BBC Dinosaur Planet (2011) s01e03 Episode Script

Last Killers

We're living through THE golden age of dinosaur discoveries.
From all over the world, a whole new generation of dinosaurs has been revealed.
From the biggest giants and the deadliest killers to the weird and the wonderful.
from the Arcticto Africa.
From South America to Asia.
Using the latest evidence, for the first time we have a truly global view of these incredible animals.
In this episode, we explore the last generation of killer dinosaurs .
carnivores that took killing to a new level.
At the end of the Cretaceous period, 75 million years ago, these hunter-killers had spread throughout the globe.
In the southern continents, it was the powerful and muscular Abelisaurids that reigned supreme.
Whereas in the north, it was the famous Tyrannosaurs that dominated.
75 million years ago, the Dinosaur Park formation in Canada was home to two of the largest Tyrannosaurs.
The biggest and heaviest was Daspletosaurus.
In 2009, medical scanners were used to look inside the brain cases of these killers.
Of all the dinosaur groups, Tyrannosaurs were discovered to have one of the largest areas devoted to smell something that would give them a clear hunting advantage.
Back then, Cretaceous Alberta was a vast coastal river plain covered in forests .
the perfect hunting grounds for Daspletosaurus.
At nine metres and three tonnes, it's the dominant predator in these forests.
Here, it relies on its acute sense of smell and hearing, as much as its sight, to hunt its prey.
Chasmosaurus, a rhino-sized behemoth, bristling with defensive horns .
and an opponent befitting a killer like Daspletosaurus.
Of all the tyrannosaurs, T Rex might be the most famous, but the evolutionary blueprint for these predators was laid down 10 million years earlier, with Daspletosaurus.
Tyrannosaurs' effectiveness as killers is clear from their anatomy.
They're massive, with huge, strong skulls, and powerful muscular necks.
Forward-facing eyes make tracking moving prey easy.
They've famously short arms, but with these giant Tyrannosaurs, it's all about the bite.
They had the most powerful bite of any dinosaur with teeth that, unlike the thin, flesh-tearing blades of Carnosaurs, are thick and strong, easily able to crush bone and kill.
However, this Daspletosaurus has lost the element of surprise.
The odds are now stacked in the Chasmosaur's favour.
Even the most deadly predators fail more often than they succeed.
Tyrannosaurus appeared locked in a deadly evolutionary arms race with the horned dinosaurs.
As one got bigger, so did the other.
It's a predator-prey relationship that endured for more than 65 million years.
Most striking are the head frills of the horned dinosaurs.
The imposing frill of Chasmosaurus is actually made of thin bone and wouldn't stop the bite of a Tyrannosaur.
But by making it look much bigger, it had the desired effect.
The horns and frills of these dinosaurs acted as visual deterrents, even if they offered little physical protection.
It meant that a fully grown Chasmosaurus would usually be safe from most predators.
This Daspletosaurus is just a youngster.
Even two Daspletosaurs pose little threat.
But in 2005, a remarkable discovery was announced.
In the Two Medicine Formation of Montana, a new dig revealed had unearthed something quite extraordinary a collection of Daspletosaurus fossils, all buried at the same place at the same time.
The implication is that Daspletosaurus hunt in gangs.
Tyrannosaurs, like Daspletosaurus, were so successful that, by the late cretaceous, they were the apex predator across virtually all of North America and Asia.
In Asia, there was Alectrosaurus, Alioramus and Tarbosaurus.
In America, Albertosaurus, Gorgosaurus, Daspletosaurus and T Rex.
But moving further north, evidence of Tyrannosaurs becomes increasingly rare.
In Alaska, fossils have been excavated close to the Arctic Ocean.
It's the richest source of dinosaurs that lived in the polar regions and it seems here, a different type of killer dominated.
The most common plant-eater in this region is the highly social Edmontosaurus.
They're the largest duck-billed dinosaur in North America .
and they are the perfect prey for a very different type of predator.
Troodon may not look as lethal as a Tyrannosaur, but fossil evidence suggests that these too were deadly hunters surviving entirely on a diet of meat.
At first sight, it appears the adult Edmontosaurus have little to fear.
12m in length and weighing 3.
5 tonnes, they physically dwarf this diminutive predator.
Troodon were usually small, two-metre dinosaurs but the teeth from the Alaskan Troodon showed something remarkable.
These Arctic predators were almost twice as big as normal.
Troodon not only survived here, they positively thrived.
And that's because their hunting prowess comes into its own after sunset.
This is a land where, after late summer, there are more hours of darkness than light.
Troodon famously have the largest brains relative to their body size of any dinosaur .
although what appears more important are their eyes.
Not only are they forward facing, making them active hunters, but they are exceptionally large.
These are predators that can hunt equally well after dark.
Although the group offers protection, predators always choose the easiest prey, so it's the juvenile Edmontosaurs that are at risk.
Separated from the group, this youngster has made a dangerous mistake.
The Alaskan dinosaur bone beds are dominated by juvenile Edmontosaurus remains.
Some show clear evidence of Troodon bite marks.
It seems, despite its small size, Troodon thrived here by exploiting the vulnerability of the juveniles throughout the long, dark, winter months.
With a steady food supply, it means Troodon can survive the harsh Arctic winters.
And, in doing so, grew to almost double the size of their cousins further south.
But these were the exception.
Wherever else Tyrannosaurs lived, they were the largest predator, living in groups that consist of both youngsters and adults.
In these deadly packs, youngsters provide the speed, adults the power.
It's a hunting strategy that they use to deadly effect.
But despite appearances, this mob attack isn't carefully planned.
There is no strategy behind the actions of the gang.
It's merely opportunism.
And when the kill has been made, the next battle soon begins.
In many Tyrannosaurs, we find holes and gouges on the skulls, injuries which turn out to be bite marks made by other Tyrannosaurs.
In one Daspletosaurus fossil, the tooth marks indicate that an individual had been subject to several attacks.
In another, the tip of a tooth was left embedded in the bone of its skull.
From this evidence, we can assume that such groups were far from harmonious .
and they certainly aren't democratic.
In this world, the strongest takes all.
Tyrannosaurs' domination of the globe might have been total, had it not been for a strange quirk in the arrangement of the continents.
75 million years ago, the planet had a clear north-south divide, with no physical link between the parts of the globe.
It meant the Tyrannosaurs couldn't spread to the southern continents.
Here, a different type of killer reigned supreme.
These were Abelisaurids.
In the last ten years, Madagascar has provided the most comprehensive evidence about these predators.
70 million years ago, Madagascar was already an island.
But its climate was much hotter and drier than today.
In the Cretaceous period, Madagascar was subject to devastating droughts.
And big predators like Majungasaurus are especially vulnerable to starvation.
Scavenging is the only way to survive.
We thought Majungasaurus was the top predator here.
But then, in 2003, some bones of a number of Majungasaurs were reported gouged with teeth marks.
It appeared there was a bigger, more brutal killer at large.
Majungasaurus also shares the plains with smaller dinosaurs like Rahonavis.
Being smaller means Rahonavis needs less food to survive.
A carcass will attract every big predator for miles around.
A male Majungasaurus, attracted to the feast.
It is more than capable of challenging for the carcass.
Majungasaurus has short arms and can't grasp.
Like Tyrannosaurs, it's all about the bite.
The shape of Majungasaurus' skull and teeth suggests a very different biting style to the flesh-tearing dinosaurs.
With a broad, short and muscular skull it was a dino better adapted to biting and gripping, rather than slashing its prey.
This fight is about more than just winning the feeding rights to a carcass.
When the bite marks on the mauled Majungasaurus remains were studied more closely .
the marks on the bones were found to match the only large carnivore in the region.
There is no bigger killer in these lands than Majungasaurus.
This is the first, irrefutable evidence of dinosaur cannibalism.
It might seem shocking, but it's a behaviour that clearly shows the most successful killers will exploit any situation to their maximum advantage.
With a bite force unmatched by any other dinosaur in the region, these are killers in a completely different league.
And this group have congregated to take advantage of an annual event.
In Dinosaur Provincial Park, thousands of bones have been discovered, scattered across the same rock layer.
They belong to the horned dinosaur Centrosaurus .
and they appear to be the bone beds of vast killing fields, sites of wholesale slaughter.
This vast herd of Centrosaurus are on the move .
from their nesting sites on coastal lowlands to the east.
Unwittingly, they're moving towards almost certain death.
Seasonal monsoons drives the Centrosaurs inland, away from coastal flooding.
It's what the Daspletosaurus have been waiting for.
Herding behaviour protects the many but at the expense of the few.
And things are about to get worse for the Centrosaurs.
With a flooded river ahead and the Daspletosaurus behind, the stage is now set for a massacre.
But despite the rich pickings, it's not the Daspletosaurs that are responsible for the scale of the slaughter.
There's an even more deadly killer at work here.
Severe monsoon rains have transformed shallow rivers into lethal torrents.
The real killer is the weather itself.
Recent studies of this dense bone bed indicate that 96% of the bones are of a single species - Centrosaurus - and relatively few of the bones display any bite marks.
The fossil evidence suggests that this was a mass drowning .
the result of widespread seasonal flooding an event that we have seen repeated in over 20 different sites.
And when the waters recede, new opportunities emerge.
Events like these provide easy pickings for predators.
But even in the fight for rotting flesh, Daspletosaurus's authority is absolute.
Tyrannosaurs in the north and Abelisaurids in the south were the supreme killers of their age.
They dominated every continent where they were found.
And together, they were the last of the killer dinosaurs.