- [Announcer] They thrilled us.

They surprised us.

They took us somewhere we've never been before.

The awe-inspiring six-part adventure "Walking with Dinosaurs" brought prehistoric life roaring back with stunning visuals and real science.

(gentle orchestral music) (ocean waves) - [Narrator] Over 66 million years ago, (dinosaur screeching) our world... (dinosaurs calling) was ruled... (dinosaurs chattering) by dinosaurs.

(dramatic percussion music) - [Announcer] In this special look at the hit series, we are revisiting the most unforgettable moments, breathtaking creatures and epic stories that brought the lost world to life.

We'll spend time with Clover the Triceratops, Sobek the Spinosaurus, George the Gastonia, Rose the Albertosaurus, Albie the Pachyrhinosaurus, and who could forget the love story between two Lusotitans?

(lighthearted orchestral and percussion music) We'll travel around the world to spend time with leading paleontologists in the field as they unearth dinosaur bones and unlock some of the mysteries from this era.

- [Nikki] Check out these teeth.

(dramatic orchestral music) - [Announcer] We'll go behind the scenes with the filmmakers to learn a little bit about how they brought these giants to life.

So please fasten your seatbelt and get ready for a wild ride filled with excitement.

And of course, there will be lots of nail-biting suspense as we experience "Walking With Dinosaurs: A Viewer's Guide" (dramatic music crescendoing) In Episode One, we are introduced to Clover, a young Triceratops who will encounter some of the most famous species of dinosaurs to ever walk the earth.

(intriguing orchestral music) - [Narrator] Eastern Montana-- a vast, untamed wilderness... (horse snorting) (hooves scattering stones) with extraordinary stories to tell.

(intriguing music continuing) Here, a team from the North Carolina Museum of Natural Sciences (archaeology tools clinking) is excavating an iconic species, (intriguing music continuing) a Triceratops.

(intriguing music continuing) But this is no ancient giant.

(intriguing music continuing) - [Eric] But it's really small-- very young individual.

(intriguing music continuing) - [Narrator] The team calls her Clover.

(tool dragging through sand) Studying her bones... we can begin to imagine her world (chisels tapping) and tell her story... for the first time.

(tapping and scraping) Where Montana is today, (insects chirping) there is a lush landscape of sprawling subtropical forests (waterfall rushing) crisscrossed by waterways.

(waterfall rushing) (dinosaur calling) This... is Laramidia, (awe-inspiring orchestral music) home... to prehistoric giants (heavy footsteps) and the occasional not-so-giant.

(hooves scuffling) (playful string music) (Clover trilling softly) Meet Clover the Triceratops.

Less than two feet tall... she's tiny!

Despite her size, Clover roams the jungle alone.

(water rushing over stones) (playful music continuing) (egg clattering) But curiosity... can be a dangerous thing... (foreboding orchestral music) (dinosaur snarling) when you are living in a land of monsters.

(foreboding music intensifying) (dinosaur landing) (tense percussion music) (pterosaur shrieking) - [Announcer] An Infernodrakon, a giant pterosaur from the end of the Cretaceous, with a 16-foot wingspan and a razor sharp beak.

(Infernodrakon snorting) (dramatic orchestral music) - [Narrator] But Clover is nimble, (Infernodrakon shrieking) (Clover crying) (soft nature sounds) (Infernodrakon chirping calmly) and this mother... just wants her egg back.

(Infernodrakon clucking) (poignant piano music) A mile from Clover's dig site... (hammer tapping) more fossilized remains are emerging.

(hammer tapping) - [Eric] It's a really thick tooth designed for crushing bones.

- [Narrator] It's a tooth that can only belong... (dramatic string music) to one animal.

(foreboding percussion music) - [Announcer] Tyrannosaurus Rex, Earth's most infamous apex predator.

With five-feet-long jaws, he stood at almost 13 feet tall and weighed almost nine tons.

(foreboding music continuing) - [Narrator] For Clover, a terrifying first encounter.

It's obvious from the evidence on the ground-- - [Eric] ...a bit of bone here coming out.

- [Narrator] That Clover's world was teeming with other dinosaurs.... (upbeat percussion music) - [Announcer] Triceratops had four-foot-long horns with bony shields over six feet wide.

These defenses made them one of the most successful dinosaur species of their time.

(upbeat music continuing) - [Narrator] ...meaning an adult Triceratops would be the perfect protector for Clover.

(Clover snuffling) But there's a problem.

(adult snorting) (ominous orchestral music) Who needs a troublesome youngster following you around?

(ominous music continuing) As dawn breaks, Eric and Nikki head into the badlands to see this enormous fossil.

(footsteps) (anxious orchestral music) It's the lower leg bone of a truly colossal dinosaur.

(anxious music continuing) Echoing through towering trees... (dinosaurs calling) the calls of perhaps the strangest dinosaurs who roam here.

- [Announcer] The Edmontosaurus was known as the cow of the Cretaceous.

These herd animals were plant eaters and weighed over six tons.

(upbeat string music) - [Narrator] These social creatures tolerate Clover, (upbeat music continuing) (Edmontosaurus grunting) and it's not just safety they offer.

(baby Edmontosaurus calling) A playmate.

(baby Edmontosaurus calling) (upbeat music continuing) (both making affectionate noises) But danger... is never far away.

(tense orchestral music) (Clover crying) With nowhere to hide, (ominous footsteps) it's a good time... to bump into an old acquaintance.

(tense music continuing) (dinosaurs growling) (T-Rex roaring) Few creatures can challenge T-Rex, (T-Rex grunting) but a full grown Triceratops might be the only animal that doesn't need to turn and run.

(foreboding percussion music) (Triceratops growling) Flushing blood into his frill creates huge, colorful eyespots.

(dinosaurs grunting) (Triceratops growling) They make Triceratops seem even bigger.

(T-Rex roaring) (Triceratops charging) (T-Rex screeching) But for T-Rex, there's still an easier meal close by.

(T-Rex snorting) (T-Rex snarling) For Clover, it seems as if time has run out.

But she still has one advantage-- (ominous orchestral music) -- her size.

(T-Rex roaring) (thrilling orchestral music) With T-Rex distracted, (dinosaurs scuffling) (thrilling music continuing) a moment... of surprise.

(Triceratops growling) (flesh tearing) (T-Rex groaning) (thrilling music ending gravely) Clover has survived her encounter with history's most infamous killer.

(music concluding and fading) For now... she's safe.

(Clover chirping) And while this old bull may not seek the company of a youngster, Clover's not giving up... just yet.

(gentle string music) (adult grumbling softly) - [Announcer] Now, let's hear from the paleontologist who discovered a new species of dinosaur, the Utahraptor.

- [Narrator] Utahraptor is the largest species of Raptor that ever lived.

(Utahraptor hissing) But until relatively recently... (pounding percussion music) no one knew this fearsome predator even existed.

In the early 1990s, paleontologist Jim Kirkland was working in the Utah Desert (gentle piano music) (lock clicking) when his team discovered a huge claw belonging to an unknown dinosaur.

(gentle music continuing) - [Jim] Well, when I first saw this claw, you know, I got real excited.

"We need to find more of this animal... This is something new, and it is huge."

(gentle string and piano music continuing) - [Narrator] Then in 2005, he got the lucky break he needed.

(gentle string and piano music continuing) - [Jim] A geology student reported some dinosaur bones coming out of the, uh, base of a cliff.

(intriguing orchestral music) (wood scraping) - [Narrator] So many bones so close together meant the team had to take them all out in one huge slab.

(slab dragging) - [Jim] We ended up having a nine-ton block filled with skeletons.

(intriguing music continuing) - [Narrator] After nearly a decade of excavation, they finally got it back to the lab-- - [Jim] Lift... and fold.

- [Narrator] And could begin to uncover what was inside.

(intriguing music continuing) - [Jim] There's more therapod material than anything I've ever seen.

Yeah, this thing, you know, is at least 95% meat-eating dinosaur bones.

Okay... (instrument scraping) - [Narrator] But deeper into the rock, the team began to find much larger bones.

- [Jim] We pulled a big tibia out of there with the ankle in place.

- [Narrator] Jim had finally found the dinosaur his mysterious claw belonged to.

(foot pounding) (dinosaur exhaling) But with most raptors the size of a turkey, how did Utahraptor get so big?

Jim thinks the answer could be linked to a little-known extinction event at the end of the Jurassic.

(footsteps crunching) - [Jim] We're putting together a new story that shows a major extinction in Earth history that hadn't really been recognized before.

We lose three major groups of large predatory dinosaurs, the kings of their creation.

They all go extinct.

- [Narrator] But the extinction of one species creates opportunities for the survivors.

With all the large predators gone, there was a gap at the top of the food chain.

(quiet piano music) And over millions of years, Utahraptor evolved to take over.

(quiet music continuing) - [Jim] There's this niche open.

You know, when no one is filling it, these things just got real big to take advantage of the hole in the landscape.

- [Narrator] A fortuitous find in the desert (footsteps crunching) (suspenseful string music) and an evolutionary lucky break gave us the largest raptor that's ever lived.

(footsteps crunching) (suspenseful music continuing) - [Announcer] In episode two, we meet Sobek, a Spinosaurus father who tries to provide for his babies.

(ethereal orchestral music) - [Narrator] Three-and-a-half million square miles of parched sand.

(wind blowing) The Sahara Desert... is one of the most inhospitable environments... on Earth.

(ethereal music continuing) Nizar and his team are excavating the remains of one of the largest predatory dinosaurs that ever lived-- a Spinosaurus.

Using the team's discoveries, we can imagine how it lived and died 100 million years ago.

(pensive string music) In the Late Cretaceous period... Africa has just broken away from South America... (pensive music continuing) and the land that will become the Sahara is a river system.

(pensive music continuing) (wind blowing) This is Sobek-- (Sobek grunting) the Spinosaurus.

(Sobek grunting) (bright woodwind music) - [Announcer] Sobek the Spinosaurus was 36 feet long and had a 20-foot tail.

His powerful jaws were packed with teeth.

(dinosaurs chattering) - [Narrator] Sobek... is a new dad.

(dinosaurs chattering) Sobek must keep his young family alive (dinosaurs chattering) until they can fend for themselves.

(dinosaurs chattering) - [Nizar] What I think is really remarkable is like you get close to the tip of the tail, and you still have these really long spines.

The more we collect, the more aquatic this thing becomes.

- [Emily] Yeah!

- [Narrator] For Nizar, a thin, flat tail can mean only one thing... (water bubbling) Spinosaurus was a swimmer.

(uplifting orchestral music) (dinosaur diving underwater) (water whooshing) (uplifting music continuing) Underwater, Sobek is in his element, (uplifting music continuing) using his huge tail to power him through the water.

(uplifting music continuing) (dinosaurs grunting) And with Dad's back turned... (water bubbling) this secluded backwater is the perfect kiddie pool.

(tranquil string music) (water bubbling) Hidden from view... (water bubbling) the murky waters are patrolled by at least eight species (ominous string music) of ferocious crocodile.

(dinosaur squawking) But that's the least of their worries... (leaves rustling) because the family has just entered the territory (heavy footsteps) (dinosaur exhaling) of Carcharodontosaurus.

(heavy footsteps) (foreboding orchestral music) - [Announcer] Carcharodontosaurus, the T-Rex of Africa.

These dinosaurs stood at 10 feet tall and were armed with more than 50 flesh-cutting teeth.

(footsteps) (dinosaurs roaring) - [Narrator] Time to get the babies to safety.

(footsteps) And not far from the dig site, the team has discovered signs of another monster.

(dramatic orchestral music) (dinosaur grunting) - [Announcer] Titanosaurs encompassed a wide variety of long-necked plant-eating dinosaurs.

Some species of Titanosaurs could stand at 65 feet tall and weigh up to 60 tons, as much as a herd of elephants.

(poignant orchestral music) - [Narrator] But for one elderly member of the group, (poignant music continuing) this has become its final resting place.

(dinosaur moaning) And it could provide Sobek with the food he needs (Sobek growling) for his hungry babies.

(quick footsteps) (dinosaur growling) An adult Carcharodontosaurus (dinosaurs squeaking) has already laid claim to the carcass.

(dinosaur growling) (fire crackling) Discovered close to the dig site... (fire crackling) it's the remains of an extinct species of fish.

(upbeat percussion music) - [Narrator] Onchopristis, also known as Sawskates, were bottom dwellers.

They could grow up to 13 feet in length, and their long snouts were lined with barbs in order to stun their prey.

- [Narrator] Like rays do today, it's thought they gathered to breed in their thousands, providing an incredible feast.

(suspenseful orchestral music) (heavy footsteps) But in this predator-infested land, (music and footsteps continuing) danger can strike at any time.

(suspenseful music continuing) (Alanqa screeching) - [Announcer] The Alanqa was a Kem Kem pterosaur, a flying reptile with a 23-foot wingspan.

They adapted to eat shellfish and small animals on the ground.

(dark orchestral music) (dinosaur rumbling) - [Narrator] For Alanqa, a young Spinosaurus... would make a tasty meal.

(dinosaur grunting) (dinosaur screeching) Losing one of his babies is a huge blow.

(Sobek grumbling) As the family emerges from the forest, (Sobek grumbling) their journey's end is in sight.

(Sobek grumbling) The Sawskate breeding ground... (inspiring string music) (water bubbling) and the promise of plentiful food for Sobek and his family.

(inspiring music continuing) (tense orchestral music) (dinosaur growling) (music intensifying) (water bubbling) (violent splashing) Success!

(tense music concluding) But getting his catch to his family won't be easy.

(dinosaurs grumbling) (deliberate footsteps) (dinosaurs roaring) (Sobek screeching) (claw slashing) (dinosaur growling) (dinosaurs roaring) (ominous orchestral music) This time, Sobek is in no mood to give up his kill.

(footsteps) (dinosaurs cooing) (prey dropping) (smacking and crunching) By leading them to this land of plenty... (hopeful orchestral music) Sobek has ensured his babies' survival.

(dinosaurs chattering) But his moment of triumph... has come at a terrible cost.

(bittersweet orchestral music) In providing for his babies, he has paid the ultimate price.

(Sobek growling) (footsteps crunching) (Sobek moaning) (Sobek exhaling) (pensive piano and string music) And as the great river ebbs and flows, it covers his body with layer upon layer of sediment, preserving Sobek's story beneath the desert's shifting sands until he is eventually found... 100 million years later.

(piano and string music brightening) - [Announcer] When we return, the journey continues with new creatures, new dangers, and new discoveries from the next chapters of this amazing series.

We'll also go behind the scenes with the filmmakers to see how they bring these prehistoric giants back to life.

You won't want to miss any of these details in "Walking with Dinosaurs: A Viewer's Guide."

(inspiring orchestral music concluding) - [Announcer] Welcome back to "Walking With Dinosaurs: A Viewer's Guide."

We're reliving the most thrilling moments from the series, and giving you a closer look at the incredible cast of creatures that once ruled the Earth.

Coming up, we'll go behind the scenes in Portugal with the filmmakers to see how they bring these fascinating, prehistoric stories to life with such vivid detail.

(energetic orchestral music) But first, let's take a look at Episode Three, where George, a young Gastonia bands together with several other teenagers in order to fight against the deadly Utahraptors.

(orchestral music fading) (car engine) - [Narrator] Utah, in the heart of the American West, (intriguing orchestral music) paleontologists Jim Kirkland and Josh Lively have made a remarkable discovery-- (intriguing music continuing) the bones of one of the most heavily armored dinosaurs that ever lived-- a Gastonia.

Using their discoveries, we can imagine how this youngster lived and died, 130 million years ago.

(music becoming more dramatic) In the Early Cretaceous Period, the land that will become Utah.. was warmer and wetter, covered by conifer forests, (music brightening) plentiful food for groups of plant-eating Gastonia, including youngster... George.

(George vocalizing) - [Announcer] Gastonia were herd animals.

Each Gastonia weighed over a ton and had thick, defensive armor.

(Gastonia chattering) Osteoderms were the bones that made up the Gastonia armor, and each osteoderm was covered by a thick scale.

(Gastonia chattering) - [Narrator] He must stick close to his parents because danger... is never far away.

(foreboding orchestral music) - [Announcer] Utahraptors were cousins of Velociraptors, about the size of a grizzly bear.

(Utahraptor vocalizing softly) - [Narrator] The ferns providing ideal cover... (Utahraptors vocalizing) for a surprise attack.

(music intensifying) (Gastonia bellowing) (Utahraptors hissing) (Gastonia grunting) (Gastonia bellowing) Like many modern herd animals, the adults form a defensive ring around their young, (Utahraptor hissing) (music intensifying) (Utahraptor thudding) (Utahraptors chattering) (Gastonia grunting) But George can't rely on the safety of the herd for much longer.

(dramatic percussion music) He's reaching adolescence, when, like all young male Gastonia, (George grunting) it's thought he'll be pushed out of the group.

(George grunting) (water rushing) but it's not long before he comes face to face with another young male.

(footsteps) (Gastonia grunting) (footsteps) (heads banging) (Gastonia growling) But this isn't a fight.

(Gastonia grunting) This is how Gastonia make friends.

(Gastonia grunting) Of all the armored dinosaurs... (Gastonia vocalizing) they're one of the only known social species.

George has just joined a group.

(Gastonia grunting) (soft footsteps) This gang of teenage boys will stay together until they're tough enough to fend for themselves.

(energetic orchestral music) - [Announcer] Utahraptors were finely tuned killing machines with eyesight as sharp as modern birds of prey.

They were 16 feet in length and had foot-long blades on their feet.

(energetic music concluding) (Gastonia grumbling) - [Narrator] So when they hear the raptors coming, (Utahraptors screeching) the Gastonia freeze.

- [Jim] The Utahraptor liked to stalk in the brush, and the prey has no clue they're there, till they went in striking distance.

And as soon as they did it, it would flex open its arms, you know, and leap, screaming at its prey.

It would happen so quick!

When you look at a lion attack or a leopard attack... (Gastonia roaring) Bam, you're on it.

(Utahraptor screeching) (Gastonia moaning) (dramatic orchestral music) (Utahraptor screeching) (Gastonia moaning) (George vocalizing and snorting) - [Narrator] Trapped at the water's edge... (Utahraptor grumbling) it looks like George's luck has run out.

(Gorge groaning) But at the dig, Josh and the team have made a discovery.

(hopeful string music) - [Announcer] Planicoxa were beaked, stocky dinosaurs that lived in herds and were most likely plant eaters.

(dramatic music continuing) (George groaning) - [Narrator] As the group leader closes in on George, (Utahraptor vocalizing) a herd of planet Planicoxa pass close by... (dramatic music intensifying) and without any armor, (dinosaurs chattering) they're a much easier kill-- (dinosaurs vocalizing) handing George... (Utahraptors shrieking) a very lucky escape.

The raptors are starving, but now, nearly fully grown, the Gastonia gang will stand and fight.

(Gastonia grunting) (dramatic music continuing) (Utahraptor screeching) (Gastonia roaring) (Utahraptor moaning) (Utahraptor thudding) But George's moment of triumph will be short-lived.

(anxious string music) The long, dry summer months have created a time bomb.

(anxious music intensifying) (fire crackling and booming) As wildfire rages through the parched forest, (fire crackling and booming) (Gastonia grunting) it threatens the Gastonia (fire crackling) and the surviving raptors... (Utahraptor screeching) the flames driving the two mortal enemies together.

(Utahraptor calling) Panicked, the raptors run into trouble.

(footsteps splashing) (Utahraptors screeching) (music pounding) (Utahraptors groaning) With the raptors out of the way, George has the chance to escape, (fire crackling) (George bellowing) but they're struggling.

(Gastonia moaning) The very things that protected them from the raptors-- heavy armor, and short stocky legs-- mean George and the gang are too slow... to escape the fire.

One by one... (Gastonia breathing heavily) the smoke takes its toll.

The landscape is transformed around them, (plaintive string music) until George and the gang are finally found 130 million years later.

(plaintive music concluding) - [Announcer] Now, let's take a behind-the-scenes look at how the show's creators bring these dinosaurs to life.

(reflective string music) - [Narrator] Spinosaurus is one of the largest meat-eating dinosaurs ever discovered.

(Spinosaurus grunting) Bringing such a weird dinosaur to life is a major challenge for the "Walking with Dinosaurs" Team.

(contemplative orchestral music) - [Neil] And then what we can do, Steve-- you know the shot that we did on the... slider yesterday?

- [Stephen] Yeah.

- [Narrator] And it starts with filming the environment it inhabited.

(orchestral music continuing) This unique part of southeast Portugal is one of the best matches for the river delta Spinosaurus called home.

(orchestral music continuing) - [Stephen] So, we're here down by this... uh, river, to film a sequence in the film where the Spinosaurs gather to fish.

(foreboding orchestral music) - [Narrator] But today, the weather isn't being kind.

(crew murmuring) (plastic fluttering) - [Stephen] Yeah, I think it's gonna be a bit in and out today, but, um, hopefully, we'll get some sun later on.

Hopefully!

(chuckling) (foreboding music concluding) (waves lapping shore) - [Narrator] Luckily for the crew, the rain soon clears.

(inspiring orchestral music) To help imagine the dinosaur action, they use scale cutouts as stand-ins for the digital models.

- [Stephen] It's a challenge filming things that aren't there but to try and help us visualize the size and the scale, we've got people with poles, and we've got some tape measures so that we make sure that we actually get the dinosaurs in the frame, and they're always sort of a lot bigger than you imagined.

(dramatic orchestral music) - [Narrator] With the stand-ins in place, the team positioned the camera to capture the action.

- [Neil] ...and two, Steve.

- [Steve] And... action!

(serene orchestral music) - [Neil] I don't think there's any way that we would be walking around this close to these creatures, but actually, for this moment, it just feels like the best way to approach it.

You really wanna get the camera in there and up close, and really feel like you're, you're part of it.

(tape measure clicking and extending) - [Narrator] Once the real-world environments are captured, it's time for Spinosaurus to walk in them-- (inspiring orchestral music) (footsteps) which is tough when you've been extinct for 94 million years.

(Spinosaurus roaring) So, it's over to the visual effects team.

- [Kirsty] We wanted to tell great stories, but equally important, if not more important, was making sure that we are scientifically accurate, and I cannot tell you the level of research that we went to in this series.

- [Narrator] Our hero, Sobek, is an entirely computer-generated character, every detail carefully researched and designed from the claws up.

- [Daniel] We know what it looks like.

What we need to then sell is how it interacts with the environment.

(nervous string music) - [Narrator] And water is particularly tricky to create in the digital world.

Back in the field, the team is experimenting with a very unusual piece of equipment... (cheerful orchestral music) a perfect scale replica of a Spinosaurus head.

It's the same color as a blue screen, so it can easily be replaced by the visual effects team.

(cheerful music continuing) After practice in the pool... (cheerful music continuing) pushing it through the lake creates the hard-to-make splashes and ripples in real time.

(water birds chattering) It gives the animators a huge advantage, letting them blend the Spinosaurus model seamlessly into the real environment, enabling this strange dinosaur to walk and swim again.

(contemplative string music) - [Announcer] In Episode Four, we are introduced to a young Albertosaurus named Rose, who is struggling to survive within her own herd.

(contemplative music continuing) - [Narrator] Western Canada.

(contemplative music continuing) On the banks of Red Deer River, paleontologists from the University of Alberta (tools banging and scraping) are unearthing the final resting place of a superpredator, Albertosaurus, T-Rex's deadly cousin.

The team calls her "Rose."

(tools clinking) Inspired by their discoveries, we can imagine her story.

(dramatic orchestral music) Laramidia, a land in crisis.

(dramatic music continuing) Atmospheric changes have forced temperatures down by two degrees Celsius.

(dramatic music continuing) Food is scarce... (dinosaurs calling and flapping) (dramatic music continuing) even... for an apex predator.

(membrane shifting) - [Announcer] Rose the Albertosaurus was eight feet tall, with the weight and power of a full grown rhinoceros.

They were able to sprint up to 30 miles an hour, meaning that at one time they were possibly the fastest land predator on the planet.

(inspiring orchestral music) (Rose growling) - [Narrator] This... is Rose.

It's been a week since she last ate, (inspiring music continuing) but in her sights-- an Arrhinoceratops.

(inspiring music continuing) - [Announcer] Arrhinoceratops were four-legged plant-eating dinosaurs weighing two tons.

(inspiring music continuing) (Arrhinoceratops growling) - [Narrator] But Rose has miscalculated.

Her target is twice her weight.

(Arrhinoceratops growling) Rose is starving, (dinosaurs roaring) but the risk of injury is just too great.

(somber orchestral music) Albertosaurus are social animals.

(soft footsteps) They live and hunt together, forming strong, intimate bonds.

(footsteps) (dinosaurs snuffling) Rose has paired with this male Albertosaurus the same age, (quiet vocalizing) and starvation isn't the only threat hanging over Rose.

(quiet vocalizing) The matriarch.

(Albertosauruses grumbling) And Rose is bottom of the pecking order.

(Albertosauruses growling) She'll have to prove herself when it matters most.

(Albertosauruses grumbling) They're venturing further up Red Deer River, (water splashing) on the hunt for more giants, (water rushing) and the first clue... - [Henry] We got a rib here.

- [Narrator] ...to what might have fed the Albertosaurus pack.

(upbeat orchestral music) - [Announcer] Edmontosaurus were plant-eating duck-billed dinosaurs.

(upbeat music continuing) (wildebeests grunting) - [Henry] If you think of wildebeests in, uh, Africa right now, that's Edmontosaurus, because they're everywhere here.

(wildebeests grunting) - [Narrator] Experts believe Edmontosaurus grouped together in herds.

(Edmontosaurus vocalizing) - [Henry] And so, living in groups means that you could have one or two animals kind of looking out while the rest feed.

(dramatic orchestral music) - [Narrator] At this time of year, this area should be teeming with Edmontosaurus, (dinosaurs snorting) but the herds are nowhere to be seen.

(dramatic music continuing) Rose spots an opportunity.

(distant roaring) - [Announcer] Cryodrakons were giant pterosaurs.

They were flying reptiles with a 20-foot wingspan.

(dramatic music intensifying) - [Narrator] Approaching from downwind, and with the pterosaurs' attention on their meal, (pterosaurs crunching) the youngsters close in.

(dramatic music pounding) (hissing and roaring) (jaws snapping) (pterosaur crying) (roaring) (body crunching) As a new day dawns, (reflective orchestral music) the pack's luck may be about to change.

(reflective music crescendoing) The Edmontosaurus have finally made it to their summer feeding ground.

Rose and her mate split off from the pack.

(dinosaurs vocalizing) (slow footsteps) As the swiftest runners, they must identify a target (dramatic orchestral music) and separate it from the herd.

Impulsive and inexperienced, (thrilling string music) (mate vocalizing) Rose's mate blindly charges into the herd.

(string music intensifying) (stampeding) (dinosaurs roaring) (string music intensifying) (stampeding) (dinosaur screeching) (Rose roaring) (stampeding) (Rose roaring) Rose has lost her closest companion.

(Rose exhaling) (tools scraping) The team estimates Rose's skull would have been about two feet long.

(intriguing orchestral music) Big, but not big enough to take down huge prey like Edmontosaurus.

(intriguing music continuing) But maybe she didn't have to.

(dinosaur roaring) Rose bides her time (dramatic percussion music) until she spots an older individual.

(Rose snorting) (dramatic music intensifying) Rose can't take this Edmontosaurus down alone, (dinosaurs growling) (footsteps quickening) but she can steer her prey (dramatic music continuing) (dinosaurs growling) right towards the killing jaws of the matriarch.

(drumbeats intensifying) (dinosaur roaring) (Rose growling) (dinosaur crying out) (Rose growling) (dinosaur moaning) (crunching and chewing) Rose has played her part to perfection.

(somber orchestral music) Finally, the pack can feed, (dinosaurs softly vocalizing) but these ancient lands hold one final surprise for the dino hunters.

(tools clinking) - [Mark] What do you got there, champ?

- [Christiana] What do you got?

- [Narrator] Colton has made a once-in-a-lifetime discovery.

- [Henry] Aw... what?

- [Mark] What is that?

- [Narrator] A tiny jawbone.

(workers chuckling) It's more evidence of the success of the Albertosaurus, (Rose vocalizing) and maybe the baby belonged to one of the pack females, (poignant orchestral music) perhaps even Rose herself.

(poignant music continuing) (Albertosaurus vocalizing) Rose, the young Albertosaurus, (Albertosaurus vocalizing) (Albertosaurus snorting) earned her rightful place (poignant music continuing) (Albertosaurus vocalizing) hunting... and surviving (poignant music intensifying) with her pack by her side.

(poignant music concluding) - [Announcer] When we return, the amazing journey to millions of years ago continues with new creatures, new dangers, and new discoveries from the next chapters of this incredible series.

You won't want to miss any of the excitement in "Walking with Dinosaurs: A Viewer's Guide."

(inspiring orchestral music concluding) (inspiring orchestral music) - [Announcer] Welcome back to "Walking With Dinosaurs: A Viewer's Guide."

In this final segment, we're reliving the most thrilling moments from the series.

And giving you a closer look at the prehistoric cast of creatures that once ruled the earth.

Coming up, we'll hear theories from modern paleontologists on what caused the extinction of these incredible animals.

But first, let's take a look at Episode Five, where we meet Albie, a toddler Pachyrhinosaurus.

(orchestral music fading) - [Narrator] Deep in the ancient forests of Alberta, Canada, discovered on the edge of a creek... (serene orchestral music) are the bones of a Pachyrhinosaurus.

Lying here is a toddler.... - [Paleontologist] It's such a tiny little bone.

- [Narrator] ...they call Albie.

By studying the bones, we can begin to tell their extraordinary story.

73 million years ago, what will one day be northwestern Canada, is part of a land mass called Laramidia.

Mountain ranges extend for thousands of miles.

This vast terrain is roamed by gigantic groups of plant-eating dinosaurs.

(insects buzzing) And by far the largest of these prehistoric herds... are the Pachyrhinosaurus.

- [Announcer] The Pachyrhinosaurus were close relatives of the Triceratops, and were social herd dinosaurs.

(upbeat string music) - [Narrator] The herd is setting out on an epic 400-mile trek north.

(dinosaurs plodding) It will be a grueling journey, especially if you're one of the youngest like Albie.

(Albie vocalizing softly) At less than a year old, he's under two feet tall, which makes keeping up a bit of a challenge.

(string music continuing) Following in their wake... an Azhdarchid pterosaur.

(intense string music) - [Announcer] Azhdarchid pterosaurs encompassed a wide variety of different species.

Some had 20-foot wingspans, and estimated speeds of 60 miles per hour.

(Pachyrhinosaurs grunting) - [Narrator] A close call.

(Pachyrhinosaurs vocalizing) Breeding season is upon them, (anxious orchestral music) so bulls in the herd must compete for their right to mate.

(anxious music intensifying) And there's only one way... to prove their worth.

(dinosaurs grunting) (rapid footsteps) (dramatic crash) (dinosaurs growling) - [Emily] Having good balance, uh, would be a better way to withstand individual-to- individual combat, which would be more common in a herd environment.

(heads smashing) - [Narrator] Each male seeks to deliver a bone-shattering blow.

(dinosaurs grunting) (dramatic music intensifying) (dinosaur roaring) (body thudding) The young rival... (dinosaur roaring) gains the upper hand.

(dinosaur moaning) In the chaos, Albie has become separated from his mother and lost in the crowd.

Finding her won't be easy.

(herd vocalizing) - [Emily] They have structures in their brains that are found in in herding animals today.

Things they probably would've used for individual identification.

- [Narrator] And the scan suggests parts of their brain were specialized to identify each individual's unique frill.

- [Emily] There's structures and they're closely associated with pattern recognition.

At a distance, they could see who was who.

(Albie grunting) - [Narrator] Finally... the distinctive outline of a frill (Albie vocalizing) he knows better than any other.

(Albie and mother grunting) (serene string music) Ancient footprints follow the herd's route.

This kind of speed and agility belongs to only one predator in the region, (dramatic percussion music) (footstep thudding) the Gorgosaurus.

(dinosaurs growling) - [Announcer] A Gorgosaurus was thought to have tracked their prey from up to 10 miles away.

They had exceptional hearing and a sense of smell more powerful than any other dinosaur.

(dramatic music fading) (stirring orchestral music) - [Narrator] This place would mark the end of the herd's long migration, (stirring music continuing) a haven where they could settle and begin to nest.

(stirring music continuing) (herd plodding and vocalizing) But while the exhausting 400-mile walk may finally be over, (dinosaurs grunting) (birds chirping) there is one problem they haven't left behind.

(distant roaring) (predator growling) The Gorgosaurus have stayed close.

(thrilling orchestral music) But their confrontation is about to pale into insignificance.

(music intensifying) (thunder rumbling) Both predator and prey face a far greater threat-- a devastating flash flood.

(rushing water) Water cascades into the valley, (dramatic orchestral music) swelling into an unstoppable torrent (waves crashing) that destroys everything in its path.

(thunder booming) The herd begins to panic, (dinosaurs roaring) mother and child... waiting by each other's side.

(thunder rumbling) (dinosaurs crying) But despite the devastation, this was perhaps not the end for them all.

(optimistic string music) Across the area, a series of fossils has been unearthed (optimistic music continuing) that point to an extraordinary possibility.

(optimistic music continuing) The young belonged to both Pachyrhinosaurus and Edmontosaurus-- (optimistic music continuing) dinosaurs that were heading for the same destination.

- Surviving animals could eventually have made their way here.

- [Narrator] Maybe, despite all the odds, (dinosaurs vocalizing) some of the herd did survive.

(inspiring orchestral music) (dinosaurs vocalizing) (leaves dropping) Survivors... (Pachyrhinosaurus roaring) with a chance to pave the way for the next generation to thrive.

(inspiring music continuing) So that one day, their herd can rise again.

(inspiring music continuing) (Pachyrhinosaurus roaring) (inspiring music concluding) - [Announcer] Now, let's hear the theories from modern paleontologists on what caused the extinction of these prehistoric giants.

(serene orchestral music) - [Narrator] Today, the remains of these giants litter the ground in eastern Montana, (serene music continuing) (footsteps) a playground for paleontologists like Eric Lund, who wants to learn more about how these icons met their end.

They're the last vestiges of the dinosaur rule.

They were making a good go of it, and it just got cut short.

- [Narrator] It came from outer space, an asteroid the size of Mount Everest smashing into the Atlantic Ocean off Mexico.

An event often thought of as wiping out the dinosaurs in an instant.

(meteor crashing) (pterosaurs crying out) But the truth isn't nearly so simple.

- I'm sure some of them got obliterated, the ones very near the impact.

(insects buzzing) (water rushing) But here in Montana, we're far away from where that impact hit.

So they could have lasted hundreds of years after that impact.

- [Narrator] Eric's drafted in paleontologist Michael Pittman.

Michael has built a high-powered laser that highlights different elements in rock.

- [Michael] The laser's essentially giving us chemical information from the rocks that otherwise we wouldn't be able to find with existing technologies.

So this is the image that we have.

Ah- and you'll see... notice how there's this layer.

- [Narrator] This faint line is rock rich in iridium.

- [Eric] And iridium doesn't naturally occur often on Earth.

(powerful percussion music) (meteor whooshing) (meteor exploding) - [Narrator] It was in the days and weeks after the asteroid hit that the deadliest damage occurred.

(deep rumbling) (dramatic orchestral music) Several trillion tons of rock were ejected into space.

(whooshing and rumbling) Rock that rained down on the land below, leaving behind a band of iridium that's now been found in over 100 different locations, proof...that the asteroid's impact (debris falling) affected the entire planet.

(blowing and crashing) - [Eric] The huge cloud of debris and ash would've blocked out the Sun for maybe many months, maybe years.

Would've been like nuclear winter.

- [Narrator] The loss of the Sun was the real killer.

(fire crackling) (footsteps) A planet plunged into darkness.

(fire raging) - [Eric] Well, you block out the Sun, so you start killing off the plants.

And you got no plants, so you get no plant-eaters 'cause they got nothing to eat, and then the meat-eaters can't survive.

Would've been a relatively slow process.

(eerie orchestral music) It wasn't an instantaneous event.

- [Narrator] Eventually, decades after the asteroid struck, over 75% of life on Earth was lost forever.

(dinosaurs rumbling) - [Eric] It's possible, without that asteroid impact, things could have been completely different, and dinosaurs could have lived for another 180 million years.

(sorrowful string music) - [Announcer] In Episode Six, we follow a love story between two Lusotitans who are hoping to grow their family.

(serene string music) - [Narrator] Central Portugal.

(serene music continuing) Buried here are the remains... of a colossus, (tools clinking and scraping) a monumental long-necked Lusotitan.

He's one of the largest dinosaurs ever to have lived, and using his bones, we can begin to imagine this giant's story.

(intriguing orchestral music) In the late Jurassic, a small landmass known as the Iberian Meseta, that one day will include Portugal... lies surrounded by ocean.

(dinosaur rustling) Here, if you're in luck, (crunching and chewing) an easy lunch can be found.

(dinosaur growling) - [Announcer] This Torvosaurus was 30 feet long and stood at 10 feet tall.

They were known as the island's top predator.

(Torvosaurus roaring) - [Narrator] But even these four-ton carnivores (intense orchestral music) (dinosaurs growling and roaring) are no match for the enormous Lusotitan "Old Grande."

(Old Grande growling) - [Announcer] Lusotitans were the undisputed kings of the island.

Old Grande, in Episode Six, weighed a staggering 40 tons and was 33 feet tall!

(rousing orchestral music) - [Narrator] He's been drawn to the beach by the allure... of a female.

(romantic orchestral music) (Old Grande rumbling) As an aging male, (waves lapping shore) this may be his last chance to mate.

(romantic music continuing) (Old Grande vocalizing) Old Grande is one of the tallest of his species ever found, which is certainly one way... to impress a mate.

(majestic orchestral music) (Lusotitans rumbling) (orchestral music continuing) (insects buzzing) (Lusotitans vocalizing) But it's not all about him.

(gentle string music) (powerful percussion music) Although this contender may be younger than Old Grande, (Lusotitans grumbling) he's not afraid to challenge him for the attentions of the female.

(Lusotitans growling) (powerful music intensifying) (Old Grande thudding) (Lusotitans growling) The surprise attack leaves Old Grande seriously hurt.

(Old Grande grunting) (Old Grande breathing heavily) He can only watch (waves crashing) (heavy footsteps) as the rival takes his place at the female's side.

(Lusotitans rumbling) (waves lapping shore) As the days pass, Old Grande rests.

(Torvosaurus grunting) The Torvosaurus risks an approach.

(tense orchestral music) (dinosaurs growling) (Torvosaurus roaring) (Old Grande roaring) (Torvosaurus roaring) A close call.

(dinosaurs rumbling) At long last, (waves crashing) Old Grande's leg is finally on the mend.

(soaring string music) (Old Grande rumbling) And he has unfinished business-- (Old Grande exhaling) finding the female that left him behind.

(string music crescendoing) - [Announcer] Lusotitans had speeds of four to five miles per hour, and it's thought they could keep up this pace over huge distances.

Through their stomps, they sent powerful seismic waves through the ground.

(Old Grande stomping and rumbling) - [Narrator] Many miles away, (female vocalizing) she feels the earth move, (female vocalizing) and she answers... (heavy footfall) her suitor's call.

(romantic orchestral music) (thunder softly rumbling) Reunited at last.

(Lusotitans rumbling) (distant growling) But the moment... (growling continuing) is short-lived.

(Lusotitan roaring) The rival male has stayed close.

(thunder crashing) Each bull uses his colossal weight (dinosaurs growling) (smashing) as a battering ram.

(dinosaurs growling and roaring) They use their teeth to inflict intense pain.

Taking his chance... (roaring) the rival pins Old Grande.

(thunder rumbling) (Lusotitans growling) But this time... (dramatic percussion music) Old Grande refuses to go down.

(Lusotitans growling) (crashing) (Lusotitan wailing) A decisive victory.

Like many birds today, (Lusotitan stomping) it's thought he would use his long, lightweight neck and flexible tail in an elaborate courtship display.

Staying in sync with each other's moves (rousing orchestral music) will be crucial to proving they're compatible.

(Lusotitans stomping) (Old Grande bellowing) Just like modern birds, such as frigates, (sac expanding) Old Grande may have had an inflatable sac to attract attention.

(Old Grande vocalizing) (rousing music continuing) It seems to have worked.

(rousing music crescendoing) (Lusotitans rumbling) (music softly concluding) And so just maybe, with her, he was able to secure his legacy-- (romantic orchestral music) -- a batch of giant eggs.

(romantic music continuing) (dirt softly falling) (insects buzzing) (romantic music continuing) Buried safely beneath the ground, (romantic music continuing) this next generation of Lusotitans (eggs softly cracking open) will soon begin their own story.

(eggs softly cracking) (inspiring orchestral music) - [Announcer] Thank you for joining us on this comprehensive journey through "Walking with Dinosaurs."

The stories of Clover, Sobek, George, Rose, Albie, and so many others transported us back millions of years to a different era, and truly allowed us to "walk with dinosaurs."

We hope you felt like part of the team with these incredible international paleontologists as they uncovered some of the secrets of this magical time.

This has been "Walking with Dinosaurs: A Viewer's Guide."

(inspiring orchestral music concluding) (inspiring orchestral music) (orchestral music crescendoes and fades out)