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Hi, I'm Dr. Lesley Williams,
and I'd like to welcome you
to Biology of Marine Mammals.
In this course, we use the study
of marine mammals as framework
to explore major biological
principles that actually apply
to all living organisms.
Now, the study of biology
is extremely diverse,
ranging from the study
of macromolecules
and how they move inside
our tiny, tiny cells,
all the way to the study
of whole communities
and ecosystems, such
as those found
in Yellowstone National
Park, but here we will focus
on mammals, and more
specifically marine mammals,
as a template for studying some
of these major biological
principles.
After a proper introduction
to marine mammals,
we'll then spend the first
third of the course learning
about the theories of natural
selection and evolution,
and how to apply
these principles,
as we explore marine mammal
evolution and diversity.
Next, we move on to the
fascinating branch of anatomy
and physiology, which
is actually the study
of body form and function.
Here we'll explore the body
structure and function of whales
and dolphins, seals and sea
lions, and even the sea otters,
to demonstrate how a marine
mammal's body has adapted
to live in these
marine environments.
Of course, all organisms
interact with their environments
so we will study
the interactions
between selected marine mammals,
such as northern elephant seals
and sea otters, and
their environments
to explore biological topics,
such as ecology, behavior,
and even human conservation.
It is my hope that through the
study of these mysterious, yet,
awe-inspiring marine mammals,
you will have advanced
your general understanding
of the processes that govern
all living organisms, thus,
enhancing your role as
an educated citizen.
So, without further ado,
let's begin our first lecture,
which simply addresses
this question:
What are marine mammals?
Okay, in order to address:
"What are marine mammals?"
we first need to actually take
a look at animals in general;
and then talk about which
properties define mammals;
and from there, we'll
take a look
at what defines a marine mammal.
Let's get started.
Alright, let's start
with the animals.
When we think of
animals, it's convenient
to actually break them
down into two basic groups:
we'll say the invertebrates--
which include animals,
such as worms and insects, and
even things like sea urchins
and sea stars-- and then
we have the vertebrates.
Now, to be called a vertebrate,
you have to actually satisfy two
criteria: one is the presence
of a cranial case-- so,
when we have a cranial case,
that simply means you have a
skull, or something like that,
that protects a brain;
and then the other one,
which is more commonly
known, is that you have
to have a backbone, so
some type of rigid bone
that basically goes
through your back.
It's not always made of bone,
but something like that,
that gives you support
for your back.
So, vertebrates, themselves,
are a very, very diverse group,
and we go from fish to
amphibians, to reptiles, birds,
and, of course, mammals.
So, mammals are included in
the study of vertebrates.
So, let's take a look
at: What are mammals?
So, when we think of all the
different mammals, mammals tend
to share these characteristics.
Now, it's important
to understand
that I'm saying, "share."
It doesn't mean that they're
defined by these characteristics
or that other animals lack
some of these, but rather,
when we look at all
the mammals as a whole,
we tend to see these trends.
First, that they tend
to give live birth.
There are actually two
exceptions to this--
one being the duck-billed
platypus--
but as a general rule, they
give live birth, and of course,
humans, being mammals,
we recognize this.
When we give birth, we give
birth to a living baby.
We don't, let's say, lay an egg.
So, that's what's meant
by giving live birth.
Another is that parental
care tends to be extensive,
and of course there is no
more extensive parental care
than when we look at humans,
which of course are mammals;
that is: we raise our young for
an extended period of time--
feeding them, nourishing them,
providing behavioral guidance--
and so, of course, for humans we
see that is marked extensively,
but if we compare that to
other animals, like insects,
they simply lay their eggs,
and most of the time the parents
leave and the newborns are left
to fend for themselves.
So, that is a feature
of being a mammal,
and of course mammals
are classified
as being warm-blooded; now,
that actually takes a
little bit of explanation.
What does being warm-blooded
mean?
Well, yes, your blood is warm,
but more specifically it means
that you use metabolism
to generate your own heat.
You are not strictly relying on
the environment to warm you up.
That's in sharp contrast
to many reptiles
that are considered
to be cold-blooded.
They often will try to go to
a warm area, sun themselves,
for example, so that they
get the infrared radiation
from the sun to help
warm up their bodies.
We, as mammals, don't need that.
We tend to maintain a pretty
consistent temperature simply
by using the energy we generate
from metabolism and movement,
so that makes us warm-blooded;
and finally, mammals, of course,
tend to be intelligent.
So, now that we've talked about
some of the characteristics
that mammals share, let's
actually define them.
All mammals are differentiated
from other vertebrates
by two major properties: one
is the presence of hair--
and of course, simply go to
your own body and you will know
that you have hair
on your body so,
of course, mammals have hair.
Humans tend to have less
hair than many other mammals,
such as dogs and cats,
and many marine mammals,
such as whales and dolphins.
You may think: "Uh, I've
never seen a hair on them,"
but they actually do have them,
although there're not very many.
So, all marine mammals
have hair,
even if it's just a few sprouts
of it, and then, of course,
all marine mammals have-- or
at least all the females do--
have mammary glands that
produce milk for their young.
So, those are two properties
that actually define
being a mammal.
Alright, so now,
let's take a look at:
Who are our marine mammals?
When you tend to think in your
head about marine mammals,
you probably think of whales
and dolphins and seals
and sea lions, and
maybe even sea otters.
Those might be what you
call "the usual suspects,"
and what I mean by that are
gonna be mammals that live
in the marine environment, and
you recognize them as, hey,
these are mammals that
live in the ocean,
to be marine means
to be oceanic.
So, these are mammals that
we find in the ocean--
whales, dolphins, seals,
sea lions, even sea otters--
but that's not the best
definition of marine mammals
from a biological standpoint
because there are
actually some exceptions,
or oddities, to that rule.
So, yes, marine mammals are
going to be mammals that live
in the sea, but we're gonna
include a few extras in there,
as well, such as river dolphins;
we have land-locked seals--
so, these are seals that are
actually found in big lakes.
They're not found in the
ocean-- and then the polar bear.
So, I'm gonna briefly tell
you about why each one
of those groups is still
encompassed in marine mammals.
So, when we take a look at the
river dolphins, it turns out,
yes, the river dolphins don't
live in the ocean, per se,
they live in rivers, which
tend to be more freshwater,
but the river dolphins
are evolutionarily related
to all the other
marine dolphins.
So, rather than say their
own branch of science,
we just group them
in and say: "Yes,
they live in the
river, but it's okay.
We'll still include them in
the study of marine mammals
because of their
evolutionary relationship
to all the other dolphins, and
that also applies to any seals
that are considered
to be land-locked."
In other words, they
live in a lake
and they can't get to the ocean.
Because they evolved
from oceanic seals,
we still include
them in our study.
Now, the polar bears
are really interesting
because the polar bears actually
spend quite a bit of their time
on land or even on sea ice.
In fact, I wouldn't say
they spend the majority
of their time in water.
In fact, they're rather poor
swimmers and can actually drown
in the marine environment.
So, why on earth
do we study them
as we study marine mammals?--
and the technicality
lies in the fact
that polar bears spend a lot of
their time, or can spend a lot
of their time, on sea ice,
which essentially is ice
that has frozen from the sea.
So, when we look at sea ice,
we still consider it to be part
of the marine environment.
So, for that reason, polar
bears are also included
in the study of marine mammals.
And so now that you have a
flavor for what defines mammals,
what defines marine mammals,
we are ready to get started
with this class, and I
will see you next time.
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