(water splashing)
- I wanna take you back to
a time when whales walked.
It was the beginning of the Eocene
around 50 million years ago.
At the time there were high
temperatures and warm oceans
which created a moist, balmy environment.
There were forests across
the Earth from pole to pole
and continents were on the move,
which changed current systems
so that strong coastal upwellings
drove a surge of nutrients
into upper surface waters.
Diatoms, single-celled algae
bloomed in coastal waters.
So that these warm Eocene
oceans teemed with fish
and other marine life.
It was an ideal place
to hunt for predators
and it was at this time
that the first mammals,
the ancestors of whales
returned to the sea.
Whales didn't evolve as a straight line
from their land mammal ancestor
to these fully aquatic
mammals that we know today.
There were many different amphibious
or semi-aquatic types of
whales that walked on land,
swam in rivers, swum in
coastal waters and oceans.
These different forms
arose really quickly.
Well, quickly in evolutionary times.
Some whale types were more
successful than others.
While most disappeared
some became the ancestors
of whales we know today, so
let's take a closer look.
Our story starts in what
we know as Pakistan.
It was around 50 million years ago
that the early known
cetaceans, the Pakicetus
lived in rivers in Eocene forests.
They looked nothing like we
think of as a whale today.
They were more like a wolf,
but they had whale ears,
auditory bulla, so they were
adapted to hear underwater.
And they had sharp teeth with high cusps
suggesting they ate fish.
So perhaps they swam in rivers,
hauling out to sleep on the
shore similar to a tapir today.
A little later around 47 million years ago
we find Ambulocetus.
It was an ancient whale
that was more adapted
to living in the water than Pakicetus.
They were much bigger than Pakicetus,
more than twice their size, a
little over four meters long.
They were probably still amphibious,
but spent more time in the water.
And their short legs had dense bones
and their strong hind limbs had huge feet
allowing them to be good swimmers,
but clumsy and slow on land.
So Ambulocetus was more like a crocodile
than the wolf-like Pakicetus.
But just like Pakicetus,
they had whale ears,
those heavy, dense boned auditory bulla.
But now they had another whale-like
underwater hearing adaptation.
They had a lower jaw with a large cavity,
which in toothed whales
today is filled with fat.
And this helps sound
transmit from the water
straight back to their ears.
So Ambulocetus, this ancient whale
had taken steps further toward
living an aquatic lifestyle.
Later around 37 million
years ago Durudon appears.
But Durudon was one of the
first of the ancient whales
to give up on land completely.
They moved solely by
tail-powered swimming,
but unlike a shark or fish, they moved
with their enormous tail up and down
just like modern whales
and dolphins do today.
Their hind limbs were tiny, and the elbows
of their forelimbs stiffened
as they became flippers,
ideal for maneuvering and stabilizing
that five-meter long streamlined
body through the water.
Their nostrils are not
at the tip of the snout
as in typical mammals,
but had moved midway
onto the top of their head.
This makes it easier to
catch a breath of air
while underwater.
Around about the same
time Llanocetus appears.
They're one of the first baleen whales,
but they look more like Durudon
than modern baleen whales.
In fact, all these early baleen whales
didn't even have baleen.
Instead they had lobed teeth
that they used to filter feed
just like a crabeater or
leopard seals do today.
Just a little after this at
around 34 million years ago
the Earth's oceans changed.
South America finally
split from Antarctica
so that circumpolar currents spiraled
to isolate the Antarctic continent
and the Earth and her oceans cooled.
Global extinctions soared,
but in those now cold,
nutrient-rich waters around
Antarctica life exploded,
particularly a diverse
array of phytoplankton.
This bonanza of tiny marine plants
sustained huge swarms
of small marine animals
like krill, salps, tiny fish, and squid.
Now enters the time of the
enormous baleen whales.
The baleen whales we know today.
(water splashing on shore)
