:11:18Triceratops bones are relatively common finds in Hell Creek, but skin in such condition
00:11:24as this is very rare indeed.
00:11:28The size and the patterning of the scales together with the age and location of the
00:11:33rocks where it was found strongly suggests that this is from a triceratops.
00:11:41The brown colour contains traces of organic material, so it might even be possible from
00:11:47this to work out which pigments were in it.
00:11:52Finding and studying such well-preserved fossils as this helps paleontologists build a much
00:11:57more detailed picture of how these creatures lived.
00:12:03Combining this information with insights from scientists around the world makes it possible
00:12:09to speculate about what life in the late Cretaceous might have been like.
00:12:22We know from bones that adult triceratops could reach nine metres in length and three
00:12:28metres in height.
00:12:34Rocks on the fossil also show us that this one was badly scarred.
00:12:49Triceratops were plant eaters.
00:12:56Other fossils tell us that they had sharp beaks and hundreds of teeth that enabled them
00:13:01to shred tough plants such as these cycads.
00:13:14Almost 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.
00:13:30So they were probably territorial, chasing rivals away.
00:13:41And perhaps marking their territories.
00:13:49If you weigh more than an African elephant, there's not much that can bother you.
00:13:58Except perhaps a little mammal.
00:14:17Robert found these jaw bones in a fossilised burrow at Tannis.
00:14:23The shape of this tiny bone and tooth means it's most likely come from what's known
00:14:29as a pediomyid, an early mammal, and a type of marsupial.
00:14:39Robert also discovered fossilised nuts and seeds in the burrow.
00:14:45So we have an idea about what it might have eaten.
00:14:56Robert's finds are adding to our knowledge of the complex world at the very end of the
00:15:02late Cretaceous.
00:15:04And it's not just the fossilised creatures.
00:15:07If you walk on damp sand, you'll leave a trace behind.
00:15:16A footprint.
00:15:18The same was true 66 million years ago.
00:15:23And very, very occasionally, such traces were preserved.
00:15:28And that's exactly what happened here at Tannis.
00:15:33You know, we won't foil the backside, we'll just put plaster right on.
00:15:38Robert has discovered a number of footprints.
00:15:41Yeah, let's see.
00:15:43Looks like a good print.
00:15:46Yeah.
00:15:48Their shape gives him a clue as to what might have made them.
00:15:56If he's right, they were made by a winged creature that might well have liked a small
00:16:06mammal for lunch.
00:16:18The footprints are long and narrow with four toe prints.
00:16:23Two are slightly longer than the others.
00:16:27And that suggests they were made by a pterosaur.
00:16:43Pterosaurs are not dinosaurs, but flying reptiles on a different branch of the evolutionary tree.
00:16:52Male pterosaurs usually had crests, while females didn't, so crests may have been used
00:17:11in courtship displays.
00:17:22And we have an indication of where females laid their eggs, because evidence suggests
00:17:28one pterosaur laid hers in the soft, sandy banks of the river at Tannis.
00:17:50And this is a fossilised egg of a pterosaur that Robert found there.
00:17:56The only one ever discovered in North America.
00:18:00If you look at it with the naked eye, all you see is a jumble of lines, but if you examine
00:18:07it with the latest technology, you can find out a wealth of information, from the chemistry
00:18:14of 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.
00:18:37It's a very powerful research tool that acts like a giant microscope.
00:18:44By accelerating electrons in this huge ring, the synchrotron creates beams of light many
00:18:50times brighter than the sun.
00:18:59Robert and paleobiologist Dr Victoria Edgerton now want to turn that beam onto the egg fossil
00:19:06to discover more about its chemical make-up.
00:19:10We're pretty much lined up on the skeleton, but we might have to move the stage a little
00:19:14bit to get to the right part.
00:19:16Sure.
00:19:17Meanwhile, Robert can reveal the creature inside.
00:19:23And this, who made this wonderful thing?
00:19:27I got replicas of the bones from inside that egg and I restored the remainder and put together
00:19:34what the skeleton would have looked like when it hatched.
00:19:37That's how big the creature would have been outside the egg, if it had hatched.
00:19:41So, this is the baby.
00:19:43How 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,
00:19:51because those long bones match very, very closely with the Asdarchid pterosaurs.
00:19:55That is the giant pterosaurs.
00:19:57Oh, they were the whoppers, weren't they?
00:19:59I mean, what, 25 feet wingspan?
00:20:03Some 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 fluttering out
00:20:15almost like a little bat.
00:20:22They've scanned the egg here and in America.
00:20:29Victoria has the results.
00:20:32So, what have you learnt from this cyclotron image?
00:20:36What we have here is a chemical map of calcium directly within the bones of this animal.
00:20:42That tells us that these bones were already hardened, so it might be ready to fly not
00:20:48long after it hatches.
00:20:50Okay.
00:20:51Can you see any sign of the shell and what sort of shell was it?
00:20:54We can.
00:20:55What 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.
00:21:08We 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.
00:21:26That's not the case, is it, with dinosaurs?
00:21:28Many dinosaurs had hard-shelled eggs.
00:21:30Yes.
00:21:31That's a new discovery about as dark as pterosaurs.
00:21:35Absolutely.
00:21:36This is something that we are confirming for the first time.
00:21:39Ah.
00:21:40So it's flying pterosaurs had eggs like turtles?
00:21:44Yes.
00:21:45Much more reptilian-like than bird-like.
00:21:48And that can potentially tell us more about the environment in which these eggs were laid.
00:21:53How interesting.
00:21:54Yeah.
00:21:55Creatures that lay soft eggs tend to bury them in order to protect them.
00:22:14So female pterosaurs probably looked for places like Canis to lay their eggs because the sandy
00:22:24soil here is just soft enough for the hatchling to dig itself out.
00:22:32Now the pterosaur just has to make sure that the hole is perfect.
00:22:57Success.
00:23:00But it's not over yet.
00:23:02Pterosaurs had two ovaries and they laid their eggs in pairs.
00:23:18Here on the sandbank, sandwiched between the river and these glorious trees, life at Canis
00:23:25seemed to be thriving.
00:23:28Whoops.
00:23:29Never a dull moment.
00:23:31But all that was about to change.
00:23:41The chain of events that led to the extinction of the dinosaurs began in the distant past,
00:23:47deep in space.
00:23:54Some scientists think it all started in a ring of dust, rocks and debris known as the
00:24:01asteroid belt.
00:24:05It's usually an uneventful place.
00:24:12But it's thought that many, many millions of years ago, a rock was bumped into a new orbit
00:24:23and diverted onto a collision course with planet Earth.
00:24:39Robert is building a vivid picture of late Cretaceous life at Canis.
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 river bank going down to drink at
00:24:59some point.
00:25:00You know, animals tend to congregate around the rivers.
00:25:04This print is 30 centimetres 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.
00:25:33I love this one.
00:25:39This is Robert's prize footprint.
00:25:42It has three toes.
00:25:45And it's longer than it is wide.
00:25:49So it's very likely to be a carnivorous dinosaur.
00:25:53It'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.
00:26:07This footprint is too small for an adult T. rex.
00:26:12But it's possible that it was made by a young one.
00:26:26Robert also found this at Tannis, the crown of a tooth.
00:26:33Its shape and its serrated edge are indications that it comes from an adult T. rex.
00:27:03Bite marks found on T. rex bones show that they ate other T. rexes.
00:27:12And 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.
00:27:37So if you find several in one place, as Robert has done, it's a reasonable assumption that
00:27:43there would have been many more nearby.
00:27:50And that supports the idea that dinosaurs and pterosaurs were thriving at Tannis shortly
00:27:57before the impact.
00:28:06And if they were thriving, they must have been reproducing.
00:28:21Fossils from dinosaurs similar to T. rex show they may have laid around 20 eggs in
00:28:27a circular nest.
00:28:35It's possible that, like crocodiles, they partly covered their eggs to keep them warm.
00:28:56For one T. rex, a misfortune.
00:29:07But for all dinosaurs, a disaster was looming.
00:29:26Deep in space, the asteroid was approaching.
00:29:35Its journey would take it to the orbit of our neighbouring planet, Mars.
00:29:46Had the two collided, a catastrophe on Earth would have been avoided.
00:29:59But it was not to be.
00:30:03And Earth's fate was sealed.
00:30:19As Robert's dig continues, his vision of what happened at Tannis is finally starting to
00:30:25come together.
00:30:28It 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.
00:30:44See the scales?
00:30:45I do.
00:30:46Oh my god.
00:30:47That excites me, just looking at it.
00:30:51Then Robert finds something truly remarkable.
00:30:58See the cracks already forming?
00:30:59Look at that.
00:31:00So we're going to have to really monitor that before we glue it, because this is getting
00:31:04vulnerable now.
00:31:05An almost complete creature.
00:31:11To get this block out, we're freezing it.
00:31:20Robert is about to attempt something tricky.
00:31:23Steady.
00:31:24Let's go.
00:31:25To get the fossil out in one piece, they're trying to freeze it using liquid nitrogen
00:31:35at almost 200 degrees below zero.
00:31:44Watch the footing.
00:31:45Lauren, I'm worried about brittleness here.
00:31:49Get that hammer.
00:31:50Give this a couple of whacks with the hammer.
00:31:53OK.
00:31:55Move over five centimeters.
00:31:56Good.
00:31:57It's cracked loose.
00:31:58Yep.
00:31:59OK, it's loose.
00:32:00So we have to get this out in one piece.
00:32:06One, two, three.
00:32:10Yeehaw!
00:32:12Total success.
00:32:15Total 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 now it's been cleaned up.
00:32:42It's lying on its side.
00:32:45Here's the outline of its shell.
00:32:49The shape of the shell and the scotched edges here tell us that this was a binid turtle.
00:32:59Robert's binid turtle looks very similar to modern cooter turtles
00:33:04and lived in the same sort of freshwater environment.
00:33:14For a turtle, Tannus would have been ideal.
00:33:22Warm, shallow water.
00:33:27Plenty to eat.
00:33:32And lots of safe places in which to warm up in the late Cretaceous sunshine.
00:33:42The turtle fossil Robert found is almost complete.
00:33:46This is the underside.
00:33:49And this brown material up here is fossilised 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 layer at Tannus.
00:34:16When I look at the animals and plants preserved in the sediments of Tannus and the footprints beneath it,
00:34:21I see a picture of a vibrant ecosystem, many different dinosaurs and a thriving, thriving place.
00:34:32After 10 years of digging, there is now enough evidence to piece together much of the story of Tannus and the creatures which lived here.
00:34:45Robert has found so many fossils, it looks as if even at the very end of the late Cretaceous, Tannus 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.
00:35:16Because all this was about to end.
00:35:21The asteroid hit in what is now the Yucatan Peninsula in Mexico.
00:35:50It's called the Chicxulub asteroid after the town nearest to the center of its crater.
00:36:16Any living thing within 900 miles of the impact was destroyed by the blast.
00:36:32But what effect did the impact have on Tannus nearly 2,000 miles away?
00:36:48To find out, Robert is looking for clues that might link Tannus to the actual day the asteroid hit.
00:37:02We've got some wood and pressed up against this and all intertangled we've got the carcasses of fish.
00:37:11That's a beautifully preserved tail, so that fish is going to be absolutely gorgeous.
00:37:16Part 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.
00:37:34In more ways than one, it literally is an operation of a Cretaceous fish, so we're performing surgery on this thing.
00:37:40Robert needs to open this fish's skull.
00:37:45Very 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.
00:38:00Got 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.
00:38:08Those are the bars that hold the filaments of the gills.
00:38:12And between the gill bars, all of these clusters of round objects, those are the ejecta spherules.
00:38:18Ejecta spherules are tiny balls that were once molten rock.
00:38:23They could be evidence of what Robert suspects, that creatures here died on the day of the asteroid strike.
00:38:31Those ejecta spherules last saw the light of day when they were flying through the air 66 billion years ago.
00:38:47After a large asteroid impact, a mix of vaporized and molten rock is propelled into space.
00:38:59It cools, solidifying into tiny glass droplets.
00:39:05Some carry on deeper into space.
00:39:10But most are pulled back to Earth by gravity.
00:39:21After a major asteroid hit, trillions of ejecta spherules 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.
00:39:37They'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 ejecta spherules, he finds more and more.
00:40:08And realizes the thick, crumbly layer of rock at Tannis is full of them.
00:40:16I mean, this stuff is gorgeous. Oh my God, look at that one. These things are just gorgeous.
00:40:22Ejecta spherules like this give us a fingerprint of where they came from.
00:40:28If these spherules were connected to the titular 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. Oh, 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.
00:40:48Oh my God, that's a beautiful droplet. Okay.
00:40:54The 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.
00:41:18It's a way for the tree to protect itself like a scab forming on a cut.
00:41:31Anything covered by the resin would be frozen in an amber time capsule.
00:41:38If they find a spherule preserved in amber, it could be analysed to see if it comes from the Chekshelob asteroid impact.
00:41:49So during this batch, we were incredibly lucky that we came across two completely unaltered spherules.
00:41:58This spherule could be something amazing.
00:42:03This spherule could be something amazing.
00:42:06Evidence preserved well enough to analyse for chemical clues.
00:42:14If so, it could link Tannis directly with the Chekshelob impact and the last day of the dinosaurs.
00:42:24To investigate, Robert is joined at the Diamond Light Source by Professor of Natural History, Phil Manning, of the University of Manchester.
00:42:35They've already run initial tests on the spherules in America.
00:42:40What have you found out so far?
00:42:42These little glass spherules, these globs of molten material from the impact site,
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 Chekshelob 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 Chekshelob 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 the sediments,
00:43:56are linked to the last day of the Cretaceous.
00:44:01And the synchrotron here in the UK reveals something even more remarkable.
00:44:08So this is showing a beautiful synchrotron scan of the half of one spherule.
00:44:15The glass is a good geochemical fingerprint, and we've got calcium, some iron, we've got strontium.
00:44:23But when we look at the entire thing, we see something quite unexpected.
00:44:28That's your entire spherule.
00:44:31What'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.
00:44:44A 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 Chichibu asteroid.
00:45:14The piece of the bullet that killed the dinosaurs.
00:45:17No.
00:45:24Robert could have found a fragment of the asteroid itself in Tanis.
00:45:30Physical evidence linking this site to the Chicxulub impact.
00:45:35But Tanis 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 lair.
00:45:55Right here, we've got this intertangled mass of fish.
00:45:59There'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
00:46:08and 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
00:46:22surrounded by spherules and crushed together in what's known as a log jam.
00:46:28He has a theory that the creatures were swept to their death
00:46:32in some kind of turbulent surge of water and quickly entombed in sediment,
00:46:37which is why they're so well preserved.
00:46:40But what could have caused the wave?
00:46:47One theory is a tsunami.
00:46:53The asteroid hit at sea.
00:46:56Recent studies show it may have caused the wave almost a mile high.
00:47:15The height of the wave would have gradually reduced as it spread across the oceans.
00:47:21In the late Cretaceous, North America was divided by a narrow sea
00:47:26that's been called the Western Interior Seaway.
00:47:29The tsunami could have travelled up this towards Tannis.
00:47:37But there's a big question about the tsunami idea.
00:47:41The timing.
00:47:44Oh, which fish is that? It's a new contact.
00:47:49If a tsunami killed the fish,
00:47:52it would have to have hit while ejecta spherules were falling,
00:47:57because spherules were found in the fish's gills.
00:48:03So how long after impact did the spherules arrive at Tannis?
00:48:08Pretend this ball of foil is a piece of ejecta coming out of the crater.
00:48:12It would then go on an arc path, ballistic trajectory,
00:48:15out of the crater and to wherever it lands, in this case Tannis.
00:48:21If we know the distance between myself and the landing site,
00:48:24and if we know the size of that ball,
00:48:27we can accurately calculate how long it would take to get there.
00:48:34The result is surprising.
00:48:36Robert and his team calculated that these ejecta spherules
00:48:40landed at Tannis between 13 minutes and two hours after the impact.
00:48:48If 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
00:49:03to travel almost 2,000 miles from the impact site to Tannis.
00:49:10So if it wasn't a tsunami, what could have caused the surge of water at Tannis?
00:49:25Professor Stein Bondevik is an expert in tsunamis.
00:49:34The fjords in Norway are very special.
00:49:38We have tall mountains surrounding bodies of water,
00:49:42so the water is usually very calm.
00:49:46In 2011, something very strange happened.
00:49:50The water in the fjord began to move violently.
00:49:55The height of the water increased by one and a half meter.
00:49:59Like a maelstrom with turbulent water,
00:50:03someone said that the fjord was boiling.
00:50:08News started to roll in.
00:50:10There'd been an earthquake 5,000 miles away in Japan.
00:50:17A journalist from the local newspaper called me and he said that
00:50:21people were observing waves here in the fjords.
00:50:26I got a video clip of the waves.
00:50:29I saw immediately that they looked like a tsunami wave.
00:50:33So later in the afternoon, you can see that the fjord is perfectly calm.
00:50:39But at the beach here, you can see that the water is sloshing back and forth.
00:50:43And no one had ever seen anything like it.
00:50:48Some people got very upset and afraid.
00:50:54A magnitude 9 earthquake had devastated the northeast of Japan around Fukushima.
00:51:04But how did that affect a fjord so far away?
00:51:10So no one in Norway could feel the earthquake.
00:51:14But I could see that the times matched the arrival of the waves here in the fjord.
00:51:24Eventually, Stein and his team realised that this might have something to do with seismic waves,
00:51:31shock waves that pass quickly through the earth during an earthquake.
00:51:37So it took only 12 minutes before the first signal of the earthquake in Japan
00:51:41reached all the way here to western Norway.
00:51:47So it was these seismic waves that caused the normally calm water in the fjord
00:51:52to slosh turbulently back and forth.
00:51:56Just thinking of that, scientifically, it's fantastic.
00:52:07Could something similar have happened in Tannis?
00:52:16Trying to find out is geophysicist Professor Mark Richards,
00:52:21who's been studying the site at Tannis for several years.
00:52:26He's working with Robert to discover what could have caused a surge of water here.
00:52:38A tsunami can't get here in less than, minimum, 12 hours.
00:52:43But seismic waves travelling from the Yucatan impact site to North Dakota
00:52:48can arrive here fairly quickly.
00:52:52In the late Cretaceous, the western interior seaway that divided North America
00:52:58could have been connected to Tannis through a system of rivers.
00:53:07If you have a very large body of water, like the western interior seaway,
00:53:13and you can shake it back and forth,
00:53:15you can generate a large water wave coming up this river at Tannis.
00:53:25So seismic waves from the impact could have caused surges of water in the Tannis River system.
00:53:33Seismic waves get here quickly enough, coming up the Tannis River,
00:53:38inundating this area, arriving at the same time these spherules are still falling out of the air.
00:53:46The mystery of the wave and the thick layer of crumbly rock has been solved.
00:53:53Seismic waves travelling through the earth could have caused powerful surges of water at Tannis,
00:54:02possibly carrying mud and marine creatures like ammonites from the western interior seaway,
00:54:09dumping them on the Tannis sandbank and burying everything at the same time as spherules fell.
00:54:25Over millions of years, the mud would turn into the layer of crumbly rock.
00:54:32And that's the beauty of Tannis.
00:54:34And that's the beauty of Tannis.
00:54:37What you're seeing is a deposit that is literally recording the last, say, 45 minutes to an hour and a half of the Cretaceous.
00:54:58If the extinction of the dinosaurs was a crime,
00:55:01the 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.
00:55:20But they would be missing one very important thing.
00:55:24A body.
00:55:25A body.
00:55:30No one has ever found the fossil of a dinosaur that was killed by the effects of the asteroid impact.
00:55:39But Robert did find part of a triceratops in the crumbly layer at Tannis.
00:55:45So could that be the remains of a dinosaur that died on that day?
00:55:50I'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.
00:56:10This 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, they wondered whether it had been killed in a fight.
00:56:36But when they looked at the fractures in more detail, they found signs of new bone growth here.
00:56:43An indication that the bone had started to heal.
00:56:46So 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 of the skin, which 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.
00:57:24Perhaps in the months before the impact, the broken horn put the triceratops at a disadvantage over its rivals.
00:57:47And that might have led to starvation.
00:57:50Robert has still not found direct evidence of a dinosaur that was killed by the asteroid.
00:58:19We've got all these bones in the ground right now, but the one thing that we would just dream of finding is that one dinosaur that died on the day of the impact.
00:58:32And the weather isn't helping his search.
00:58:35Wow.
00:58:51That theropod print is toasted.
00:58:54Yeah, it was in a low corner.
00:58:56It's full of mud and water.
00:58:59The problem is it's wet.
00:59:00Look, see, if we're not careful, we're going to lose the print.
00:59:04And that's the biggest theropod print we've got.
00:59:07I see some areas that could use glue right now, too.
00:59:13The team is racing to excavate the footprints, along with dozens of fish fossils tangled together in a log jam before storms wash them away.
00:59:25We're up against the clock here.
00:59:26The stuff that could be exposed right now is going to get ruined by the rain.
00:59:32But then, Robert comes across something that looks very unusual.
00:59:40What is going on right there?
00:59:42Are we sure this isn't crocodilian?
00:59:44That's not crocodilian.
00:59:46No.
00:59:47I'm going to try this piece right here.
00:59:49I'll go in from the top and then twist up, and it separates off right on that line.
00:59:53That's skin right there.
00:59:55That's actually scaly skin.
00:59:57No, no, no, no, no.
00:59:58Look, look, look.
00:59:59Look at that pattern right there.
01:00:01Have you ever seen elongated scales like that before, Dave?
01:00:04Scutellates and birds.
01:00:06Just careful.
01:00:09It's changing again.
01:00:10It's changing again.
01:00:13We're seeing it for the first time in 66 million years.
01:00:16I think we've got ourselves a dinosaur.
01:00:19A dinosaur fossil.
01:00:21And unlike the Triceratops, this is located in the log jam, the mass death lair,
01:00:28surrounded by the fish with spherules in their gills.
01:00:35This is the most incredible thing that we could possibly imagine here,
01:00:38the best-case scenario.
01:00:40We're in the middle of a desert.
01:00:42We're in the middle of a desert.
01:00:44We're in the middle of a desert.
01:00:45This is the most incredible thing that we could possibly imagine here,
01:00:47the best-case scenario.
01:00:49We're excavating this mass death lair of fish from the surge sent up by the impact,
01:00:54and 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.
01:01:02This is unreal.
01:01:04I cannot process this in my brain.
01:01:06I am absolutely blown away by this.
01:01:08Just my heart is literally pumping out of my chest,
01:01:11wondering what is behind there, just a couple centimeters back in the outcrop.
01:01:13What is waiting for us back there?
01:01:20The team keeps digging.
01:01:24So this could be a rib cage.
01:01:26It could be laying against ribs that are curved.
01:01:28There's something here.
01:01:30That's hard.
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...
01:01:44And we can go from the thigh of the animal.
01:01:47There's the knee,
01:01:49and then you've got the little calf muscles of the dinosaur there bulging out,
01:01:54and you go down to the ankle bones,
01:01:56and these are the toes of the feet.
01:01:59We've got nails at the tips of the toes.
01:02:01It's a beautifully preserved leg, all articular.
01:02:03It's covered with skin.
01:02:05The complete leg of a dinosaur.
01:02:09In my wildest dreams,
01:02:11I never expected to find a dinosaur leg in this deposit.
01:02:14And then it's got skin and tissue.
01:02:16It does look just like a drumstick.
01:02:19It looks like a Thanksgiving turkey just laid out on the ground.
01:02:22And this weird scale pattern on the thigh of the animal,
01:02:26which we've never seen in a dinosaur before.
01:02:29Well, it's not a dinosaur.
01:02:30Thessaurs don't have any form of defense,
01:02:32so they have to have camouflage or something.
01:02:34That's a good point.
01:02:36So this could have been some sort of camouflage marking.
01:02:38Yeah.
01:02:40Robert thinks he has found the body in question.
01:02:44A dinosaur that might itself have witnessed the cataclysmic impact.
01:02:53Dinosaur fossils are not known from the last years of discovery.
01:02:57Dinosaurs are not known from the last years of the Cretaceous.
01:03:01And it was unclear whether they were already extinct or in decline,
01:03:05or what was going on.
01:03:07So they were just sort of absent.
01:03:11And this answers that question.
01:03:13Were dinosaurs still there then?
01:03:15Well, yes.
01:03:17This one likely died in that surge.
01:03:20For such big claims, Robert needs verification.
01:03:28He's brought the dinosaur leg to London to get a second opinion.
01:03:33And then here are the pads of the toes.
01:03:36We see all those beautiful scales lined up.
01:03:38From Professor Paul Barrett,
01:03:41an expert in Ornithischian dinosaurs from the Natural History Museum.
01:03:46So what do you think this might be?
01:03:48When we look at the leg, it has claws,
01:03:51like the claws we see in small, agile, bipedal running dinosaurs that are plant eaters.
01:03:58We can rule out things like Triceratops,
01:04:00partly just because it's not big and stocky.
01:04:03And the proportions of those legs are also different from some of the other plant eaters we see,
01:04:08in that they have this rather long ankle and shin,
01:04:11compared with its thigh bone,
01:04:12so as we narrow those possibilities down,
01:04:15what we're left with, probably, is an animal called a Thessalosaur.
01:04:27Thessalosaurs lived next to rivers where there was plenty of rich vegetation to feed on.
01:04:35They had leaf-shaped teeth, common amongst herbivores.
01:04:39And claws on their short front limbs.
01:04:42Excellent for digging.
01:05:03But how did Robert's Thessalosaur die?
01:05:05Could it have been killed by another dinosaur?
01:05:08It's a possibility.
01:05:10This is a relatively agile animal.
01:05:12And that turn of speed would have been its primary defence against the large predators living alongside it.
01:05:24So, to escape a hungry T. rex,
01:05:27a Thessalosaur's first line of defence
01:05:30is to eat its prey.
01:05:32A Thessalosaur's first line of defence
01:05:36would have been to run.
01:05:40But it may have had another defensive trick.
01:05:52Living next to rivers, it's possible Thessalosaurs were able to swim.
01:06:03Thessalosaurs
01:06:11It doesn't seem to me like there is any evidence that this animal was predated.
01:06:16None of the obvious tooth marks or left-over bits of carnivore teeth to suggest it's been eaten.
01:06:22So, how do you think it died?
01:06:24It didn't have any particularly nasty diseases when it died.
01:06:28As we can see, the bones look OK.
01:06:29So, this is an animal that was probably living and healthy at the time that this happened to it.
01:06:35Could 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.
01:06:48And similarly, this little bone here
01:06:50would have been from about maybe a third of the way along the tail, maybe halfway down.
01:06:55So, somehow, these two bones have been telescoped together.
01:06:59So, maybe this animal has been tumbled around.
01:07:02We've ruled out a lot of other possible causes of death for this animal.
01:07:07So, it could well be that this is an animal that was there,
01:07:10being tumbled around in its death throes 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. And 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, and there it is, ready to be dug up.
01:07:36Wow.
01:07:50After years of investigation,
01:07:52Robert has found out a great deal about the creatures which lived at Tannus.
01:07:56And he knows that many of them were alive on that fateful day
01:08:01when the asteroid devastated our planet.
01:08:04But how exactly did they die?
01:08:08Robert's finds now allow us to tell the story of that day
01:08:12and finally answer that question.
01:08:18One of the most important days in Earth's history
01:08:22probably started much like any other late spring morning.
01:08:26We know the season because Robert found fossils of young fish
01:08:36that died at the size they reach at that time of year.
01:08:39This agrees with evidence already found by other scientists.
01:08:46Perhaps this day, that would end with so much death,
01:08:50began with something different.
01:08:54A new life.
01:08:56A new life.
01:09:19No one can be certain of the exact timings of the day
01:09:23when the asteroid collided with our planet.
01:09:26It's estimated that within just 40 minutes of the impact,
01:09:30the consequences for the creatures of Tannus would have been profound.
01:09:38Based on Robert's finds and the latest evidence from other scientists,
01:09:42this is how the catastrophe might have unfolded.
01:09:48The asteroid is around seven miles across,
01:09:52bigger than Mount Everest.
01:09:54And travelling at close to 45,000 miles an hour.
01:10:02The impact causes an explosion bigger than a billion Hiroshima atomic bombs.
01:10:16At Tannus, almost 2,000 miles away,
01:10:20it's completely silent.
01:10:26But at the impact site,
01:10:30the asteroid vaporises.
01:10:34More than three trillion tons of rock are ejected into space
01:10:39in a blast of superheated violence.
01:10:42Winds higher than 600 miles an hour.
01:10:47A colossal earthquake, followed by a ring of massive tsunamis.
01:11:01All the while, the creatures at Tannus go about their business.
01:11:05Just like any other day.
01:11:36The evidence suggests that baby pterosaurs emerged from the egg
01:11:41ready to fend for themselves.
01:11:45And that includes...
01:11:49flying?
01:11:52Well, almost.
01:11:55Elsewhere, as the devastation spreads out across North America towards Tannus,
01:12:02dinosaurs and creatures of all shapes and sizes are obliterated by the blast.
01:12:25At Tannus, for a few more precious minutes, life carries on as usual.
01:12:32But the clock is ticking.
01:12:48The blast from the impact never reaches Tannus,
01:12:51but seismic shockwaves do.
01:13:06They are far more powerful than any earthquake ever recorded.
01:13:22The Thessalosaur might head for a place of safety.
01:13:30But seismic waves are now slowly shaking the whole region,
01:13:34causing water to slosh and churn.
01:13:42At Tannus, strange currents in the river give a hint of what is still to come.
01:13:52Next, it begins to rain.
01:13:57Dejecta spherules are falling back to Earth.
01:14:10As the spherules begin their fall,
01:14:14friction heats them until they're red-hot.
01:14:18Then, the heat transfers to the air.
01:14:23Temperatures rise with every second.
01:14:33As the heat builds, the creatures of Tannus are fighting for their lives.
01:14:39And then, as seismic waves continue to slowly rock the whole region,
01:14:48a violent surge wave, 10 metres high, rushes up the Tannus River.
01:14:57The Tannus River is now at an all-time high.
01:15:01A violent surge wave, 10 metres high, rushes up the Tannus River.
01:15:07Surviving the turbulence of the surge is a challenge even for the best swimmers.
01:15:38Then, the powerful rocking of the river system slowly begins to draw the water back the way it came.
01:15:56Swimming may have saved the Thessalosaur in the past,
01:16:00but not this time.
01:16:08A large, robust animal like a T-Rex might have survived the surge,
01:16:19as might a hard-shelled reptile.
01:16:23But there is much more to come.
01:16:26As billions of tonnes of superheated spherules continue to fall,
01:16:31the atmosphere gets even hotter.
01:16:33Igniting dead leaves and sparking wildfires.
01:16:45Earthquakes.
01:16:47Fire.
01:16:50Devastation.
01:16:54Little would survive for long.
01:16:57On land, on water,
01:16:59little would survive for long.
01:17:02On land,
01:17:08or in the air.
01:17:30As the air reaches the temperature of an industrial oven,
01:17:37those that live deep underground may have a better chance.
01:17:48As the slow sloshing of the river system continues,
01:17:55another powerful surge hits.
01:18:00The T-Rex.
01:18:18There is no escaping the destruction.
01:18:22For many of the creatures of Tannis, their stories end underwater.
01:18:43In less than two hours, the world has changed forever.
01:18:52The mud the surge waves leave behind
01:18:56will gradually turn into the thick layer of crumbly rock
01:19:00entombing the creatures which died here.
01:19:05Until 66 million years later,
01:19:09when they are finally unearthed.
01:19:22Robert's finds have helped us understand in remarkable detail
01:19:27what happened at Tannis in the minutes after the asteroid impact.
01:19:32But what about the rest of the world?
01:19:37The impact triggered catastrophic events
01:19:41such as earthquakes all over the planet.
01:19:45And as spherules continued to fall,
01:19:51wildfires may have sprung up around the globe.
01:19:57As that horrific day drew to a close,
01:20:00many of the world's dinosaurs were already dead.
01:20:09Research shows that the angle at which the asteroid hit
01:20:14and the sulphur-rich rocks at the impact site
01:20:17amplified the devastation.
01:20:19Billions of tonnes of sulphur were ejected into the atmosphere,
01:20:24blocking the sunlight.
01:20:27Without light, most plants died and food became scarce.
01:20:34As the weeks and months passed,
01:20:37any dinosaur left alive would have died of hunger.
01:20:43In the oceans, it was the same.
01:20:45Nearly all of the world's plankton disappeared,
01:20:49leading to the starvation of most marine creatures.
01:20:54It's thought that the nuclear winter that followed
01:20:58caused 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,
01:21:12including the dinosaurs.
01:21:14The planet was in semi-darkness for around a decade,
01:21:19as dust and soot slowly fell to Earth.
01:21:24But then came something wonderful,
01:21:28a new beginning.
01:21:34Once the dust cleared from the atmosphere and the sunlight returned,
01:21:38plant life was gradually restored,
01:21:41led by ferns, the spores of which had lain dormant deep underground.
01:21:48And the world began to turn green once more.
01:21:53But what about the animals?
01:21:58Back at Tannis, Robert has unearthed something
01:22:02that could have helped save the dinosaurs.
01:22:04Back at Tannis, Robert has unearthed something
01:22:07that could have helped save some of the creatures from the devastating fires.
01:22:12We saw a little thing poking out, so we kind of followed it back,
01:22:16and I'm so glad that we did,
01:22:18because what we have here is a fossil burrow
01:22:21from an animal 66 million years ago.
01:22:24The only animals that would have been around back then
01:22:27that would likely build a burrow like this
01:22:30would be the small mammals, roughly ferret-sized,
01:22:32and also some reptiles.
01:22:34If it is from a mammal,
01:22:36this is sort of a window into the lifestyle
01:22:39of some of our oldest ancestors out here.
01:22:42This guy would have burrowed sideways, right into the riverbank.
01:22:47I actually have some scratch marks on there
01:22:50from the interior when they were digging it, going back.
01:22:53And he would have lived back here and sought shelter from the dinosaurs,
01:22:56because they just did not want to get eaten.
01:23:03Burrows are part of the reason that mammals survived the Great Extinction.
01:23:10During the nuclear winter,
01:23:13a burrow would have provided warmth, protection,
01:23:16and a place to store food.
01:23:25Mammals that survived were resourceful omnivores,
01:23:29and insects would have been a plentiful source of food.
01:23:33And they had another advantage.
01:23:36Their size.
01:23:39If conditions are right,
01:23:41many animal species get larger as they evolve over millions of years.
01:23:46Take T. rex as an example.
01:23:49This is a cast of the lower jaw of a predecessor called Gorgosaurus,
01:23:55which lived to be about two and a half million years old.
01:23:57This is a cast of the lower jaw of a predecessor called Gorgosaurus,
01:24:02which lived 72 million years ago.
01:24:05Whereas this is the cast of the lower jaw of a T. rex,
01:24:11which lived five million years later.
01:24:14Look at the difference in size.
01:24:17But the bigger the creature, the more energy they need to stay alive.
01:24:21So when catastrophe strikes and food is scarce,
01:24:25the largest tend to die out.
01:24:27Whilst the smallest often survive.
01:24:33That's one of the reasons why many of the smaller mammals
01:24:37lived through the great darkness.
01:24:40And they weren't alone.
01:24:44Robert's fossil turtle may have been unlucky,
01:24:48but many others survived.
01:24:50As did crocodiles, snakes, and many fish species.
01:24:58And as for the dinosaurs, did the impact really kill them all?
01:25:03Well, this beautiful fossilised feather isn't from a bird,
01:25:09but from a predatory dinosaur.
01:25:12So we have to be careful when we say that dinosaurs are extinct,
01:25:15because what we call birds originally evolved
01:25:20from the smallest feathered dinosaurs.
01:25:23So to be correct, we should say all non-avian dinosaurs are extinct.
01:25:31Robert's finds have given us a better idea than ever before
01:25:37about what happened on the day that led to the extinction of dinosaurs.
01:25:42What happened on the day that led to the extinction
01:25:47of the largest beasts ever to walk the Earth.
01:25:54Dinosaurs were perhaps some of nature's most extraordinary creatures,
01:26:00dominating the planet for over 150 million years
01:26:04before they became extinct.
01:26:08But extinction comes in different forms.
01:26:10And many of the amazing creatures and plants alive today are also threatened.
01:26:16It's possible that humanity is having as big an impact on the world
01:26:21as the asteroid that ended the age of the dinosaurs.
01:26:26As human beings, we are unique in our ability to learn from the distant past.
01:26:32Now we must use that ability wisely
01:26:35and do our very best to protect the millions of species
01:26:39for whom, alongside us, this planet is home.
01:26:44Animals fighting for their families against the odds.
01:26:48Watch Dinnisters 2 with David Attenborough.
01:26:51That's on BBC iPlayer now.
01:26:53Former manager of the Royal Society of Dinosaurs,
01:26:56David Attenborough,
01:26:58is now the head of the Royal Society of Dinosaurs.
01:27:01He's been a member of the Royal Society of Dinosaurs
01:27:04for over 50 years.
01:27:06He's been a member of the Royal Society of Dinosaurs
01:27:09for over 50 years.
01:27:10David Attenborough.
01:27:12That's on BBC iPlayer now.
01:27:14Former MasterChef champions are back,
01:27:16but this time they're hungry.
01:27:18New MasterChef.
01:27:20That follows next here on BBC One.
01:27:22And hold on tight.
01:27:24Searching for the best tractor drivers.
01:27:26It's the fast and the farmer-ish on BBC Three.