Hello marine biology students.
In this last video of the week we're going
to be talking about cetaceans, which include
whales and dolphins.
[Intro Music]
Order Cetacea includes whales, dolphins, and
porpoises.
Their forelimbs are modified into flippers
and they have a fin-like tail called a fluke.
Their nostrils are located on the top of their
head as a single or double opening called
a blowhole.
Among the two suborders of the cetaceans,
are the Mysticeti or the baleen whales and
the tooth dwells which are from the suborder
of Otodontoceti.
Whales may be identified from their fluke
shape, their blow pattern, or the view of
their back when starting a dive.
Baleen whales have rows of flexible fibrous
plates known as baleen that hang from their
upper jaws.
This baleen is made out of keratin, which
is the same material that fingernails and
hair are made of.
They are filter feeders, where they take in
huge mouthfuls of water containing krill or
small fish and the baleen traps the prey as
the water is forced back out of the mouth.
There are 13 species of baleen whales, including
right whales, gray whales, blue whales, and
humpback whales.
Here we can see what these baleen plates look
like in the shape of the mouth cavity for
these whales.
Here we can see a variety of baleen whales.
These are among the largest animals that have
ever lived on the planet Earth.
The toothed whales have simple peg like teeth,
which vary considerably in number and size
among the various species.
Dolphin teeth are conical and interlocking,
whereas those of porpoises are spade-shaped
teeth.
They are adapted for grasping and tearing,
not for chewing.
The diet of toothed whales include fish, squids,
and bottom invertebrates.
The toothed whales include dolphins, porpoises,
belugas, narwhals, sperm whales, orcas, river
dolphins, and beaked whales.
Many are threatened with extinction as a result
of whaling.
Cetaceans are marine mammals, and so they
must breathe air and they have lungs.
They also require some special adaptations
in order to dive for the distances that they
do.
One of these adaptations is rapid breathing
prior to the dive, known as apnuestic breathing.
Their gas exchange is much more efficient
than ours, with their lungs removing about
90% of the oxygen from the air they breathe
in as opposed to only 20% for humans.
They have elastic tissue in their lungs which
helps to temporarily expand the lungs during
apneustic breathing.
Marine mammals have more blood than non-diving
mammals for their size and so this larger
amount of blood includes more hemoglobin for
storing oxygen.
The muscles of a diving marine mammal also
contain more myoglobin
to hold oxygen in the tissues.
Other adaptations for diving include the heart
rate dramatically slowing during a dive known
as bradycardia, blood flow reduced to the
extremities
and the digestive system, making sure that
the central nervous system remains fully oxygenated.
The muscles of diving mammals also employ
anaerobic respiration
as necessary, which results in the build-up
of lactic acid in their muscles to a higher
degree than most other mammals could tolerate.
During a dive, the ribcage and lungs can almost
fully collapse to force air into tissues,
and prevent decompression sickness or the
bends.
An important ability of many toothed whales
is echolocation.
Sound waves are emitted 
as a series of clicks of varying frequencies.
The melon, which is a filled section at the
front of the skull, directs the outgoing sound
waves.
After the sound strikes an object, the echo
is reflected back.
These reflected echoes are then received back
by the melon and the lower jaw itself.
These sound waves are then directed to the
inner ear.
The longer it takes an echo to return, the
farther away the object is located.
This is a characteristic of toothed whales.
Marine mammals have a variety of behaviors.
They are well known for their vocalizations,
including the barking of sea lions and the
songs of the humpback whales.
They engage in play behavior regularly, including
sexual play.
Marine mammals have large brains and have
a great ability for learning new behaviors.
One behavior of many cetaceans is breaching.
Breaching is when a whale or dolphin jumps
out of the water and crashes back into the
water on their back.
The reason for this behavior could be removing
parasites, could be a warning signal, could
be to avoid suitors, or it could just be fun.
Some whales also show spying behavior 
in which they will peek their head above water,
looking to see what's around.
Many whales are known for their long distance
migrations, where their migrations are timed
with feeding in cold water and breeding in
warm water.
When one member of a group or pod is sick,
the other members will care for it.
This occasionally is the cause of mass strandings
where the leader of a pod is sick or injured
and ends up drawing the rest of the pod to
shore.
Another feature of most marine mammals is
maternal care of the young.
When discussing marine mammal reproduction,
fertilization is always internal and so copulation
is involved.
For most cetaceans, the penis remains within
the body before copulation.
Copulation occurs on land for most pinnipeds,
with the exception of the walruses.
Other marine mammals copulate at sea.
As mentioned previously, both in captivity
and in the wild, sexual play is common for
marine mammals.
Another feature of many marine mammals is
delayed implantation
of the fetus, that allows the newborn to be
born at a time that is best for its survival.
So implantation does not occur until the gestation
period would result in a good time for the
offspring to be born.
There are several methods for copulation among
the cetaceans.
Occasionally gray whales need a help from
a buddy, whereas humpback whales mostly have
it figured out on their own.
Gestation time varies in marine mammals, but
it's normally from 11 to 12 months in cetaceans.
Calves are always born tail first so that
they can remain attached to the placenta
until the entire body is out of the mother
and the young can be assisted to the water
surface in order to breathe.
As with previous chapters, there are very
helpful tables at the end of the chapter highlighting
the similarities and differences between these
different marine vertebrates that aren't the
fish, and I'd highly encourage you to go to
Table 9.3 in your textbook to review the information
about these different animal groups.
And that concludes our discussion of cetaceans.
Now, this is the last video before assessment
two and after assessment two we'll start talking
about marine environments and ecosystems.
Alright, I'll see you in the next videos.
Bye.
