Original subtitles

(mysterious music)

(chirping)

(roaring)

- [Narrator] To study the mammals that lived

during the age of the dinosaurs paleontologists

were dependent for a long time on tiny fragments of fossils.

They believed that mammals of that time were

no larger than a mouse and that they had only flourished

after the extinction of dinosaurs.

But, the discovery in China of amazingly

well preserved fossils at the beginning

of the 21st century revealed that mammals

were bigger and more varied than previously thought.

Detailed analysis of their physical features

allows us to understand how they were able

to co-exist with their carnivorous neighbors

and even outlive them.

(growling)

(roaring)

The fossils of these amazing mammals

were found in the volcanic region

of Liaoning, northeast of Beijing.

Repenomamus was the size of a wolf

and was able to devour young feathered dinosaurs.

(growling)

(hissing)

(thundering)

They must have been victim to large predators

like these Yutrannuses.

They are much bigger than all previously known mammals.

(growling)

These Repenomamus lived 130 million years ago

in a highly active volcanic area.

(dramatic music)

(growling)

Preserved in fine volcanic ash their skeletons

have survived the ages,

(dramatic music)

radically changing paleontologists understanding

of the first mammals.

(barking)

(squealing)

(gentle music)

- These fossil mammals are certainly related

to our own revolutionary history in the sense

that we ourselves, are mammals.

- [Narrator] Mammals, whose name comes

from mammary gland, are the only animals

to suckle their young.

Their characteristics include fur covered bodies,

ears that are separate from their jaws

and a great variety of teeth.

All of which, according to the latest fossil discoveries,

were already present at the time of the dinosaurs.

- What we see is that they go from having teeth

with a few cusps on them to having teeth

that have many different cusps or tools,

such that they were able to survive

the mass extinction that killed off dinosaurs.

- [Narrator] The fossils discovered

at the beginning of the 21st century

show that the first modern mammals appeared

125 million years ago.

The genetic analysis indicates that they may

go back even further.

Until the discovery of new evidence,

controversy rages between geneticists and paleontologists.

It all began 250 million years ago

at the beginning of the Triassic Period

during a time when the world was extremely hot.

The ancestors of the mammals, mammalian reptiles,

like these Trinaxodon, a relative of the reptile family.

Trinaxodon is considered to be a transitional species

in the evolution towards mammals.

Like reptiles its legs are not under its body,

but on the sides and it has no external ears.

But, like mammals, it has several different

kinds of teeth and its body is covered with fur.

To escape the heat it dug burrows along the banks

of rivers which is where it was fossilized.

New x-ray technology at the Synchrotron Radiation Facility

in France enables scientists to analyze

this South African burrow discovered in the 19th century.

(dramatic music)

Using this innovation Vincent Fernandez is able

to study the contents of the rock without destroying it.

- [Translator] We discovered this burrow

on a site where a road was under construction

and amidst all the burrows we discovered

in this small quarry, this one had small bones in it

which gave us the idea of extracting it completely

and studying it here at the Synchrotron in Grenoble.

- [Narrator] This tunnel was buried 250 million years ago

at a pivotal moment in the Triassic Period

when 70% of the planet's terrestrial species disappeared.

This block of stone may be able to tell us more

about what happened to the survivors

of this dramatic extinction.

- [Translator] The best way to find out which animal

used which burrow is to find the animal

directly inside the burrow.

And to find this animal, rather than clearing

the rock by hand, we will use x-rays to study

the animal inside the fossilized burrow.

- [Narrator] 100 billion times more powerful

than hospital x-rays, the synchrotron is able

to distinguish the difference in density

between fossilized bones and the rock itself.

(dramatic music)

This high resolution technology revealed

the presence of a Trinaxodon, a long lost mammal ancestor,

plus, an unexpected bonus, an amphibian

named Broomistega lying by its side.

(dramatic music)

- [Translator] This is a very big surprise

because first of all, we did not expect that.

But mostly, it's very rare because animals

don't usually share the same burrow,

especially with animals that are the same size

and have the same diet.

- [Narrator] Just as some mammals hibernate

to protect themselves from the cold,

this Trinaxodon burrows underground

and aestivates to avoid the heat.

(grunting)

In this dormant state it may not have been aware

of the Broomistega taking refuge in its shelter.

The amphibian could also have been hiding

from the hostile climate

and its fossil shows that it was injured.

- [Translator] We discovered

that the Broomistega was wounded.

It had a series of seven broken ribs

that were healing.

We knew that because it had small bone growths

around the fractures, so we see the healing process.

We know it was probably injured for several weeks.

- [Narrator] This discovery revealed that mammals'

ancestors had developed the ability

to enter into a state of torpor, one wounded,

the other asleep.

Both animals would've been taken by surprise

by the rising waters.

- [Translator] The lineage to which Trinaxodon belonged

was capable of surviving because it could dig

underground tunnels and withstand droughts

thanks to its specific metabolism.

The fact that this lineage survived allowed

for the emergence of mammals several million years later.

(dramatic music)

- [Narrator] Vincent and his South African colleagues

are now searching for new burrows to scan

hoping to solve other mysteries.

- [Translator] We are also looking for an egg

or a pregnant female that will finally tell us

which mode of reproduction our ancestors had.

- [Narrator] It's a difficult task

because mammal fossils from the Triassic Period

are very rare.

(gentle music)

Until the late 20th century

the only remains we had of the first mammals

were their teeth like these tiny specimens

that are preserved at the National Museum

of Natural History in Paris.

Mammal Specialist, Emmanuel Gheerbrandt, remembers

his early years as a paleontologist.

- [Translator] When I started my career in the '80s and '90s

most of the remains we found were isolated teeth.

We dreamt of finding not only jaws,

but complete skulls.

- [Narrator] These tiny fragments are obtained

through painstaking work.

Paleontologists must sieve several tons of sediment

to uncover just a few of these mammalian teeth.

(gentle music)

The teeth are well preserved

because tooth enamel is particularly resistant to time.

It is the hardest part of the skeleton,

the part that fossilizes best.

- [Translator] The interesting thing

about these collections of isolated mammal teeth

is their small size.

You can have a collection of several hundred teeth

which will fit into a shoe box.

So, you can have the representation of a very diversified

fauna even the history of a whole geographical province,

which boils down to a collection in the drawer

of a cabinet with several hundred teeth.

- [Narrator] That's exactly what the collection

studied by Emmanuel Gheerbrant's team looks like.

Started in 1976 in a fossil deposit near Nancy

in Northeastern France, it now contains

close to 1000 teeth from the Triassic Period

210 million years ago.

This is the oldest collection of mammals in the world

with a dozen different species identified solely

through the shape of their teeth.

On these molars the three cusps are exclusive to mammals.

The molars are used to grind food,

while canines keep food in place and incisors cut.

This complex dentition indicates

that these animals are mammals,

since other animal species have only

one type of tooth.

- [Translator] The shape of teeth is like

an identity card to show what group they belong to.

It's an identity card to identify the animal

and it also reveals functional information.

In other words, the animal's diet,

because sharp teeth for instance, indicate

an insectivorous diet, but if they have

rather flattened teeth, that indicates a herbivorous diet.

- [Narrator] Though they tell us more

about how these dinosaur age mammals ate,

the fossils give no indication as to what they look like.

(gentle music)

However, a tiny clue discovered in France

in 2008, reveals more about the skin

of these extinct animals.

This abandoned quarry is located

near the town of Akena on the west coast of France.

On this sand excavation site two paleontologists

from the University of Rennes take advantage

of the exposed walls to come and collect fossils.

This geological layer dates from the Cretaceous Period

100 million years ago.

At the time it was covered by a forest

of conifers and ginkgo trees whose remains

have been uncovered by (speaking in foreign language).

- [Translator] Look at this.

This leaf has been in clay for the past 100 million years.

It comes off and if I blow on it,

I can bend it which shows that it's still flexible.

- [Narrator] Apart from its changing color

the passage of millions of years doesn't seem

to have altered this leaf significantly.

The paleontologists are searching for another treasure

in this petrified forest.

Occasionally, bits of animals become trapped

in the resin from conifer trees.

When the resin fossilizes it becomes amber.

- [Translator] Here we are at the bottom of the quarry.

Water has poured down and created

an interesting down drop because you can see

the different layers.

The layer is streaked because you have

different alternating sediments.

You have two main types of deposits.

You find sand deposits, white, ochre and red

and then another deposit from an accumulation of coal

which forms these small black veins.

So, here you can see sand alternating

with clay beds that can take plant debris

and small pieces of amber, which is what we're looking

for in particular.

- [Narrator] The sediment is then sieved in a nearby pond.

- [Translator] We've got quite a few small fragments here.

- [Translator] That's a good size piece.

It's slightly translucent, part brown, part red.

- [Narrator] Paleontology relies on meticulous work

and a fair amount of luck.

One major clue to the appearance of mammals

was discovered thanks to an incredible stroke

of good fortune.

While looking for bacterial filaments

one of Romain Vulla's colleagues made

an exceptional discovery,

two hairs trapped in amber.

- [Translator] So, we see the whole piece of amber

and in the middle, the longer of the two hairs

which is slightly bent.

As you can see, it is very, very fine.

We compared this 100 million year old fossil hair

with the hair of current mammals

and we found that this one present

many similarities with what can be found

in existing species, including scale morphology

and scale layout.

And the contours also show strong similarities

to the hair of living animals.

From a paleontological point of view

this is an outstanding discovery,

since there are only one or two fossil

mammal hairs in the world.

- [Narrator] 100 million years ago warm blooded mammals

already had the same hair as today

to protect them from the climate

and allow them to survive the extinction

that dissimilated large dinosaurs.

(dramatic music)

In China, at the beginning of the 21st century,

new clues to the physical appearance of mammals

were unearthed in a deposit dating

from the Cretaceous Period 125 million years ago.

Fossils were discovered in an area

that was once a peninsula with a sub tropical climate.

This world, dominated by huge dinosaurs

like these 30 foot high Titanosaurs,

was also home to mammals

like this Eomaia scansoria,

literally ancient mother that can climb.

Preyed upon by feathered dinosaurs

like this Zhenyuanlong.

Eomaia was the oldest known mammal ancestor

when it was discovered in 2002.

(growling)

(gentle music)

Located in the Liaoning region, northeast of Beijing,

this deposit was once a volcanic area that has preserved

our distant past for millions of years.

(gentle music)

Zhe-Xi Luo, an American paleontologist

of Chinese origin, is at the Seahaytun Cliff

where many long lost fossils have emerged.

- There's this information is lake deposits

and attract all variety of fossil vertebrates,

most famous of all are feathered dinosaurs,

but are very important for understanding

our own human beings early evolutionary history

are the cretaceous mammals.

- [Narrator] 125 million years ago multiple

volcanic eruptions created a series

of sedimentary layers, pockets of red ash

flattened the mammals into the gray mud

like a printing press.

(chirping)

Measuring six inches from nose to tail

and weighing around an ounce Eomaia would have been

fair game for feathered dinosaurs.

(dramatic music)

- The fossil mammals are preserved very well

because they live nearby shallow water lake.

The sediments accumulated very slow and also

there are occasional volcanic eruptions

so the hot volcanic ash helped to trap

the fossil mammals in the sediments

and that is why they are preserved so well.

Therefore, gave us this beautiful fossil to study.

- [Narrator] At the Natural History Museum

in Beijing, Zhe-Xi Luo studies fossils

of the Eomaia Scansoria group, placental mammals

whose fetuses are sustained in the uterus

by a placenta just like humans.

The whole body of the animal is beautifully preserved,

a dream come true for any mammal specialist.

- It is absolutely amazing that we have

the entire fossils here.

With the complete skeleton we can start

to flash out a more interesting picture

about these earliest mammals.

This guys lived in Cretaceous.

It has very grass out jaws and we can recognize

even with naked eye the limbs are quite slender

and we can tell by its very long fingers

and the different nail structures

that they are tree climbers.

It shows that the placental ancestors

are capable of exploring the oboreal or tree living niches

than all these other contemporaries and this gave us

a big evolutionary advantage.

(squeaking)

- [Narrator] Eomaia left its young high up

out of reach of dinosaurs, but sometimes

slept on the ground.

These very first mammals would have to leave

their shelter in order to drink.

(squawking)

(birds chirping)

Their extraordinary mobility is revealed

by the skeleton, particularly by the elongated

trapezoid bones which resemble those

of tree dwelling primates.

- It is really by studying the ankle joint

we are able to recognize great many features

to place this particular fossil on the line

that eventually gave rise to modern placentals.

- [Narrator] Its feeding habits were revealed

thanks to its extremely well preserved teeth.

- You can tell that this mammals have a very sharp cusp

in the front and in the lower teeth generally

there were a series of very sharp triangles

and those are very effective for cutting

the skeletons of insects and also slice off

the flesh out of worms.

(sniffing)

(squeaking)

(chirping)

- [Narrator] After the discovery of Eomaia

more fossils were unearthed in China

changing the vision that paleontologists had

of ancient mammals.

Countless wonders are kept at the Institute

of Vertebrate Paleontology in Beijing.

Among them is a Repenomamus with a complete

and unusually large skeleton.

(dramatic music)

Yuanqing Wang is the paleontologist in charge

of studying this strange 30 inch creature

unearthed in 2004.

- A lot of Mesozoic mammals are

at about the size of moles, a rat.

So, this is quite big.

- [Narrator] Another feature of this large mammal

is its sharp pointed teeth embedded in a strong jaw.

- Before we found this animal we know Mesozoic mammals

usually we saw they were sent to us and small,

a shadow of dinosaurs.

You can see the teeth like sharp and pointed,

so they were carnivore animal, especially

in his stomach area.

There is some fragmentary bones of baby dinosaurs

called stegosaurus.

So we said, okay, this guy ate dinosaurs.

- [Narrator] The animal's stomach contents

are revolutionary.

They contain proof that some mammal ancestors

actually fed on young dinosaurs

rather than living in their shadow.

(snorting and barking)

(growling)

Paleontologists do not know exactly how they hunted.

They believe Repenomamus worked together in packs

like wolves.

(upbeat music)

(growling)

The Beijing collection has many surprises

in store for scientists.

Discovered in 2006, Volaticotherium has

an unusual feature, a large fold of skin

connecting its upper and lower limbs.

(gentle music)

Observed under a microscope this dark stain

reveals the presence of numerous hairs.

Called a patagium, it's a fine membrane of skin

covered in fur.

Like a flying squirrel the taut skin stretched

between its limbs meant that volaticotherium

was able to glide from the trees.

Before this discovery scientists believed

that bats were the first flying mammals to appear

50 million years ago.

Volaticotherium was around the same time

as the dinosaurs showed that flying mammals

were around long before that.

This nocturnal hunter waited for dusk

to start searching for its prey.

(gentle music)

- It's really interesting.

It's taught us the ecological diversity

of the Mesozoic mammals and much wider

than we thought before.

We saw that animals lived in trees or walking on ground.

These animals can glide in the air.

(dramatic music)

- [Narrator] This flying animal confirms

that mammals had adapted to different environments

long before the extinction of dinosaurs.

Despite the discovery of these fossils in China

one question still troubled the scientific community

during the early 21st century.

When did placental mammals first appear?

Geneticists and paleontologists thrashed out

their opposing views in scientific journals.

In the German town of Oldenburg a team of researchers

hunts down the genes of modern mammals

in order to construct their family tree.

- We can estimate by seeing how similar

a gene is in two different species of mammal

how closely related they are.

- [Narrator] Olaf Bininda-Emonds is the author

of a 2007 study which analyzed the genes

of 99% animals living today.

(gentle music)

This mammoth task required eight months

of DNA sequencing to track the genetic mutations

of 60 markers throughout the evolution of mammals.

- The molecular data will give us a much more

complete picture.

We have DNA here from many more species

than we have fossil data for.

The fossils will give us point estimates

throughout the tree.

The DNA will fill in the gaps and give us all

the divirenges times for all the species of mammals

and all the common ancestors that were.

- [Narrator] This method, called the Molecular Clock,

shows that placental mammals separated

from marsupials 160 million years ago

during the Jurassic Period,

then diversified during the Cretaceous Period

to form the current main groups, rodents,

carnivores and primates, an unexpected result,

since no fossil of these early mammals

has ever been discovered.

- This was interesting because there's

a very big disconnect between molecular studies

and fossil studies.

- [Narrator] In Pittsburgh, on the other side

of the Atlantic, another study offered

very different results.

(gentle music)

It is the work of John Wible, a paleontologist

at the Carnegie Museum of Natural History.

Its starting point was the discovery of a skull

found in a 75 million year old deposit in Mongolia

named malestes gobiensis.

It has been studied from every angle

since it does not belong to any known species.

400 of its morphological features

have been compared to those of 82 fossil

or living mammals.

- What we did is we looked at the individual

morphological features of this animal

across a broad array of other fossil forms

and living mammals to try to figure out what it was,

what it was related to and our study supported

the traditional view that there were no fossils

living during the Cretaceous that were members

of the placental group itself.

There were only the ancestors of placentals living.

- [Narrator] Which of these two studies should we believe?

Fossil or genetic?

- The molecular studies all tend to say

that the crown group orders, rodents, primates,

carnivores, bats, they all have the origins

in the Cretaceous when the dinosaurs

were still alive.

The problem is, there's absolutely no fossil

evidence supporting this.

- Many of these modern groups, according

to the Molecular Clock analyses actually are,

they should be present in the Cretaceous record.

We can't find them.

- There's no doubt that there were placental mammals

in the Cretaceous.

What's debated is what kind of placental mammals they are

and it's a question of who's right at the moment.

- [Narrator] To achieve the most complete

mammal family tree both types of data

will need to be refined.

Defining the pace of genetic mutations on one hand

and seeking fossil beds on the other

since new fossils would confirm the geneticists hypothesis.

In the meantime, paleontologists are also trying

to understand how these early mammals

protected themselves from dinosaurs.

The ability to nurse their young

could have been a benefit.

(gentle music)

- If we want to understand how modern theories

come from, we need to look at modern theories'

distant relatives.

Zhangheotherium is a mammal that is even more ancient

than placental mammals.

This extremely well preserved fossil was discovered

in China in 1997.

- We can be relatively sure it is a mammal

because it had fur and associated with fur

would be a whole series of reproductive features

as we know that it must have nursed it fetuses,

but we don't know if the fetuses was born

either in a egg or a live fetus.

- [Narrator] Lactation offers an advantage

when food is scarce since the young

continue to be fed, thanks to their mother's body reserves.

Lactation first appeared in the form

of hundreds of milk producing glands

on the abdomen, just like modern platypuses.

The young would lick the thick milk

from their mother's hair.

(gentle music)

Zhangheotherium has another characteristic

in common with monotremes like the platypus,

a spur on its hind leg.

- This species definitely has another fossil

that has preserved a wishbony spur

and it's also consistent with the first

operative directly from this particular specimen.

In modern monotreme, this spur is definitely used

for self defense, but we do not know

if it is truly poisonous or it's just a bony spur.

- [Narrator] Snakes have fangs.

Insects can sting.

But, this defense technique is rare

among modern mammals.

(gentle music)

(squealing)

(growling)

Located on the male's hind legs,

this spur may have released a venom

capable of paralyzing their foe.

(growling)

According to scientists this weapon is

not terribly efficient, since it takes time

for venom to have an effect.

As they evolved they tried other strategies

like running away and to improve this tactic,

what better than a superior sense of hearing?

The evolution of ear bones was a key advantage

for primitive mammals.

In 2011 the discovery of this veaconodin fossil

shows at last how the jawbones of these reptiles

migrated to form the middle ear of modern mammals

120 million years ago.

- This specimen is a most great mammal

we have ever found in western Liaoning.

All bones are preserved here.

So, it's a very beautiful specimen.

Especially this has preserved some tiny bones

of the ear region.

This here ear is very difficult to be preserved

in fossils because it's very tiny.

More important it is a transitional stage

of the mammalian middle ear evolution.

- [Narrator] In ancient mammals the lower jaw

was linked to the skull by an elongated bone.

The Arctocyonidon this evolved to begin

forming the ear bones.

The hammer, anvil and the tympanic ring

became completely detached in modern mammals

to form the inner ear.

Amazingly, every mammal embryo, including humans,

reproduces this evolutionary phase in the womb

resulting in the formation of the inner ear.

This precision tool allows us to analyze everything

that happens around us constantly.

- Yes, you can hear the dangers earlier

than the other kind of animals.

So, it helps them escape from the predators.

- [Narrator] The mystery of the inner ear bones,

a link with our reptilian past, is cleared up

thanks to this new fossil.

(gentle music)

Another mammal weapon, teeth, reveal their secrets

at the University of Washington in Seattle.

This is where Gregory Wilson uses state of the art

technology to analyze the teeth of the multituberculates,

mammal species that became extinct 34 million years ago.

- We found some really exciting results actually.

What we found is that these multituberculates

that were living alongside dinosaurs

actually undergo an adaptive radiation 20 million years

before dinosaurs go extinct.

And what we see is that they go from having teeth

with a few cusps on them such that they can eat

insects and so on to having teeth that have

many different cusps or tools, such that they can

exploit a new resource in flowering plants.

It's that ability to exploit that new resource

that allows them to expand in terms of numbers

of different species of multituberculates

as well as the range of body sizes that they have

such that they were able to survive

the mass extinction that killed off dinosaurs.

- [Narrator] His study shows that multituberculates

evolved well before the extinction of dinosaurs.

They move from an insect based diet to a diet

based on fruit or even angiosperms, flowering plants

that appeared during the Cretaceous Period.

(gentle music)

To reach this astonishing result Gregory Wilson used

fossils collected over 100 years in Montana's

Hell Creek Formation.

By studying this collection of tiny teeth

under a microscope he was able

to familiarize himself with the many species

of multituberculates.

(gentle music)

- This is the largest of multituberculates that lived,

the size of maybe a beaver or a marmot

and it has many, many bumps all along the tooth row.

Those bumps act as tools to crush and grind food.

Another example sits inside this tiny vial.

It's another multituberculate, but it also

had teeth with many little bumps.

So, this was a smaller version of this animal

that lived during the time of dinosaurs.

This lineage we've known about for a very long time,

but it's been difficult to really quantify it

or understand what the shape of those teeth mean.

We've tried many different approaches,

but none have really been able to give us

the precision that we can now attain today.

- [Narrator] This technological revolution

came in the form of the CT scan, a medical imaging tool

nowadays used by paleontologists.

Specimens like this 67 million year old tooth

are first scanned with x-rays on a microscopic scale.

It is identifiable by its long incisor,

but what intrigues researchers is the complexity

of its molars.

Once the data is collected cartography software

reconstructs an accurate map showing the shape

of the teeth.

Gregory Wilson has found that carnivores

have a fairly simple tooth structure

with approximately 110 cusps per row of teeth,

while multituberculate teeth are far more complex

with up to 348 cusps.

- This particular specimen that I just pulled up

has about 250 different complex little tools

on the surface of its tooth row

and those little tools help break down plant material

that needs to be processed very finely

in order to be digested properly.

So, these guys have evolved towards eating plants.

(chirping)

(gentle music)

- [Narrator] It is this key function of grinding

which promoted the explosion of herbivore

and omnivore species, an ecological niche

untapped by primitive mammals.

Despite these multiple discoveries,

at the end of the 20th century the crucial question

about the origins of the first real mammals remained.

Once again, the Liaoning region provided the answer.

In 2011, Chinese farmers found the fossil

of a mammal called Juramaia sinensis,

meaning Jurassic mother from China.

The paleontologist, Zhe-Xi Lou, has come

for the first time to visit this area

which stretches over several miles.

It is not an easy task to identify

fossil bearing rocks under the fields of lush corn.

But he is guided by a local specialist

and feathered dinosaurs whose oldest specimen,

Anchiornis, was excavated on a site close to this one.

(gentle music)

- It's exciting fossil discovery because it gave us

a new milestone as to when the placental lineage

first started appear on earth and the older

modern placental mammals have a deep root

into the Jurassic and it's coming from right here.

This rocks also are embedded with volcanic ashes

and this sites had been dig by geochronology

to be 160 million, plus or minus a little bit.

So, we know for sure that this rocks

actually belonged to the late Jurassic.

- [Narrator] The Juramaia senensis fossil

is the oldest specimen of a placental mammal

and is a critical piece of the puzzle

in the evolution of mammals, was identified

by its teeth which included molars, canines and incisors.

As the genetic studies of living mammals showed

their origin is much older than existing fossils

that suggested since the discovery of Juramiaia

means the placental mammals must have appeared

at least 35 million years before Eomaia scansoria.

And even though paleontologists are still seeking

fossils from the Cretaceous Period belonging

to current groups like rodents or carnivores,

this discovery brings the conflicting opinion

of geneticists and paleontologists closer together.

- Independent corroboration by fossils on one hand,

and by molecules on the other, gave us

the confidence that we are getting closer

to the correct answer.

- [Narrator] With Juramaia we know

that 160 million years ago mammals already had

the characteristics that made them successful,

fur, complex teeth and acute hearing

to escape predators and locate their prey.

- The general adaptation such as insect worry

and such as capability to move on the tree

gave this particular mammal some evolutionary advantage.

It is really equipped well enough already

in the late Jurassic for its descendant to thrive

after the dinosaurs' extinction.

(dramatic music)

(growling)

- [Narrator] Certainly the mammals ancestors

were very small at the time of dinosaurs,

but much more varied and better equipped

than was previously thought

with advantages that we find later in primates,

our closest relatives.

(growling)

(dramatic music)