♪ Male narrator: Over 66 million years ago... ♪ [Dinosaur screeches] Our world was ruled... [Dinosaur grunts] ♪ By dinosaurs.

[Low, guttural growls] [Dinosaur squeals] ♪ The largest animals that have ever walked the earth.

[Growling] ♪ Today, dinosaur experts across the globe are uncovering the bones they left behind.

♪ Allowing us to imagine how these creatures may have lived.

♪ [Utahraptor chitters] [Growling] So that we can tell their stories... [Dinosaur shrieks] And they... [Dinosaur groans] Can walk again.

♪ ♪ Western Canada.

♪ Today a majestic landscape of snowcapped peaks, turquoise lakes... ♪ and mighty rivers... ♪ that erode the ancient bedrock... the perfect conditions for dinosaur hunting.

♪ Here on the banks of Red Deer River, [Tapping] paleontologists from the University of Alberta... are unearthing the final resting place of a super predator.

Man: Oh, wow.

Yeah, that's really nice.

A toe claw.

Wonderful find.

Narrator: Albertosaurus, T. Rex's deadly cousin.

♪ These are the remains of a teenager.

♪ The team calls her Rose.

Man: Holy cow.

It keeps going.

Narrator: Inspired by their discoveries... ♪ we can imagine her story.

♪ In the late Cretaceous, North America is split in two by a vast inland sea.

♪ On its Western shores, a sprawling expanse of dense forests and rugged coastlines.

♪ Laramidia, a land in crisis.

Atmospheric changes have forced temperatures down by two degrees Celsius.

♪ A seemingly small change but enough to push the delicate eco-system out of balance.

♪ [Chittering] [Screeching and squawking] Food is scarce.

♪ Even for an apex predator.

[Growling] Standing 8 feet tall with the weight and power of a full-grown rhinoceros... this is Rose... the Albertosaurus.

♪ It's been a week since she last ate... ♪ but in her sights, an Arrhinoceratops.

Like all 4-legged dinosaurs, it's a plant eater.

♪ A chance for Rose to satisfy her hunger.

♪ [Arrhinoceratops groans] Rose might just be the fastest land predator on the planet... [Arrhinoceratops grunting] Sprinting at up to 30 miles an hour.

♪ [Guttural growling] [Hisses] But Rose has miscalculated.

[Guttural growling] At two tons, her target is twice her weight, with horns 3 feet long.

[Guttural growling] [Hisses] Rose is starving.

[Growling and hissing] But the risk of injury is just too great.

♪ Dinner will have to wait.

♪ [Soft, resonant growling] 71 million years later, dig co-leader Mark Powers... Mark: Hey, guys, how's it going?

Woman: Hey, Mark, look at this.

Narrator: Works with fellow paleontologists from the University of Alberta, world leaders in Albertasaurus research.

Woman: Found new bones.

Mark: Whoa, no way.

Narrator: Rose is almost perfectly preserved.

Mark: You couldn't ask for better, Woman: No.

Mark: better separation.

Woman: You really couldn't.

Narrator: Each day, more remains emerge from the ground.

All: Whoa, oh my god.

Mark: Yeah, yeah.

Clean it off.

Woman: There it is.

Mark: Yeah.

Narrator: Today's discovery, Rose's leg bones.

Oh, that's so cool.

♪ Narrator: Each fossil is exposed and restored, allowing the team to delve deeper into the story of this long-lost super predator.

This is looking really good.

Narrator: Mark works with limb specialist Christiana Garos to examine the bones from Rose's shin.

The tibia is not actually that huge, compared to some of the bigger ones I've seen at least.

Narrator: Albertosaurus is an older relative of Tyrannosaurus Rex.

At about 2 1/2 feet.

OK. Something like that.

Narrator: But it's becoming clear she was a very different beast to her more famous cousin.

So, long limbs, but the ones of T. Rex are quite a bit bulkier, aren't they?

Absolutely.

Rose kind of really embodies what Albertosaurus is.

It's a very legsy animal, especially compared to things like T. Rex, which was incredibly huge, incredibly chunky.

Yeah.

Quick, fast, dangerous, still has powerful jaws.

Maybe the optimal amount of scary for my taste, that's for sure.

Absolutely.

[Chuckles] Narrator: But speed was far from the only weapon in the Albertosaurus arsenal.

♪ More bones are coming out of the ground.

Man: Oh, that's bone.

Narrator: But these don't belong to Rose.

It does look like a bone from one of the digits.

And that's definitely Albertosaurus, right?

Yeah, absolutely.

Narrator: And each bone seems to come from a different-sized Albertosaurus.

Mark: This is a huge one.

[Indistinct chatter] Narrator: Dinosaur hunters have discovered as many as 26 individuals buried here.

♪ To try and say any piece belongs to any one individual is kind of tough to do 'cause there's so many of them.

♪ It's clearly mass grave of Albertosaurus where many individuals died together in this spot.

Narrator: And if they died together...

They likely lived together, too.

♪ Perhaps for Albertosaurus, hunting is normally a team sport.

[Albertosaurus groans] In the cave Rose calls home, she's far from alone.

♪ [Sniffs, then growls] ♪ Albertosaurus are social animals.

♪ They live and hunt together, forming strong, intimate bonds.

[Soft, resonant rumbling] Rose has paired with this male Albertosaurus the same age.

♪ A source of comfort in times of scarcity.

♪ It's been over a week since the Albertosaurus last made a kill.

♪ And starvation isn't the only threat hanging over Rose.

[Rumbling] [Growling] The matriarch.

[Growling] Racked with intense hunger, she could turn on her own.

[Rumbles] And Rose is bottom of the pecking order.

♪ [Growling] If she hopes to survive, she'll have to prove herself when it matters most.

[Soft, resonant rumbling] It's time to go hunting.

♪ Ready?

Man: Let's go.

♪ Narrator: Mark's teamed up with dinosaur anatomy specialist Henry Sharpe.

♪ They're venturing further up Red Deer River on the hunt for more giants.

There's some wonderful prospecting rocks up there.

♪ Narrator: They reach an ancient river system, dating from the same time period as Rose.

♪ And the first clue... Henry: We got a rib here.

Narrator: To what might have fed the Albertosaurus pack.

Given its cross section and its size, maybe Edmontosaurus.

I'd say Edmontosaurus, yeah.

♪ Narrator: Edmontosaurus.

A plant-eating, duck-billed dinosaur.

♪ Edmontosaurus can get up to 30 feet long, 10 meters here.

Jeez.

Yeah.

These things were huge.

♪ Narrator: But a single Edmontosaurus wouldn't feed a hungry pack of Albertosaurus for long.

♪ Mark: Holy cow.

♪ Henry: Oh, my God.

Narrator: At the top of an escarpment... Look at the size of these honkers.

Narrator: More fossils.

Not bone but footprints.

♪ You can see they got the big front toe and the two toes on the side and it's much wider than it is long, which is classic Edmontosaurus duck-billed dinosaur.

♪ Narrator: From the pattern of these prints, it looks as though these trackways couldn't have been made by a single creature.

♪ Mark: I got about 16, 17 tracks exposed here.

Narrator: Today, there are just a few footprints, but when they were created, there would have been many, many more.

Mark: We have lots of footprints from various different individuals, various different ages all congregating together, so they definitely moved in herds, lived in herds.

Henry: Yeah.

You imagine, like, herds of wildebeest and these animals were the size of one to two elephants.

♪ Narrator: These fossilized footsteps suggest this corner of Canada once played host... [Deep, bellowing calls] To one of the most remarkable sights in Earth's history.

♪ A migrating Edmontosaurus herd.

[Bellowing] Thousands of plant-eating dinosaurs moving as one.

♪ [Huffs] [Bellowing] But an individual adult Edmontosaurus can be 3 times the weight of even the largest Albertosaurus.

[Bellowing] [Insects and birds chirping] [Dinosaur rumbles] ♪ Working as a pack is the only way to take down such colossal prey.

♪ [Dinosaur bellows] ♪ Higher ground will provide the perfect vantage point... [Hisses] To mount an attack.

♪ At this time of year, this area should be teeming with Edmontosaurus.

♪ But the herds are nowhere to be seen.

♪ [Growl] ♪ This is a time of intense geological upheaval.

♪ As the continents move... ♪ The land buckles and splits.

♪ Lava and ash engulf the landscape... [Deep bellowing] Forcing this Edmontosaurus herd to take a much longer route north this year.

[Growls] [Young Edmontosaurus whines] ♪ They're still many miles away from the starving Albertosaurus.

♪ For the pack, the delay spells disaster.

♪ [Rose whines] But on the horizon... [Dinosaur screeches] Rose spots an opportunity.

♪ From the wind-carved rocks by Rose's dig site, paleontologist Carlton Copick has made an important discovery.

♪ Yeah.

So here's a bit of the shaft.

Narrator: Tiny fragments of finger bone belonging to one of the most bizarre creatures of the Cretaceous.

And here's the condyle.

-What?

-So it looks like it might be from a digit.

-There's a condyle?

-Yeah.

Narrator: Including a rare condyle, part of the knuckle joint.

Very nice.

I'm afraid to touch it.

It's just so small and so delicate.

Yeah.

You can see the internal structure of the bone right there.

Narrator: The fossil's paper-thin exterior tells Mark this bone was built for flying.

♪ But this was no bird.

Even in birds, the bone is usually a lot thicker on the outer surface.

This is very strange.

[Chuckles] Narrator: It can only belong to one creature.

♪ [Squawking] A colossal flying reptile [Dinosaur screeches] with a 20-foot wingspan.

♪ Cryodrakon, a giant pterosaur.

♪ They feed on an enormous anamite washed up on the spring tide.

♪ [Squawks] ♪ The Cryodrakon would make a fine meal for Rose and her mate.... if they can catch one.

♪ [Snapping] [Squawks] ♪ Approaching from downwind and with the pterosaur's attention on their meal, the youngsters close in.

[Huffing] ♪ [Gulping] ♪ [Screeches] [Shrieks] ♪ At last a chance to feed.

♪ But the pair's absence from the pack... hasn't gone unnoticed.

[Soft, resonant rumbling] ♪ Life in an Albertosaurus pack was fraught with brutality.

♪ And 71 million years later, this violence is still written in the bones.

♪ Mark and anatomist Greg Funstone examine the jaw bones of one of the largest Albertosaurus ever discovered.

We do actually get a few scars along here and they're kind of evenly spaced.

Some are raised and some are deep gauges.

So could these be bite marks?

Narrator: An astonishing 65% of Albertosaurus skulls found here have teeth marks scratched into the bone itself.

♪ Near your finger, there's a little gouge in that one, too.

Mark: Look at that.

Greg: That's deep.

Yeah.

It actually looks like the tooth came down from over the top.

That would have required tremendous amount of force from this diving angle to actually remove that piece of bone.

Narrator: Only another Albertosaurus could inflict this injury.

♪ Greg: The biggest predator in this ecosystem and it's still getting beaten up day to day.

They're maybe tussling for food like you see on the Savannah today where lions will eat in a certain order.

You got two hungry Albertosaurus, one of them is gonna wanna eat first.

Only one can.

♪ [Crunching] ♪ Narrator: As pack leader... ♪ the matriarch is eyeing up the youngster's kill.

[Growling] Rose is determined to defend her prize.

[Growling and hissing] But the matriarch leaves her in no doubt who's in charge.

[Rumbling] [Huffing] [Growling] [Crunching] [Hisses] Narrator: Hungry and badly wounded, Rose has learnt a painful lesson.

♪ She'll have to play by the rules if she wants to survive.

[Tapping with hammer] But the evidence coming out of the ground suggests not all of the Albertosaurus behavior was violent.

Mark and Henry examine one of the most intriguing discoveries.

Rose's tiny, fossilized arm bones.

♪ So we got the, the upper arm here and the forearm down there, around and up here this is the hand, right?

This is like the palm of the hand.

Narrator: Nobody's quite sure what Albertosaurus used its minuscule arms for, but the strange positioning has given Mark an idea.

Mark: It's quite possible the resting position of the arm was to have a more flared fingers, sticking outwards rather than, you know, kind of down by the side like a chicken wing.

So this was my arm, it would kind of be flared out like that.

Yeah, you'd be kind of doing one of these things.

Almost jazz hands.

Yeah, exactly.

So Albertosaurus is clearly using its arms for something.

I mean, modern birds have a wide variety of mating displays and behaviors.

Mm-hmm, yeah.

Narrator: Mark believes these seemingly useless arms may have been vital tools for bonding.

So if you're gonna live in a group, you've got to have ways of communicating with one another that go beyond just, you know, grunting and staring at each other, so maybe they're using their hands side by side on the flank, reassuring one another.

Telling each other it's gonna be OK, it's fine.

For morale boost.

Yeah.

Yeah, exactly.

♪ [Huffing and snorting] Narrator: Starving, shaken, and badly wounded... Rose needs comfort.

[Growls] ♪ The young Albertosaurus take time out together to groom.

♪ A soothing ritual... [Soft, resonant rumble] That strengthens their bond.

♪ Whatever the future brings... ♪ They will face it...together.

♪ [Soft rumbling] ♪ As a new day dawns... ♪ the pack's luck may be about to change.

♪ [Huffing] ♪ The Edmontosaurus have finally made it to their summer feeding ground.

♪ Not a moment too soon for the starving Albertosaurus.

♪ And despite their young age, Rose, her mate, and the other youngsters will play a crucial role in the hunt.

♪ The fate of the whole pack depends on them.

♪ Close to Rose's dig site, a remarkable new fossil is emerging.

♪ Henry: Wow.

Very cool.

♪ Narrator: An Edmontosaurus jawbone.

Maybe this is the dentary going in here.

That could be the back part, yeah.

Narrator: But this fossil holds another secret.

Mark: What have we got up here?

Henry: That looks like enamel.

Look here.

Serrations.

Henry: That's incredible.

♪ Narrator: This is no Edmontosaurus tooth.

♪ This came from a meat eater.

Mark: Albertosaurus tooth.

I think you're right.

And since we don't have much of the root, it was probably lost during feeding.

That is an awesome find.

♪ Narrator: It's clear evidence that the Albertosaurus pack did feast on Edmontosaurus.

[Tapping with hammer] But it doesn't help explain how they bought down such enormous prey... And what role Rose might have played in the hunt.

♪ Man: Yeah, should be.

[Tapping] These are Rose's metatarsals from the right leg.

Quite narrow and compact for an animal that people usually envision as being huge, huh?

♪ Narrator: Mark and Christiana investigate Rose's foot bones.

They get a heck of a lot bigger.

Narrator: Comparing them with the outer foot bones of a fully grown adult.

♪ While they're similar in length, they're a very different thickness.

So we can see this one is only about one, 1 1/2 inches in width, whereas we look at this one, we have almost double that, so it's about 2 1/2 inches in width.

Absolutely a beast, and the same thing can be said about the other metatarsal.

♪ Narrator: Rose was almost as tall as the largest Albertosaurus but just half the weight.

She was definitely going to be much more agile and quick than these big individuals, which probably had a lot more difficulty picking up speed.

♪ Narrator: Large Albertosaurus were unlikely to reach high speeds due to their enormous weight.

♪ Meaning Rose and the other youngsters must take on the most dangerous of jobs.

[Birds chirping] [Soft rumbling] Narrator: Rose and her mate split off from the pack.

As the swiftest runners, they must identify a target... And separate it from the herd.

♪ [Bellowing] But they're a fraction of the weight of the largest Edmontosaurus.

♪ Impulsive and inexperienced... Rose's mate blindly charges into the herd... [Bellows] [Growls] Trying to take down one of these enormous creatures alone.

[Snarls] [Bellowing] [Rumbles] [Edmontosaurus bellows] [Heavy wheezing] ♪ Rose has lost her closest companion.

[Soft rumbling cry] And each failed hunt brings her and the rest of the pack closer to starvation.

♪ [Pick striking] [Birds squawking] [Tapping with hammer] But Albertosaurus were successful even in times of adversity.

♪ They were the dominant predator in Western Canada for over 3 million years.

♪ At Rose's dig site, part of the reason behind their success might be emerging.

[Blows] This bit right here.

Narrator: An unassuming fragment of bone.

Mark: Well, it looks interesting.

Henry: I thought it was a rock, actually.

But it's got a pretty interesting texture, it looks like Albertosaurus and this roughened area looks to me like the border of an eye socket.

Narrator: Is this a part of Rose's skull?

♪ Mark: That is part of the skull.

It's probably an indication that the skull is in several pieces at least, so we'll have to keep our eyes out for any loose skull bones that might be scattered about amongst the site.

[Tapping with hammer] [Wind howling] Man: Whoa.

Christiana: It's Rose's ghost.

♪ Narrator: The team estimate Rose's skull would have been about two feet long.

Big but not big enough to take down huge prey like Edmontosaurus.

♪ But maybe she didn't have to.

Mark and Carlton re-examine the jawbones of one of the largest Albertosaurus.

Just look how big and robust this jaw is.

It's absolutely crazy.

Looks like there's quite a few tooth sockets on this side.

Narrator: It's the final piece of the puzzle, revealing the pack's sophisticated hunting strategy.

Altogether, 68 teeth in the jaw.

Lots of points of, of entry into the body, so basically instead of using the arms to grapple with prey, it's all about the head.

♪ Narrator: These jaws were built to apply brutal force.

A bite force that's probably upwards of several tons, there's not much that can, you know, protect itself from that, once they have their eyes on you.

Yeah.

♪ Narrator: Rose's speed and the bite force of these bigger animals make for a deadly combination.

♪ Could say that Rose was the runner and this was the muscle.

When Rose got the animals out on their own, big predator like this probably would have come out and just finished the job.

[Birds and insects chirping] [Bellowing] [Rumbling] Narrator: Rose may have lost her mate but she must now work with the other youngsters to find the easiest target.

♪ But with one failed hunt already, the pressure is on.

♪ [Snorts, bellowing] [Bellows] Rearing up on their hind legs, the Edmontosaurus are too powerful.

[Bellowing] But Rose bides her time.

Until she spots an older individual.

[Huffs] One that might be weaker than the others.

♪ [Growling] [Rose hissing] [Bellows] Rose can't take this Edmontosaurus down alone.

♪ But she can steer her prey... ♪ right towards the killing jaws of the matriarch.

♪ [Bellows] [Growls] But there's still fight in this old bull.

[Growling] [Deep, bellowing cry] [Growls] [Bellows] [Groans] ♪ Rose has played her part to perfection.

Finally the pack can feed.

♪ And this time... Rose gets her share of the spoils.

[Crunching] ♪ Woman: All right, who's ready to jacket?

Coming your way.

Mark: Grab those.

Narrator: The team is eager to get their finds back to the lab... to learn more about this extraordinary creature.

[Liquid dripping] They carefully wrap their discoveries in protective plaster.

Woman: All right, everyone in the vicinity is going to receive plaster on their clothes and body, so.

♪ Man: 1, 2, 3.

Woman: Ohh.

Man: It's OK, it's OK.

There's lots of rock, there's lots of rock.

Narrator: They flip them, ready for transport back to base.

Mark: Perfect.

Beautiful.

Now just the third one.

♪ Mark: Go, flip.

Woman: Watch your feet, watch your feet.

Narrator: But some of Rose's remains are too heavy to carry down the hillside.

So Mark has called in a little help.

Woman: Ah, love that sound.

[Helicopter whirring] Hold on to your hats.

♪ Narrator: One false move and all the team's work would be destroyed.

[Helicopter whirring] With ropes attached... ♪ Rose soars through the air.

[Indistinct chatter, cheers] ♪ But these ancient lands hold one final surprise for the dino hunters.

Mark: What have you got there, champ?

Narrator: Carlton has made a once-in-a-lifetime discovery.

Man: Oh, what?

Christiana: Wait, hold on, that's a...what?

Narrator: A tiny jawbone.

♪ Christiana: What's this a jaw of?

Mark: It's an Albertosaurus.

Christiana: It's so tiny.

Narrator: This is a baby Albertosaurus.

Woman: Oh, that's beautiful.

Man: Like a baby.

Yeah, probably only about a year old.

Think this is the youngest individual we have.

♪ I mean, I had to put it down for a sec to make sure I wasn't hallucinating.

[Christiana laughs] Carlton: Just scratch it like a puppy.

Woman: Yeah.

[Laughs] Narrator: It's more evidence of the success of the Albertosaurus.

[Dinosaur bellowing] ♪ And maybe the baby belonged to one of the pack females.

♪ Perhaps even Rose herself.

♪ [Soft rumbling] Narrator: As to how Rose died, we may never know.

Show and tell time.

Narrator: Causes of death rarely fossilize.

Woman: So cute.

Man: That's awesome.

Woman: Well, the comparison really pulled it.

Man: Yeah, yeah.

It's not even as long as the tooth.

Man: Oh, my... [Woman laughs] ♪ Narrator: And though her death is a mystery... ♪ Now at least we can tell the story of how she may have lived.

[Huffing] [Soft, resonant rumbling] Rose, the young Albertosaurus... Earned her rightful place...

Hunting and surviving... with her pack by her side.

♪ [Birds and insects chirping] ♪ [Edmontosaurus bellowing] Narrator: 71 million years ago, in what would become modern-day Alberta... ♪ Thousands of Edmontosaurus ruled over this lush landscape... Of vast plains and meandering rivers... [Albertosaurus rumbles] With deadly Albertosaurus stalking their every move.

♪ Henry: If you're looking for a good meal, they were just giant walking piles of muscle, the McDonald's of the Cretaceous.

♪ Narrator: Edmontosaurus were one of the most dominant plant-eaters on the continent.

♪ Henry: If you think of wildebeests in, uh, Africa right now, that's Edmontosaurus because they're everywhere here.

♪ Narrator: Paleontologist Henry Sharpe thinks they had a surprising survival tactic.

A vital key to their success.

Did Edmontosaurus abandon their defenseless young?

Henry: Basically the animal, it was sitting on its belly, right?

And then the different parts kind of fell to the side.

Narrator: The team has discovered the final resting place of a youngster they've nicknamed Gary.

Gary is a juvenile Edmontosaurus.

He would have been about 4 meters long, and what we found mostly is the body, parts of the skull, and the tail.

♪ Narrator: Gary's bones are seemingly alone, a long way from any adult Edmontosaurus.

And for Henry, that poses a mystery.

♪ Experts believe Edmontosaurus grouped together in herds... ♪ Allowing them to close ranks... And protect each other from marauding predators.

[Wails] And so living in groups means that you could have one or two animals kind of looking out while the rest feed.

It's like a meerkat strategy.

♪ Narrator: But despite being social animals, the team hasn't found adults and youngsters buried together.

It's just adult Edmontosaurus in one spot and baby Edmontosaurus in another spot.

[Birds and insects chirping] Narrator: Edmontosaurus young were about the size of a small dog and almost defenseless.

[Young Edmontosaurus whines] Henry: Juveniles are just kind of running around beneath your feet.

They're hard to take care of if you're the size of two elephants.

[Bellowing] Narrator: And that's not all.

Henry thinks young Edmontosaurus hadn't yet developed a defense feature found in adults.

Henry: The juveniles, the eye sockets face very much to the side, um, but in adults, this bone right behind the eye actually inflates, there's a big sinus in it, and that pushes, uh, the eye sockets to rotate to face forward a little bit more.

♪ Narrator: Adult Edmontosaurus eyes pointed forwards.

♪ This means they could spot an approaching Albertosaurus pack... ♪ Track its approach, and act fast.

[Huffs] Henry: If you want to avoid a fast predator like Albertosaurus, maybe what you need to do is spot it from a long way away, 'cause then you can get a head start.

You need to get your herd together and move out.

[Bellows] [Snarls] Narrator: But with eyes on the sides of their heads, younger Edmontosaurus wouldn't spot danger quickly.

[Soft, nasal wails] Small, defenseless, and unlikely to spot predators.

This doesn't seem like a recipe for success.

But Henry thinks Edmontosaurus had a clever solution to ensure the next generation survived.

♪ Whilst the very youngest may have stayed with the herd, at a certain age, the juveniles go it alone.

Henry: Yeah, Edmontosaurus are growing up kind of alone, probably sticking to the forests and away from the big open river plains where the Albertosaurus are waiting to, to eat them.

[Roars] Narrator: Henry thinks this strange finding could be the secret to the species' success.

Henry: For some reason, uh, them abandoning their young is the way to go.

It's the one that's helping most Edmontosaurus reach maturity.

It's a weird strategy but it's what they did and it's what has worked.

Narrator: If Henry's right, this strategy helped Edmontosaurus become one of the most abundant dinosaurs in North America.

♪ In just a few years, juveniles like Gary would be the size of an elephant and armed with life-saving binocular vision.

♪ Finally ready to rejoin the herd.

♪ Next time.

A toddler makes a perilous journey.

[Screeches] Joining one of the largest dinosaur herds [Growls] that ever lived, in its fight for survival.

[Growling]