0:00:07 > 0:00:10Two and a half million years ago,
0:00:10 > 0:00:15life on Planet Earth faced the dawn of a new era...
0:00:22 > 0:00:23..the Ice Age.
0:00:27 > 0:00:29Now we can go back in time...
0:00:32 > 0:00:36..because out of the permafrost,
0:00:36 > 0:00:40from deep inside caves,
0:00:40 > 0:00:44and from hostile deserts,
0:00:44 > 0:00:48the astonishing remains of giant animals are emerging.
0:00:50 > 0:00:54How amazing to be one of the first people to see this ancient creature.
0:00:57 > 0:01:03The Ice Age was the last time such creatures would walk the Earth.
0:01:05 > 0:01:10A lost Eden with mammoths taller than any elephant,
0:01:10 > 0:01:15cats with seven-inch teeth,
0:01:15 > 0:01:19and some of the strangest beasts that have ever existed.
0:01:19 > 0:01:24I'm fascinated by what the remains of ancient animals can tell us
0:01:24 > 0:01:29about THEM, and the world they lived in.
0:01:29 > 0:01:34Using new scientific advances, we can reveal how they lived,
0:01:34 > 0:01:37and why they died out.
0:01:44 > 0:01:48Come with me, back to the Ice Age.
0:01:51 > 0:01:53A world ruled by giants!
0:02:18 > 0:02:23The Great Ice Age was triggered by a combination of natural forces
0:02:23 > 0:02:27acting on a colossal scale.
0:02:27 > 0:02:30Continents moved.
0:02:30 > 0:02:34The planet shifted in its orbit.
0:02:34 > 0:02:40Earth was battered by a merciless cycle of freeze and thaw.
0:02:44 > 0:02:48The last freeze started around 80,000 years ago.
0:02:56 > 0:03:00A vast ice sheet marched down from the Arctic,
0:03:00 > 0:03:05across a continent that today we call North America.
0:03:11 > 0:03:16Known as the Laurentide Ice Sheet, it wiped out everything in its path.
0:03:16 > 0:03:18It advanced down over the continent,
0:03:18 > 0:03:21and life retreated before it.
0:03:21 > 0:03:25No animals or plants could survive on its endless icy plains.
0:03:28 > 0:03:31It might seem like a catastrophe,
0:03:31 > 0:03:33but beyond the ice, incredibly,
0:03:33 > 0:03:36the continent saw an explosion of life...
0:03:44 > 0:03:47..making America the best place in the world
0:03:47 > 0:03:49to discover long-lost giants.
0:03:58 > 0:04:02I'm going south of where the ice sheet once lay,
0:04:02 > 0:04:07searching for megafauna - the great beasts of the Ice Age.
0:04:12 > 0:04:17Where else would you go for an encounter with the ultimate Ice Age celebrity?
0:04:19 > 0:04:23This is the territory of one of the most iconic
0:04:23 > 0:04:26and terrifying animals of the Ice Age.
0:04:26 > 0:04:28This is Los Angeles.
0:04:36 > 0:04:40A place with a surprisingly deep past.
0:04:40 > 0:04:44This glittering city, today the home of movie stars
0:04:44 > 0:04:49and billionaires is also a portal to a lost world.
0:04:49 > 0:04:52Here, we can step back in time
0:04:52 > 0:04:55and meet this awesome creature face to face.
0:05:00 > 0:05:04Smilodon fatalis, a sabre-tooth cat,
0:05:04 > 0:05:07surveys her territory...
0:05:08 > 0:05:10CAT GROWLS
0:05:12 > 0:05:17..some of the richest hunting grounds in the Ice Age world.
0:05:20 > 0:05:21CAT ROARS
0:05:27 > 0:05:32There is something primal and nightmarish about these teeth.
0:05:34 > 0:05:38But exactly how they were used has been a mystery.
0:05:42 > 0:05:48You can't help but be impressed by this fantastic skull and these formidable teeth,
0:05:48 > 0:05:52but this construction presented Smilodon with a problem.
0:05:52 > 0:05:55These teeth are so long and thin
0:05:55 > 0:05:59that they're actually very vulnerable.
0:05:59 > 0:06:02If they were to get stuck in the sinews or the bone
0:06:02 > 0:06:05of a violently struggling animal,
0:06:05 > 0:06:07there's a real danger they could snap.
0:06:14 > 0:06:18It's certainly not a problem faced by any large predator today.
0:06:32 > 0:06:37The big cats of the African plains kill large prey by suffocation.
0:06:41 > 0:06:42Either by smothering...
0:06:46 > 0:06:48..or by crushing the windpipe.
0:06:57 > 0:07:02Remarkably, the canines of a lion rarely even break the skin.
0:07:09 > 0:07:13But Smilodon could not have killed in this way.
0:07:21 > 0:07:28Blaire Van Valkenburgh has spent decades puzzling it out.
0:07:28 > 0:07:33Her evidence points to a method of killing unique to sabre-tooth cats.
0:07:36 > 0:07:39Their teeth were used for stabbing.
0:07:41 > 0:07:44What we THINK is that they went for
0:07:44 > 0:07:49the throat because there is a lot of structures in there
0:07:49 > 0:07:50that make you quite
0:07:50 > 0:07:55vulnerable, such as your windpipe, or jugular vein or carotid arteries,
0:07:55 > 0:07:59these mass of arteries that feed blood to the brain.
0:08:03 > 0:08:07But Blaire needed to figure out how a sabre-tooth cat could
0:08:07 > 0:08:09safely deliver this stabbing death blow.
0:08:16 > 0:08:20How does its skull compare with other big cats?
0:08:26 > 0:08:30A CT scan reveals that the temporal bone, where the jaw
0:08:30 > 0:08:36joins the skull is incredibly thick in a sabre-tooth cat,
0:08:36 > 0:08:40much thicker than in a lion or a cheetah.
0:08:40 > 0:08:45That means a chillingly powerful bite
0:08:45 > 0:08:47and massive jaw muscles.
0:08:50 > 0:08:52To land that lethal bite,
0:08:52 > 0:08:55their mouths could open wide,
0:08:55 > 0:08:58twice as wide as any lion.
0:09:04 > 0:09:08With these canines, they could drive these two things together
0:09:08 > 0:09:09and then pull backwards...
0:09:18 > 0:09:22..and take out a large amount of flesh...
0:09:24 > 0:09:27..making the animal probably bleed to death within minutes.
0:09:30 > 0:09:35A brutal technique that few animals could defend against.
0:09:46 > 0:09:49An American horse.
0:09:49 > 0:09:56To despatch it, this cat must go in hard and kill quickly.
0:09:56 > 0:09:58It's at the moment of the kill
0:09:58 > 0:10:01that the cat's teeth are at their most vulnerable.
0:10:04 > 0:10:08The secret to protecting them lies in its bones.
0:10:13 > 0:10:16Usually what we see in association with having big canine teeth
0:10:16 > 0:10:19like that in these kinds of sabre-toothed species
0:10:19 > 0:10:22is their sort of over-muscled forelimbs.
0:10:22 > 0:10:25They have very heavy, strong forelimbs, like wrestlers.
0:10:25 > 0:10:30And pig paws, too. Their paws are enlarged with big dewclaws, here
0:10:30 > 0:10:34and then they could grasp the prey and hold it steady,
0:10:34 > 0:10:37one paw holding the head, one holding the body,
0:10:37 > 0:10:40and then apply this killing bite, just where they need to put it
0:10:40 > 0:10:45and thereby minimise the risk to themselves of breaking those teeth.
0:10:52 > 0:10:55With these incredibly powerful forelimbs, it would pull down
0:10:55 > 0:10:58its prey before dispatching it
0:10:58 > 0:11:01with these terrifying teeth.
0:11:17 > 0:11:18PREY NEIGHS
0:11:21 > 0:11:22CAT ROARS
0:11:27 > 0:11:31Everything about a sabre-toothed cat, its teeth,
0:11:31 > 0:11:34its killing technique and its muscular body,
0:11:34 > 0:11:41point to one thing - this predator was designed to hunt large prey.
0:11:49 > 0:11:50During the Ice Age,
0:11:50 > 0:11:55sabre-tooth cats flourished right across the continent.
0:11:55 > 0:12:00So America must been full of large animals for them to hunt.
0:12:08 > 0:12:13My next giant may not be as famous as its sabre-toothed predator
0:12:13 > 0:12:18but for me, it's even more extraordinary.
0:12:18 > 0:12:23It inhabited the most spectacular part of America.
0:12:23 > 0:12:28I'm looking for Ice Age secrets in the desert landscape
0:12:28 > 0:12:30of the Grand Canyon.
0:12:32 > 0:12:37This creature left behind something far more revealing
0:12:37 > 0:12:40than just its teeth and bones.
0:12:51 > 0:12:56Hidden somewhere high up amongst these towering walls
0:12:56 > 0:12:59and spires is its lair.
0:13:15 > 0:13:16Thank you!
0:13:25 > 0:13:30Nothrotheriops shastensis - the Shasta ground sloth.
0:13:32 > 0:13:34As large as a grizzly bear.
0:13:42 > 0:13:46She walks on the sides of her feet,
0:13:46 > 0:13:49ponderous as she browses.
0:14:07 > 0:14:11But she has seven-inch-long claws.
0:14:11 > 0:14:14Too dangerous - even for a sabre-tooth.
0:14:14 > 0:14:17THEY ROAR
0:14:28 > 0:14:31With such a huge body to feed,
0:14:31 > 0:14:34she isn't really what you'd expect to find in a desert.
0:14:43 > 0:14:47Jim Mead is a world expert in ground sloths.
0:14:47 > 0:14:50He'll help me track it down.
0:14:57 > 0:15:00Today, in the Grand Canyon,
0:15:00 > 0:15:04a lot of the plants here are either poisonous
0:15:04 > 0:15:09or, like this jumping cholla cactus, covered in vicious spines.
0:15:13 > 0:15:16The hideous spines of the barrel cactus were even used
0:15:16 > 0:15:20by the Aztecs for sacrificing victims.
0:15:24 > 0:15:30A clue as to how the ground sloth survived here lies within its lair.
0:15:36 > 0:15:40To find it, we have to retrace the animal's journey,
0:15:40 > 0:15:44right up into the high canyon walls.
0:15:47 > 0:15:50Are we nearly there yet, Jim?
0:15:50 > 0:15:51A long way!
0:16:08 > 0:16:12As our eyes adjust to the gloom of the cave,
0:16:12 > 0:16:15I can't quite believe what I'm seeing.
0:16:20 > 0:16:24So Jim - what is this, is this what it looks like?
0:16:24 > 0:16:27This is just a pile of dung of a Shasta ground sloth,
0:16:27 > 0:16:31an extinct animal of the Ice Age, and we have a whole pile of it here.
0:16:31 > 0:16:34I just find it utterly unbelievable
0:16:34 > 0:16:37that this ancient animal's faeces are still here.
0:16:37 > 0:16:41I mean, that looks like a piece of relatively fresh dung
0:16:41 > 0:16:43which has just been dried out.
0:16:43 > 0:16:45Why on earth hasn't it rotted away?
0:16:45 > 0:16:47There's no water. It's a totally dry cave.
0:16:47 > 0:16:49And so without the water,
0:16:49 > 0:16:51you don't get the decay to mumify it.
0:16:51 > 0:16:54And it's preserved, and it's preserving
0:16:54 > 0:16:57a very unique record of this animal.
0:16:59 > 0:17:02You can see all these definite twigs.
0:17:02 > 0:17:06It's not a good digester. It's doing a very poor job of digesting,
0:17:06 > 0:17:09which is wonderful for us, cos here's the data.
0:17:11 > 0:17:17It's incredible to be holding the remains of a meal,
0:17:17 > 0:17:22eaten by this giant animal, during the Ice Age.
0:17:22 > 0:17:26The dung reveals that the sloth's menu was richer than
0:17:26 > 0:17:28what's on offer today.
0:17:28 > 0:17:34There were also juniper and single-leaf ash trees growing here.
0:17:34 > 0:17:38But it's still a big challenge for any digestive system.
0:17:44 > 0:17:48A clue as to how the ground sloth survived
0:17:48 > 0:17:50lies with its relatives -
0:17:50 > 0:17:53the ones that didn't go extinct.
0:17:53 > 0:17:55A tree sloth.
0:17:55 > 0:17:59She lives high up in the canopy of the South American rainforest...
0:18:01 > 0:18:04..dining on tough and toxic leaves.
0:18:07 > 0:18:10It will take her weeks to digest them,
0:18:10 > 0:18:12and for precious little energy...
0:18:16 > 0:18:20..which is why sloths are so terribly slow.
0:18:29 > 0:18:32The ground sloths of the Ice Age
0:18:32 > 0:18:36were adapted for THEIR strange diets, too.
0:18:36 > 0:18:39If you could peer inside a ground sloth,
0:18:39 > 0:18:42you'd see a huge fermenting gut.
0:18:45 > 0:18:52A Shasta ground sloth was basically a compost heap on legs.
0:18:52 > 0:18:55It could digest pretty much anything.
0:18:57 > 0:19:02The downside was a sluggish metabolism, just like sloths today.
0:19:08 > 0:19:14But the sloth's dung tells us a lot more than just what it ate.
0:19:14 > 0:19:19It's also a record of one species's struggle for survival
0:19:19 > 0:19:20during the Ice Age.
0:19:24 > 0:19:28So, all of this that looks like sediment is in fact excrement?
0:19:28 > 0:19:30This is all dung, this is all dry preserved dung
0:19:30 > 0:19:33and what you're seeing is the surface here,
0:19:33 > 0:19:36it's probably dating on the neighbourhood of 20,000
0:19:36 > 0:19:40and you're seeing going back through time down into different layers,
0:19:40 > 0:19:42further and further.
0:19:42 > 0:19:44We've obviously got some other animals here
0:19:44 > 0:19:47as well as ground sloths, there are tiny little pellets here, too.
0:19:47 > 0:19:48So what are those?
0:19:48 > 0:19:51These little pellets would be pack rats, little rodents.
0:19:51 > 0:19:55They're also scurrying around in here. And yeah, we'll find a little bit of that.
0:19:55 > 0:19:56But most of this stuff,
0:19:56 > 0:20:01most of this material, that is still Shasta ground sloth dung?
0:20:01 > 0:20:0499% is Shasta ground sloth right here.
0:20:04 > 0:20:09You get this pungent smell, and curiously, it's like a wine.
0:20:09 > 0:20:11The sweeter it is, it's older.
0:20:11 > 0:20:16This is old. Just by the smell, it's old.
0:20:16 > 0:20:20Do you ever think you've seen or smelled too much dung?
0:20:20 > 0:20:21Never! This is wonderful.
0:20:23 > 0:20:27At the back of the cave, the dung really piles up.
0:20:27 > 0:20:30And it's here that the beginning and the end
0:20:30 > 0:20:34of the Shasta ground sloth's story is written.
0:20:34 > 0:20:37- So this is where we're starting to get deeper and deeper.- Oh, yeah!
0:20:37 > 0:20:40- More and more time.- It's really building up here.- Yeah.
0:20:40 > 0:20:42It's all through here.
0:20:42 > 0:20:45Now this is the profile I really want to show you.
0:20:45 > 0:20:47- This is incredibly deep at this point.- Yeah.
0:20:47 > 0:20:50What we have is a metre and a half
0:20:50 > 0:20:54of almost pure Shasta ground sloth dung.
0:20:55 > 0:20:58If we look at the bottom of the unit,
0:20:58 > 0:21:02so we're looking at about, oh, say 40,000 years ago,
0:21:02 > 0:21:04the sloth dung is kind of telling us
0:21:04 > 0:21:07this is a good time to be in the Grand Canyon.
0:21:07 > 0:21:10Then when we get to THIS point right in here,
0:21:10 > 0:21:16now we're at 23,000 years old and something is happening.
0:21:16 > 0:21:17Oh, so this has changed completely.
0:21:17 > 0:21:20Now we're down into what looks like these little pellets.
0:21:20 > 0:21:22Is this the pack rats again?
0:21:22 > 0:21:27Yeah, all pack rat midden and different plants.
0:21:27 > 0:21:30And then this is about 16,000 years old.
0:21:30 > 0:21:32These dates are really significant
0:21:32 > 0:21:35because this means we are looking at the peak of the last Ice Age and it
0:21:35 > 0:21:40seems that for some reason, ground sloths aren't here at that time.
0:21:40 > 0:21:44That's precisely it, something is going on during the full glacial.
0:21:51 > 0:21:55As the ice reached its maximum extent, ground sloths
0:21:55 > 0:21:57abandoned the Grand Canyon.
0:22:02 > 0:22:06It was too dry for their favourite plants.
0:22:06 > 0:22:10And the drop in temperature didn't help.
0:22:10 > 0:22:15Sloths, with their slow metabolism, would have struggled to keep warm.
0:22:21 > 0:22:27It's easy to imagine chaos as the Ice Age really began to bite,
0:22:27 > 0:22:31with those giant ice sheets descending over half the continent.
0:22:36 > 0:22:39But although the sloth suffered,
0:22:39 > 0:22:45other giants thrived during the Ice Age...
0:22:47 > 0:22:54..none more so than one that used to stalk the badlands of Arizona.
0:23:02 > 0:23:07Back in the Ice Age, not everywhere was cold and dry.
0:23:08 > 0:23:13Large swathes of Arizona were covered in swamp...
0:23:17 > 0:23:23..home to an Ice Age giant that is possibly the weirdest mammal ever.
0:23:29 > 0:23:34So weird that scientists can't even agree quite what it looked like.
0:23:41 > 0:23:44A team from Arizona's Museum of Natural History
0:23:44 > 0:23:50has just found an impressive new specimen.
0:23:50 > 0:23:53The surrounding soil has been dug away
0:23:53 > 0:23:57and the creature, encased in plaster, ready to be moved.
0:24:04 > 0:24:07Dave Gillette is obsessed with these animals.
0:24:15 > 0:24:17Dave, what are these creatures?
0:24:17 > 0:24:19These are animals called glyptodonts.
0:24:19 > 0:24:21They're known for their rigid shell.
0:24:21 > 0:24:25It's quite strange looking at it like this, all covered in plaster.
0:24:25 > 0:24:27How big is the specimen inside that?
0:24:27 > 0:24:31Oh, it occupies almost the entire contents, as far as we can tell.
0:24:31 > 0:24:34Right, so this is a large creature?
0:24:34 > 0:24:40Yes, and it's an upside-down shell so that it's belly up, so to speak.
0:24:42 > 0:24:46Strangely, most of the glyptodonts Dave has discovered
0:24:46 > 0:24:48have been found upside down.
0:24:50 > 0:24:54I can't wait to see what these creatures were like.
0:24:54 > 0:24:59But first, Dave must solve the puzzle of how to get this one
0:24:59 > 0:25:01out of the ground.
0:25:01 > 0:25:03This is all really exciting.
0:25:03 > 0:25:05We're going to more the A-frame out of the way
0:25:05 > 0:25:08and the glytptodont can start its journey.
0:25:08 > 0:25:10It's been here for two million years
0:25:10 > 0:25:13and it's just about to go on its travels.
0:25:18 > 0:25:22The only thing holding this two-ton lump of fossil
0:25:22 > 0:25:25and earth together is the fragile coat of plaster.
0:25:29 > 0:25:33Do you think that the weight is OK, just on these four-by-fours?
0:25:51 > 0:25:52All right.
0:25:55 > 0:25:56Whoo!
0:25:58 > 0:26:01- I feel like - oh, happy day!- Yeah.
0:26:03 > 0:26:05Goodbye, glyptodont!
0:26:05 > 0:26:07SHE LAUGHS
0:26:07 > 0:26:12This find will join the world's greatest collection of glyptodonts
0:26:12 > 0:26:13at the museum in Mesa.
0:26:29 > 0:26:33Dave pieces together these specimens to get a better
0:26:33 > 0:26:36picture of this bizarre creature.
0:26:38 > 0:26:41Ah, Dave, these are fantastic! Are they all from Arizona as well?
0:26:41 > 0:26:44These are all from same area where we just finished excavating.
0:26:47 > 0:26:49Is this a hand or a foot we're looking at here?
0:26:49 > 0:26:51These are probably digging feet.
0:26:51 > 0:26:56We think that glyptodonts had a very strong digging motion.
0:26:56 > 0:26:58That's wonderful. What's this - is this a tail?
0:26:58 > 0:26:59This is a tail.
0:26:59 > 0:27:04- Each vertebra was protected by bony plates all the way around.- Yeah.
0:27:04 > 0:27:06And in fact the tail could be a weapon.
0:27:06 > 0:27:07It's incredibly chunky, isn't it?
0:27:07 > 0:27:10It's amazing, yeah.
0:27:10 > 0:27:14And this is a vertebra. This is really odd. It's so peculiar,
0:27:14 > 0:27:18cos I'm seeing bits of anatomy that I kind of recognise
0:27:18 > 0:27:20but it all seems to be a bit twisted.
0:27:20 > 0:27:23It's all very strange-looking to me.
0:27:23 > 0:27:26But it's still a mammal, so you can still recognise it as a mammal,
0:27:26 > 0:27:28even if it is strange.
0:27:28 > 0:27:31A very weird mammal. A very weird mammal.
0:27:33 > 0:27:38So put all the bits together, and what have you got?
0:27:38 > 0:27:43A bony shell with a belly that was covered in soft fur.
0:27:44 > 0:27:50An armoured tail and formidable claws.
0:27:50 > 0:27:52Just one crucial bit missing.
0:27:54 > 0:27:57What would the face of this glyptodont have looked like?
0:27:57 > 0:28:00Well, the face would have been very cheeky, fat on the side.
0:28:02 > 0:28:06The trunk would have extended from the nasal bones
0:28:06 > 0:28:08and extended for a foot or more.
0:28:08 > 0:28:10It had a trunk?
0:28:10 > 0:28:12I think it had a trunk. There's a lot of debate about that but
0:28:12 > 0:28:16I don't see any other feeding mechanism for glyptodonts.
0:28:16 > 0:28:20And do you think the bony arrangement that we can see
0:28:20 > 0:28:23here looks like it would have supported a trunk as well?
0:28:23 > 0:28:24I think it does.
0:28:24 > 0:28:28I see muscle scars on the front of these descending processes.
0:28:28 > 0:28:29That's great. I mean,
0:28:29 > 0:28:32- those are muscles which - in us - make us smile.- That's right.
0:28:32 > 0:28:34But in the glyptodont, they're about moving its trunk around.
0:28:34 > 0:28:38Well, maybe they could smile a little, too! THEY LAUGH
0:28:38 > 0:28:44It's by far the oddest mammal I've ever seen.
0:28:44 > 0:28:48More like some sort of mythological creature,
0:28:48 > 0:28:51like an enormous armadillo with a trunk!
0:28:55 > 0:28:59Even its teeth are peculiar.
0:28:59 > 0:29:01Look at its jaw - that's wonderful!
0:29:01 > 0:29:06This is spectacular. This is the left jaw, and these are the teeth.
0:29:06 > 0:29:08You see, there are eight teeth -
0:29:08 > 0:29:11all cheek teeth, no canines and no incisors.
0:29:11 > 0:29:12Oh, right.
0:29:12 > 0:29:14Yeah, and each tooth has three lobes.
0:29:14 > 0:29:18You can see there are grooves on the teeth and the ridges.
0:29:18 > 0:29:20So what were they eating with these teeth?
0:29:20 > 0:29:23Well, they were eating soft vegetation
0:29:23 > 0:29:25around the streams and lakes.
0:29:25 > 0:29:28These strange Christmas-tree-shaped teeth
0:29:28 > 0:29:31were made to chew on aquatic plants.
0:29:35 > 0:29:40Dave has found another unusual creature alongside the glyptodont.
0:29:45 > 0:29:47The capybara...
0:29:49 > 0:29:51..a giant rodent that still lives
0:29:51 > 0:29:53in the tropical swamps of South America.
0:29:56 > 0:30:02And in the Ice Age, it shared the Arizonan swamp with glyptodonts.
0:30:06 > 0:30:08So could they swim?
0:30:08 > 0:30:11I'm sure they could swim. I'm sure they could swim
0:30:11 > 0:30:13with other glyptodonts and capybaras
0:30:13 > 0:30:16and other animals in the water.
0:30:16 > 0:30:19Unlike its furry neighbour,
0:30:19 > 0:30:23this glyptodont is a challenge for any predator.
0:30:29 > 0:30:33Slow-moving perhaps, but armoured like a tank.
0:30:37 > 0:30:40A stand-off between two males.
0:30:40 > 0:30:45Each one is a ton of muscle and solid bone.
0:30:54 > 0:30:56THEY SCREECH
0:31:05 > 0:31:08Vanquished, the loser struggles to right himself.
0:31:13 > 0:31:16If a glyptodont died in the water,
0:31:16 > 0:31:18its bloated body would turn belly-up
0:31:18 > 0:31:21and eventually sink down to the river bed...
0:31:24 > 0:31:28..which could explain why so many are found upside down.
0:31:40 > 0:31:43So what turned the deserts into swamp?
0:31:47 > 0:31:53The answer lies with the impact the Great Ice Age had on the world.
0:32:00 > 0:32:04Over the last two and a half million years,
0:32:04 > 0:32:08there has been not just one Ice Age, but around 20 of them.
0:32:17 > 0:32:21Fossils reveal that every time the ice sheet grew,
0:32:21 > 0:32:26the Arizonan marshes expanded and the number of glyptodonts rose.
0:32:29 > 0:32:33And when the ice shrank, their numbers fell.
0:32:46 > 0:32:54The ice sheet was acting like a vast mountain range, two miles high,
0:32:54 > 0:33:01big enough to divert moisture-laden Pacific winds, pushing them south...
0:33:02 > 0:33:04THUNDERCLAPS
0:33:11 > 0:33:17..watering the desert and turning it into a lush wetland paradise.
0:33:21 > 0:33:23Across the continent,
0:33:23 > 0:33:30the Ice Age created new worlds for other giants to exploit.
0:33:30 > 0:33:36And there's one animal in particular that benefited.
0:33:36 > 0:33:39The greatest giant of them all.
0:33:44 > 0:33:48Hidden in the sea mist, on a coastal plain just
0:33:48 > 0:33:52north of San Francisco, some large rocks stand tall...
0:33:58 > 0:34:01..sentinels that still bear witness
0:34:01 > 0:34:04to the wanderings of an Ice Age leviathan.
0:34:09 > 0:34:14State archaeologist Breck Parkman has spent decades examining
0:34:14 > 0:34:17every square inch of these rocks.
0:34:21 > 0:34:23- Look at this.- It's polished.
0:34:23 > 0:34:26- It is polished.- What do you think caused it - is it weathering?
0:34:26 > 0:34:28No, actually, I think this is all from animals.
0:34:28 > 0:34:31Every bit of this is from animals.
0:34:34 > 0:34:39Large mammals often need a good scratch,
0:34:39 > 0:34:43perhaps to dislodge unwanted guests, like ticks.
0:34:46 > 0:34:50Breck believes that over a long period of time
0:34:50 > 0:34:53animals have polished these rocks to a shine.
0:34:59 > 0:35:01Have you tested this hypothesis?
0:35:01 > 0:35:05I have. We've worked in the lab, and we have taken samples
0:35:05 > 0:35:09of rocks that were known to be polished by wind and by water
0:35:09 > 0:35:11and by faulting and it doesn't compare.
0:35:11 > 0:35:15We've actually looked at something like three or four dozen
0:35:15 > 0:35:17other ideas, some of which are crazy, you know -
0:35:17 > 0:35:22what happens when kelp moves against the rocks, what happens with
0:35:22 > 0:35:24guano on the rocks, and what happens here -
0:35:24 > 0:35:26and you have to see it, though, and you're seeing it today -
0:35:26 > 0:35:28you have to see it to see the selectivity.
0:35:28 > 0:35:32Where is the polish and where isn't it? And it's these knobs and
0:35:32 > 0:35:37overhangs - it's up to a certain height and doesn't go higher.
0:35:37 > 0:35:41Some surfaces have been worn mirror-smooth.
0:35:45 > 0:35:48Oh, that's amazing. That's a massive area of polish.
0:35:54 > 0:35:58But there's one very revealing bit of polishing.
0:36:03 > 0:36:05Wait until you see this rock!
0:36:07 > 0:36:09So what have we got here?
0:36:09 > 0:36:10Well, we have more polish.
0:36:10 > 0:36:13But look at this. Look at how high this polish is.
0:36:13 > 0:36:16Oh, yeah! That's a bit too high for a sheep.
0:36:16 > 0:36:18And look at this. This is just the beginning.
0:36:18 > 0:36:22this polish goes right on up, right on up as high as I can reach.
0:36:22 > 0:36:24This is close to 14 feet here.
0:36:24 > 0:36:27Oh, so that's too high for a horse or a cow as well?
0:36:27 > 0:36:30You can have a horse sitting on the shoulder of a cow
0:36:30 > 0:36:32and still not do that.
0:36:32 > 0:36:35That's much too high for domestic livestock.
0:36:35 > 0:36:41So this is caused by an animal which no longer exists in North America. So what is it?
0:36:41 > 0:36:43I think it's mammoth.
0:36:43 > 0:36:48And 14 feet is actually the shoulder height of really large Columbian mammoth.
0:36:48 > 0:36:51- Oh, that's just fantastic! - Isn't it?
0:36:55 > 0:36:59A Columbian mammoth had the same characteristic shape
0:36:59 > 0:37:02as the woolly mammoth, with a domed head.
0:37:02 > 0:37:06But a Columbian was much larger and virtually bald.
0:37:12 > 0:37:18Its tusks were magnificent, much longer than an elephant's.
0:37:34 > 0:37:36The herd arrives at a favourite stop-over.
0:37:43 > 0:37:48A chance to exfoliate and scrape off some parasites.
0:37:53 > 0:38:00Amongst these rocks you can feel the presence of those Ice Age beasts.
0:38:00 > 0:38:04It's almost as though the ghosts of the mammoth are still with us.
0:38:07 > 0:38:13But where were these migrating Columbian mammoths actually going to?
0:38:13 > 0:38:17Surely they didn't come all this way just for a scratch?
0:38:21 > 0:38:25Once again, the Ice Age holds the answer.
0:38:25 > 0:38:31As more and more water froze, there was less to fill the oceans.
0:38:36 > 0:38:39At the height of the last Ice Age,
0:38:39 > 0:38:44the global sea level would have been 120 metres lower than it is today.
0:38:44 > 0:38:46So here on the coast of Northern California,
0:38:46 > 0:38:51the land would have extended out, almost to the horizon.
0:39:10 > 0:39:17The great bay of San Francisco became a vast, verdant valley.
0:39:22 > 0:39:27From the Golden Gate, the land stretched 26 miles out to sea.
0:39:32 > 0:39:37What is now a lonely coastal outcrop, back then,
0:39:37 > 0:39:41was a milestone in a lost land.
0:39:43 > 0:39:48The Columbian mammoths themselves contain clues as to what this place was like.
0:39:52 > 0:39:56Their teeth are like millstones,
0:39:56 > 0:40:00perfect for grinding up two tons of grass every week!
0:40:13 > 0:40:15This land was a vast prairie.
0:40:19 > 0:40:24Today, nearly all of the mammoth's coastal grassland
0:40:24 > 0:40:27lies beneath the waves.
0:40:27 > 0:40:30But there is one fragment left.
0:40:34 > 0:40:36This is Point Reyes
0:40:36 > 0:40:43and it is a tiny fragment of what was once a vast coastal prairie.
0:40:46 > 0:40:50This vegetation is perhaps the closest that we can get
0:40:50 > 0:40:53to what was out there on the coastal plains.
0:40:53 > 0:40:57This is bunch grass and it's incredibly tough stuff.
0:40:57 > 0:41:02It positively thrives on being grazed right down to the ground
0:41:02 > 0:41:04and then it sprouts back again.
0:41:04 > 0:41:08And amongst the grasses, we've got beautiful wild flowers.
0:41:08 > 0:41:11There are irises and buttercups amongst them.
0:41:11 > 0:41:15They look fantastic but they taste horrible.
0:41:15 > 0:41:20And that is an adaptation against being grazed.
0:41:20 > 0:41:24So what we've got here is a heavily grazed landscape.
0:41:24 > 0:41:28Today, the grazer is the cattle.
0:41:28 > 0:41:32Back in the Ice Age, it was the hungry mega-herbivores -
0:41:32 > 0:41:35the horse, the bison and the mammoth.
0:41:56 > 0:42:02Just one Ice Age grazer survives here - the tule elk.
0:42:13 > 0:42:17Such fleeting glimpses of the Ice Age might have been
0:42:17 > 0:42:24all we had, were it not for one truly amazing discovery...
0:42:26 > 0:42:31..one which means we can rebuild Ice Age America
0:42:31 > 0:42:36with all of its creatures - great and small!
0:42:40 > 0:42:43I need to return south.
0:43:02 > 0:43:05This is just so strange. There seems to be a road
0:43:05 > 0:43:09pouring down the side of this hill, and this is asphalt,
0:43:09 > 0:43:12but it's natural asphalt and at the top of it,
0:43:12 > 0:43:17I'm hoping to find some sticky tar coming up out of the ground.
0:43:23 > 0:43:25Now this looks a bit more like it.
0:43:25 > 0:43:27I don't really want to step down here because
0:43:27 > 0:43:31I suspect that this could be quite sticky, so
0:43:31 > 0:43:32let's prod it and see.
0:43:35 > 0:43:36Yeah, look at that.
0:43:36 > 0:43:40We've got some lovely, sticky tar coming up there.
0:43:42 > 0:43:47Natural asphalt or tar is very similar to heavy crude oil.
0:43:48 > 0:43:53In parts of California, it wells up through cracks in the earth.
0:43:59 > 0:44:02Deposits like this drove California's oil boom.
0:44:05 > 0:44:11But in 1913, workers at the Rancho La Brea drilling site discovered
0:44:11 > 0:44:15more than they bargained for - thousands of fossils.
0:44:15 > 0:44:19Extinct giants that had become trapped in the tar
0:44:19 > 0:44:20during the Ice Age.
0:44:23 > 0:44:27Rancho La Brea became the most sensational Ice Age fossil site
0:44:27 > 0:44:29in the world.
0:44:31 > 0:44:35And important new discoveries are still being made.
0:44:42 > 0:44:47In the vaults, there are over three million specimens,
0:44:47 > 0:44:51representing more than 600 different species -
0:44:51 > 0:44:55including the star of the show.
0:44:55 > 0:44:59There are hundreds of sabre-tooth cats - Smilodons - in this collection.
0:44:59 > 0:45:03In fact, as we walk down this corridor, everything
0:45:03 > 0:45:05down here on my left and my right -
0:45:05 > 0:45:09it's all Smilodon as far as the eye can see.
0:45:09 > 0:45:13Smilodon, Smilodon, Smilodon,
0:45:13 > 0:45:16all the way to the end of this corridor.
0:45:16 > 0:45:21And then we turn around and we're into herbivore alley.
0:45:21 > 0:45:28We start with two species of bovid. This is Bison antiquus
0:45:28 > 0:45:34and then on the right here, we are into equus - horses.
0:45:34 > 0:45:37We have two species of horse at La Brea.
0:45:37 > 0:45:41Here is the Western Horse.
0:45:41 > 0:45:46And these are its toe-bones which bore the hooves.
0:45:46 > 0:45:52And then we have three species of sloth.
0:45:52 > 0:45:55And these are perhaps my favourite species of animal actually at La Brea
0:45:55 > 0:45:58after the sabre-tooth cats.
0:45:58 > 0:46:03And right towards the end of this corridor we are going to find
0:46:03 > 0:46:10Paramylodon, or Harlan's ground sloth. Here it is.
0:46:10 > 0:46:14And these are its finger bones. Just imagine the claws that
0:46:14 > 0:46:18then extended from them, quite formidable.
0:46:18 > 0:46:21And we've got two species of the camel family.
0:46:21 > 0:46:28Over here, these are the neck vertebrae of Yesterday's Camel.
0:46:28 > 0:46:33And that's quite impressive but we haven't got onto the four species of mustelid -
0:46:33 > 0:46:37that's weasels and badgers, and the three species of rabbit,
0:46:37 > 0:46:40the two species of deer, two species of antelope,
0:46:40 > 0:46:44two species of elephant, one of tapir and one of peccaries.
0:46:44 > 0:46:47And that's not even counting the small mammals.
0:46:53 > 0:46:58Each creature is helping to populate that empty Ice Age landscape.
0:47:11 > 0:47:13And the tar keeps on revealing
0:47:13 > 0:47:17more about the land of the sabre-tooth cat.
0:47:20 > 0:47:23A few years ago, the Museum of Art over there next to the tar pits
0:47:23 > 0:47:26decided it wanted an underground car park,
0:47:26 > 0:47:29but there are tar pits over there as well.
0:47:29 > 0:47:31So the palaeontologists were called in,
0:47:31 > 0:47:34and rather than rush through an excavation there and then,
0:47:34 > 0:47:37they took the sediment out en bloc,
0:47:37 > 0:47:40and brought it back over here in these massive wooden crates
0:47:40 > 0:47:43and now they're carefully excavating each one of them.
0:47:57 > 0:48:02The place feels more like a trailer park than a palaeontological dig!
0:48:10 > 0:48:13'Each box is excavated, grain by grain,
0:48:13 > 0:48:16'by its own resident palaeontologist.'
0:48:21 > 0:48:25- Laura.- Oh, hi.- Hello.- Hi.
0:48:26 > 0:48:28Welcome to box one!
0:48:28 > 0:48:33Laura has been here for nearly a year.
0:48:34 > 0:48:37What are you actually excavating here? It's a real mass of bones.
0:48:37 > 0:48:38It really, really is.
0:48:38 > 0:48:41It's just a kind of a tangled mess at this point.
0:48:41 > 0:48:44Um, but I've got baby bison, maxilla, so, front of his face.
0:48:44 > 0:48:47This one here, you can see his teeth down there.
0:48:47 > 0:48:51- And from more teeth, I got dire wolf, lower jaw.- Yeah.
0:48:51 > 0:48:55'So far, she's got through two metres of bone deposits.'
0:48:55 > 0:48:56It's painstaking work.
0:48:56 > 0:49:00- But it's fun! I get to dig for buried treasure for my job.- Yeah!
0:49:00 > 0:49:01This whole project, Project 23 -
0:49:01 > 0:49:05what's the most exciting thing that's emerged from it so far, do you think?
0:49:05 > 0:49:08One of my favourite things anyway is from box 1.
0:49:08 > 0:49:12We have...we kind of nicknamed our own entire family of sabre-tooth cats.
0:49:12 > 0:49:15So far, just from this one deposit right here,
0:49:15 > 0:49:19we have at least three adults, three sub-adults - teenagers,
0:49:19 > 0:49:22and four separate sabre-tooth kittens.
0:49:22 > 0:49:25- Kittens?- Like you can see right here.- Sabre-tooth kittens!- I know!
0:49:25 > 0:49:27Let's see, I have sabre-tooth kitten.
0:49:27 > 0:49:29Ulna. So that's one of the forearm bones.
0:49:29 > 0:49:32We've got more sabre-tooth kitten, we have a thoracic vertebrae.
0:49:32 > 0:49:34Middle of his back.
0:49:34 > 0:49:38And let's see, just over here, that's half from the pelvis.
0:49:38 > 0:49:40This one's from an adult sabre-tooth cat.
0:49:40 > 0:49:43In fact, there's this one day that I actually found three separate
0:49:43 > 0:49:45sabre-tooth kitten sabres all in one day.
0:49:45 > 0:49:48I must admit, that's probably one of my favourite days here.
0:49:53 > 0:49:56The kittens' remains are being scrutinized
0:49:56 > 0:49:59by La Brea sabre-tooth cat expert Chris Shaw.
0:50:04 > 0:50:07These are the most recent sabre-tooth cat bones
0:50:07 > 0:50:11that we have gotten from their project here.
0:50:11 > 0:50:13And these kittens are fantastic.
0:50:13 > 0:50:15We've got their little milk teeth, sabres.
0:50:15 > 0:50:19- Those are the milk teeth.- Can I pick that one up?- Yes, you may.
0:50:19 > 0:50:21- Thank you. - These are the real thing.- Wow!
0:50:21 > 0:50:25And you'll notice, too - if you rub your finger along the edge
0:50:25 > 0:50:30- of that, it's actually serrated and very sharp.- Ooh!
0:50:30 > 0:50:32- That's like a knife blade.- Exactly.
0:50:32 > 0:50:36These animals could puncture skin much like the adults.
0:50:36 > 0:50:39You can feel those...I can barely see those serrations,
0:50:39 > 0:50:41they're really tiny, aren't they?
0:50:41 > 0:50:44- But I can certainly feel them, rubbing my finger along it.- Yes.
0:50:44 > 0:50:46And these teeth grow in,
0:50:46 > 0:50:50and were actually erupted at the time of birth.
0:50:52 > 0:50:56It's unlikely that the kittens used their sabre teeth to kill.
0:51:06 > 0:51:09Their serrated teeth were like steak knives,
0:51:09 > 0:51:13ideal for scavenging after Mum had made the kill.
0:51:16 > 0:51:20The sheer number of specimens here gives scientists
0:51:20 > 0:51:23the chance to understand not only the anatomy,
0:51:23 > 0:51:26but the behaviour of these extinct cats.
0:51:29 > 0:51:31And one find, in particular,
0:51:31 > 0:51:35is transforming our understanding of how sabre-tooth cats behaved.
0:51:37 > 0:51:40It's a disfigured pelvis,
0:51:40 > 0:51:46one that shows signs of a condition that I've seen before - in humans.
0:51:46 > 0:51:49This is one of my favourite specimens.
0:51:49 > 0:51:52What you have is a very, very nasty injury, and a massive,
0:51:52 > 0:51:54massive infection.
0:51:54 > 0:51:55This...I was going to say,
0:51:55 > 0:51:58this looks to me like septic arthritis.
0:51:58 > 0:52:03This looks like the type of bone growth that you get around a joint which has become infected.
0:52:03 > 0:52:07It's exactly that. And the femur itself, the thigh bone, is really,
0:52:07 > 0:52:08really worn down.
0:52:08 > 0:52:11That's just quite shocking. I mean, this would have been an animal
0:52:11 > 0:52:12- which was limping.- Right, exactly.
0:52:12 > 0:52:15This animal wouldn't have been able to run after prey,
0:52:15 > 0:52:17and yet we can say, looking at this,
0:52:17 > 0:52:20- this has been a long-standing condition.- Absolutely.
0:52:20 > 0:52:24For all of this bone to have grown to this extent,
0:52:24 > 0:52:26this animal has survived for months
0:52:26 > 0:52:29and possibly even years with this going on.
0:52:29 > 0:52:33That's absolutely correct and that's the premise of my idea,
0:52:33 > 0:52:36that these animals were in fact social animals.
0:52:36 > 0:52:42That would enable this animal to survive because the rest of the group would bring in the food
0:52:42 > 0:52:48and nurture this animal by letting it feed at kills.
0:52:52 > 0:52:57So not only did this giant cat possess daggers for teeth,
0:52:57 > 0:53:01it's likely that it hunted in groups, much like lions today.
0:53:07 > 0:53:11Sabre-tooth cats must have been utterly terrifying.
0:53:16 > 0:53:19A herd of Columbian mammoths
0:53:19 > 0:53:23is making its annual migration from the coast.
0:53:23 > 0:53:27A young male wanders away from the herd...
0:53:30 > 0:53:36..straight into the path of a pack of sabre-tooth cats.
0:54:19 > 0:54:22But the tar makes it impossible for them to escape.
0:54:24 > 0:54:27This is their last meal.
0:54:37 > 0:54:43The tar has preserved dramatic stories of Ice Age giants.
0:54:43 > 0:54:47But it also holds clues to the world they lived in.
0:54:51 > 0:54:55Hidden amongst the giant bones are much smaller ones.
0:55:02 > 0:55:07And it's these microfossils that can tell us just why this place
0:55:07 > 0:55:12was such a happy hunting ground for sabre-tooth cats.
0:55:17 > 0:55:22Tiny animals like snails and beetles are very sensitive to climate.
0:55:26 > 0:55:30So these species are the best indicators of what the lost
0:55:30 > 0:55:34Ice Age environment was really like.
0:55:34 > 0:55:38What we find is that this area of Southern California was in fact
0:55:38 > 0:55:42cooler and wetter and more lush.
0:55:46 > 0:55:50A beautiful, temperate parkland of open areas
0:55:50 > 0:55:55and woods, populated by these magnificent animals.
0:56:23 > 0:56:26For America, the Ice Age
0:56:26 > 0:56:30was actually the golden age of megafauna.
0:56:43 > 0:56:47But meanwhile, in the rest of the northern hemisphere,
0:56:47 > 0:56:51the ice sheets were going to have a very different impact.
0:56:56 > 0:57:01The most bitter struggle that the Ice Age animals would face was
0:57:01 > 0:57:06not in North America but here, on the other side of the Atlantic
0:57:06 > 0:57:10in the mountains and plains of Europe and Siberia.
0:57:15 > 0:57:19Here, the Ice Age hit with brutal force.
0:57:22 > 0:57:26Next time, I witness the struggle to survive.
0:57:28 > 0:57:31Deep within a cave in Transylvania,
0:57:31 > 0:57:36grisly remains tell of a spectacular fight to the death.
0:57:36 > 0:57:38THEY ROAR FEROCIOUSLY
0:57:40 > 0:57:44And the woolly mammoth faces its own battle for survival
0:57:44 > 0:57:46against a new and cunning predator.
0:58:12 > 0:58:15Subtitles by Red Bee Media Ltd