Ancient Earth (2017) - full transcript
In this 3-part original and exclusive CuriosityStream series, travel back in time to visit the three most powerful extinction events in Earth's history. Only in the last blink of an eye have a variety of ancient sea creatures and land dwellers evolved to inhabit the Earth. This series explores the major events that wiped out between 70-90% of Earth's species developed during the Permian, Triassic and Cretaceous periods. Available in 4K only on CuriosityStream.
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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.
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 devour
young, feathered dinosaurs.
They must have been
victim to large predators,
like these yutyrannuses.
They are much bigger than
all previously known mammals.
These repenomamus
lived 130 million years ago
in a highly active volcanic area.
Preserved in fine, volcanic ash,
their skeletons have survived the ages,
radically changing
paleontologist's understanding
of the first mammals.
These fossil mammals
are certainly related to
our own evolutionary history in the sense
that we, ourselves, are mammals.
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.
And 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.
The fossils discovered
at the beginning of the 21st century
show that the first modern mammals appeared
125 million years ago, but
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
were mammalian reptiles,
like these thrinaxodon, a
relative of the reptile family.
Thrinaxodon 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.
Using this innovation, Vincent
Fernandez is able to study
the contents of the
rock without destroying it.
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.
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.
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.
A hundred 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.
This high resolution technology
revealed the presence
of a thrinaxodon, a long
lost mammal ancestor,
plus, an unexpected bonus,
an amphibian named
broomistega, lying by its side.
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.
Just as some mammals hibernate
to protect themselves from the cold,
this thrinaxodon burrows underground,
and estivates to avoid the heat.
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.
We discovered that the
broomstega was wounded.
It had a series of seven
broken ribs that were healing.
We knew that because
it has small bone growth
around the fractures, so
we see the healing process.
We know it was probably
injured for several weeks.
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.
The lineage to which thrinaxodon 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.
Vincent and his South African colleagues
are now searching for new burrows to scan,
hoping to solve other mysteries.
We are also looking for an egg,
or a pregnant female
that will finally tell us
which mode of reproduction
our ancestors had.
It's a difficult task,
because mammal fossils
from the Triassic period
are very rare.
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 Gheerbrant
remembers his early
years as a paleontologist.
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.
These tiny fragments
are obtained through painstaking work.
Paleontologists must sieve
several tons of sediment
to uncover just a few of
these mammalian teeth.
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.
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.
That's exactly what the collection
studied by Emmanuel
Gheerbrant's team looks like.
Started in 1976 in a
fossil deposit near Narcy,
in Northeastern France, it now contains
close to a thousand teeth
from the Upper 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 animals species
have only one type of tooth.
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.
Though they tell us more
about how these dinosaur age mammals ate,
they fossils give no indication
as to what they looked like.
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 Archingeay 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 Romain Vullo and Didier Néraudeau.
Look at this.
This leaf has been in clay
for the past hundred million years.
Comes off, and if I blow on it,
I can bend it, which
shows that it's still flexible.
Apart from its change in 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.
So, here we are at the
bottom of the quarry.
Water has poured down
and created an interesting little outcrop,
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 contain plant debris,
and small pieces of amber,
which is what we're
looking for in particular.
The sediment is then
sieved in a nearby pond.
We've got quite a few small fragments here.
That's a good sized piece.
It's slightly translucent,
part brown, part red.
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 Vullo's colleagues
made an exceptional discovery.
Two hairs, trapped in amber.
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 presents
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.
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 decimated large dinosaurs.
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 hight titanosaurs
was also home to mammals.
Like this Eomaia scansoria, literally,
ancient mother that can climb.
Preyed upon by feathered
dinosaurs like Zhenyuanlong,
Eomaia was the oldest known mammal ancestor
when it was discovered in 2002.
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.
Zhe-Xi Luo, an American paleontologist
of Chinese origin is at the Xihatun Cliff
where many long lost fossils have emerged.
This Ni Tian formation is lake deposits
and it trapped 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 these Cretaceous mammals.
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.
Measuring six inches from nose to tail,
and weighing around an ounce,
Eomaia would've been fair
game for the feathered dinosaurs.
The fossil mammals are preserved very well
because they lived
nearby shallow water lake.
The sediments cumulated fairly slow,
and also there are
occasional volcanic eruptions,
so the hot volcanic ash helped to trap
those fossil mammals in the sediment,
and that is why they are preserved so well.
Therefore, gave us this
beautiful fossil to study.
At the Natural History Museum of 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 entire skeleton
we can start to flush out
a more interesting picture
about these early mammals.
These guys lived in Cretaceous,
it has very grassile jaws,
and we can recognize
even with the 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.
This shows that the placental ancestors
are capable of exploring the arboreal,
or tree-living niches than all
these other contemporaries,
and this gave us a big
evolutionary advantage.
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.
Their extraordinary mobility
is revealed by this 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
a great many features
to place this particular fossil on the line
that eventually gave
rise to modern placentas.
Its feeding habits were revealed
thanks to its extremely
well-preserved teeth.
And you can tell that these mammals have
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.
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.
Yuanqing Wang is the paleontologist
in charge of studying
this strange, 30" creature,
unearthed in 2004.
A lot of Mesozoic
mammals that are about the
size of a mouse or rat.
So, this is quite big.
Another feature of this large mammal
is its sharp, pointed teeth,
embedded in a strong jaw.
Before we found this animal,
we know with Mesozoic
mammals, generally it was thought
they're insectivores, and small,
living in the shadow of the dinosaurs.
You can see the teeth,
they're sharp, and pointed.
So, it's a carnivorous animal.
Especially in his stomach
area there are some
fragmentary bones of baby
dinosaurs called Psittacosaurus,
so we said, "Okay, this guy ate dinosaurs."
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.
Paleontologists do not
know exactly how they hunted,
but they believe repenomamus
worked together in packs
like wolves.
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.
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, who 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.
It's really interesting, it's told us that
ecological diversity of
the Mesozoic mammals
is much wider than we thought for,
really with other animals,
it was living in the tree,
or walking on the ground.
Like these animals can climb there.
This flying animal confirms
that mammals had adapted
to different environments
long before the
extinction of the 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.
Olaf Bininda-Emonds is the author
of a 2007 study which analyzed the genes
of 99% of animals living today.
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 for 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 divergence times
for all the species of mammals
and all the common ancestors that were.
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.
In Pittsburgh,
on the other side of the Atlantic,
another study offered
very different results.
It is the work of John Wible,
a paleontologist at the Carnegie
Museum of Natural History.
It's starting point was
the discovery of a skull
found in a 75 million year
old deposit in Mongolia
named Maelestes 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 the placentals living.
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 their origins
in the Cretaceous when
the dinosaurs were still alive.
The problem is there is
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.
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.
If we want to understand
how mon eutherians come from
we need to look at mon
eutherians' 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 its fetuses
but we don't know if the fetuses was born
either in a egg or a live fetus.
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.
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 with a bony spur,
and it's also consistent
with the first observation
directly from this particular specimen.
In modern monotremes,
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.
Snakes have fangs, insects can sting,
but this defense technique is
rare among modern mammals.
Located on the male's hind legs
this spur may have released a venom
capable of paralyzing their foes.
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 Liaoconodon 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's the most complete mammal
we have ever found in Western Liaoning.
All the bones are preserved here,
so it's a very beautiful specimen.
Especially this specimen preserves
the tiny bones of the ear region.
These ear ossicles
usually 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.
In ancient mammals the lower jaw
was linked to the skull
by an elongated bone.
In Liaoconodon this evolved
to begin forming the earbones.
The hammer, anvil, and 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, it can hear the
dangers earlier than the
other kind of animals, so, helps them to
escape from the predate.
The mystery of the inner ear bones,
a link with our reptilian past,
is cleared up thanks to this new fossil.
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 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.
This study shows that multituberculates
evolved well before the
extinction of dinosaurs.
They moved from an insect based diet
to a diet based on fruit,
or even angiosperms,
flowering plants that appeared
during the Cretaceous period.
To reach this astonishing result,
Gregory Wilson used fossils
collected over a hundred 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.
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
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.
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 multitubercular
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.
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 Luo
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
in feathered dinosaurs whose
oldest specimen, Anchiornis,
was excavated on a site close to this one.
It's exciting fossil discovery because
it gave us a new milestone as to when
the placental lineage first
start to appear on Earth,
and all the modern placental
mammals have a deep root
into the Jurassic and it's
coming from right here.
These rocks also are
embedded with volcanic ashes
and this site had been
dated by geochronology
to be 160 million,
plus or minus a little bit,
so we know for sure these rocks
actually belong to the late Jurassic.
The Juramaia sinensis 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
had suggested since
the discovery of Juramaia
means that 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.
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 insectivory,
and such as capability to move on the tree,
gave this particular mammal
some evolutionary advantage.
It has really equipped
it well enough already
in the late Jurrasic for
it's descendant to thrive
after the dinosaurs extinction.
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.
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.
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 devour
young, feathered dinosaurs.
They must have been
victim to large predators,
like these yutyrannuses.
They are much bigger than
all previously known mammals.
These repenomamus
lived 130 million years ago
in a highly active volcanic area.
Preserved in fine, volcanic ash,
their skeletons have survived the ages,
radically changing
paleontologist's understanding
of the first mammals.
These fossil mammals
are certainly related to
our own evolutionary history in the sense
that we, ourselves, are mammals.
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.
And 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.
The fossils discovered
at the beginning of the 21st century
show that the first modern mammals appeared
125 million years ago, but
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
were mammalian reptiles,
like these thrinaxodon, a
relative of the reptile family.
Thrinaxodon 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.
Using this innovation, Vincent
Fernandez is able to study
the contents of the
rock without destroying it.
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.
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.
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.
A hundred 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.
This high resolution technology
revealed the presence
of a thrinaxodon, a long
lost mammal ancestor,
plus, an unexpected bonus,
an amphibian named
broomistega, lying by its side.
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.
Just as some mammals hibernate
to protect themselves from the cold,
this thrinaxodon burrows underground,
and estivates to avoid the heat.
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.
We discovered that the
broomstega was wounded.
It had a series of seven
broken ribs that were healing.
We knew that because
it has small bone growth
around the fractures, so
we see the healing process.
We know it was probably
injured for several weeks.
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.
The lineage to which thrinaxodon 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.
Vincent and his South African colleagues
are now searching for new burrows to scan,
hoping to solve other mysteries.
We are also looking for an egg,
or a pregnant female
that will finally tell us
which mode of reproduction
our ancestors had.
It's a difficult task,
because mammal fossils
from the Triassic period
are very rare.
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 Gheerbrant
remembers his early
years as a paleontologist.
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.
These tiny fragments
are obtained through painstaking work.
Paleontologists must sieve
several tons of sediment
to uncover just a few of
these mammalian teeth.
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.
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.
That's exactly what the collection
studied by Emmanuel
Gheerbrant's team looks like.
Started in 1976 in a
fossil deposit near Narcy,
in Northeastern France, it now contains
close to a thousand teeth
from the Upper 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 animals species
have only one type of tooth.
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.
Though they tell us more
about how these dinosaur age mammals ate,
they fossils give no indication
as to what they looked like.
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 Archingeay 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 Romain Vullo and Didier Néraudeau.
Look at this.
This leaf has been in clay
for the past hundred million years.
Comes off, and if I blow on it,
I can bend it, which
shows that it's still flexible.
Apart from its change in 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.
So, here we are at the
bottom of the quarry.
Water has poured down
and created an interesting little outcrop,
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 contain plant debris,
and small pieces of amber,
which is what we're
looking for in particular.
The sediment is then
sieved in a nearby pond.
We've got quite a few small fragments here.
That's a good sized piece.
It's slightly translucent,
part brown, part red.
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 Vullo's colleagues
made an exceptional discovery.
Two hairs, trapped in amber.
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 presents
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.
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 decimated large dinosaurs.
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 hight titanosaurs
was also home to mammals.
Like this Eomaia scansoria, literally,
ancient mother that can climb.
Preyed upon by feathered
dinosaurs like Zhenyuanlong,
Eomaia was the oldest known mammal ancestor
when it was discovered in 2002.
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.
Zhe-Xi Luo, an American paleontologist
of Chinese origin is at the Xihatun Cliff
where many long lost fossils have emerged.
This Ni Tian formation is lake deposits
and it trapped 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 these Cretaceous mammals.
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.
Measuring six inches from nose to tail,
and weighing around an ounce,
Eomaia would've been fair
game for the feathered dinosaurs.
The fossil mammals are preserved very well
because they lived
nearby shallow water lake.
The sediments cumulated fairly slow,
and also there are
occasional volcanic eruptions,
so the hot volcanic ash helped to trap
those fossil mammals in the sediment,
and that is why they are preserved so well.
Therefore, gave us this
beautiful fossil to study.
At the Natural History Museum of 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 entire skeleton
we can start to flush out
a more interesting picture
about these early mammals.
These guys lived in Cretaceous,
it has very grassile jaws,
and we can recognize
even with the 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.
This shows that the placental ancestors
are capable of exploring the arboreal,
or tree-living niches than all
these other contemporaries,
and this gave us a big
evolutionary advantage.
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.
Their extraordinary mobility
is revealed by this 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
a great many features
to place this particular fossil on the line
that eventually gave
rise to modern placentas.
Its feeding habits were revealed
thanks to its extremely
well-preserved teeth.
And you can tell that these mammals have
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.
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.
Yuanqing Wang is the paleontologist
in charge of studying
this strange, 30" creature,
unearthed in 2004.
A lot of Mesozoic
mammals that are about the
size of a mouse or rat.
So, this is quite big.
Another feature of this large mammal
is its sharp, pointed teeth,
embedded in a strong jaw.
Before we found this animal,
we know with Mesozoic
mammals, generally it was thought
they're insectivores, and small,
living in the shadow of the dinosaurs.
You can see the teeth,
they're sharp, and pointed.
So, it's a carnivorous animal.
Especially in his stomach
area there are some
fragmentary bones of baby
dinosaurs called Psittacosaurus,
so we said, "Okay, this guy ate dinosaurs."
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.
Paleontologists do not
know exactly how they hunted,
but they believe repenomamus
worked together in packs
like wolves.
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.
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, who 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.
It's really interesting, it's told us that
ecological diversity of
the Mesozoic mammals
is much wider than we thought for,
really with other animals,
it was living in the tree,
or walking on the ground.
Like these animals can climb there.
This flying animal confirms
that mammals had adapted
to different environments
long before the
extinction of the 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.
Olaf Bininda-Emonds is the author
of a 2007 study which analyzed the genes
of 99% of animals living today.
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 for 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 divergence times
for all the species of mammals
and all the common ancestors that were.
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.
In Pittsburgh,
on the other side of the Atlantic,
another study offered
very different results.
It is the work of John Wible,
a paleontologist at the Carnegie
Museum of Natural History.
It's starting point was
the discovery of a skull
found in a 75 million year
old deposit in Mongolia
named Maelestes 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 the placentals living.
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 their origins
in the Cretaceous when
the dinosaurs were still alive.
The problem is there is
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.
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.
If we want to understand
how mon eutherians come from
we need to look at mon
eutherians' 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 its fetuses
but we don't know if the fetuses was born
either in a egg or a live fetus.
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.
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 with a bony spur,
and it's also consistent
with the first observation
directly from this particular specimen.
In modern monotremes,
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.
Snakes have fangs, insects can sting,
but this defense technique is
rare among modern mammals.
Located on the male's hind legs
this spur may have released a venom
capable of paralyzing their foes.
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 Liaoconodon 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's the most complete mammal
we have ever found in Western Liaoning.
All the bones are preserved here,
so it's a very beautiful specimen.
Especially this specimen preserves
the tiny bones of the ear region.
These ear ossicles
usually 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.
In ancient mammals the lower jaw
was linked to the skull
by an elongated bone.
In Liaoconodon this evolved
to begin forming the earbones.
The hammer, anvil, and 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, it can hear the
dangers earlier than the
other kind of animals, so, helps them to
escape from the predate.
The mystery of the inner ear bones,
a link with our reptilian past,
is cleared up thanks to this new fossil.
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 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.
This study shows that multituberculates
evolved well before the
extinction of dinosaurs.
They moved from an insect based diet
to a diet based on fruit,
or even angiosperms,
flowering plants that appeared
during the Cretaceous period.
To reach this astonishing result,
Gregory Wilson used fossils
collected over a hundred 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.
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
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.
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 multitubercular
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.
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 Luo
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
in feathered dinosaurs whose
oldest specimen, Anchiornis,
was excavated on a site close to this one.
It's exciting fossil discovery because
it gave us a new milestone as to when
the placental lineage first
start to appear on Earth,
and all the modern placental
mammals have a deep root
into the Jurassic and it's
coming from right here.
These rocks also are
embedded with volcanic ashes
and this site had been
dated by geochronology
to be 160 million,
plus or minus a little bit,
so we know for sure these rocks
actually belong to the late Jurassic.
The Juramaia sinensis 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
had suggested since
the discovery of Juramaia
means that 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.
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 insectivory,
and such as capability to move on the tree,
gave this particular mammal
some evolutionary advantage.
It has really equipped
it well enough already
in the late Jurrasic for
it's descendant to thrive
after the dinosaurs extinction.
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.