Skulls - Marine Mammals
Grade: 3
Overview:
In pairs, students make observations of
mammal skulls and then share their
observations with the larger group. Everyone
then compares the features of the different
skulls trying to determine how each feature
might help the different mammals survive in the
marine environment.
Materials:
Harbor seal skull
Dolphin skull
Sea Otter skull
California sea lion skull
Picture of living animal for each
skull-with name printed on it.
Raccoon skull
Elephant seal skull
Baleen
Word cards for parts of the skull
Key Concepts/Learning Objectives:
Marine mammals have skull features that are
different from land mammals that help adapt
the marine mammals for surviving in the ocean.
Focus Questions:
What can we learn about a
mammal’s lifestyle by studying
its skull?
Prep/Set up:
Hide the names of animals on the skulls with
blue tape and also on the pictures.
Timing/Flow:
7 minutes - examine and
identify 1 skull
5-8 minutes - compare features
between skulls
3 minutes - apply knowledge to
new skull
Clean up:
Carefully place each skull back in the packing
materials.
Other Kits in this programs:
Bird adaptations
Camouflage/Warning colors
Kelp
Stewardship message:
A healthy ecosystem has a wide variety of
living organisms within it. All play
important roles within their environment
using specific adaptations which help
them to survive and reproduce.
Opening
Timing: 1 minute
Introduce yourself and ask the students to introduce themselves.
Activity: Skills: Observe, explain
Timing: 5 minutes
Explain to the students we are going to do an activity using replicas of marine mammal skulls. Ask
students to share ideas of how they should handle the skulls. Responses may include:
• Treat them gently
• Open and close mouth slowly with care, etc.
Pair up students and give each one a skull to examine – do not tell them which animal they have yet:
• CA Sea Lion
• Harbor Seal (note with a smaller group, this may be the one you leave out.)
• Sea Otter
• Dolphin
Ask students to talk to their partner and identify features that they find interesting, or perhaps features
that make them wonder “what is this for?” They can even make guesses about what features are for.
They should listen to their partner’s ideas and then they will share with the group.
Give students about 2 minutes to observe and share ideas. Then call on each group to share their
skull observations.
Sample Conversation:
Teaching tips:
Activity: Skills: Match & explain
Timing: 2 minutes
First see if any of the groups think they know which animal they have. If they have a guess,
regardless if they are right, be sure to ask them to give reasons for their answer.
Show the pictures of the live animals and have the students match their skull to the pictures. Be sure
to have students provide reasons for their answers.
Activity - Skill: Compare/Contrast
Timing: 3 minutes
Put all of the skulls in the center of the table so students can see them with the accompanying
picture.
Use the observations from the first activity as a starting point to explore the various features of these
skulls.
Teeth:
Ask students if they know what each of these animals eats. Notice that they are all meet eaters.
Now compare the teeth. Notice there are a lot of differences.
Read the following statements and have students consider which of the animals it is for. Be sure
students give reasons for their answer.
• This animal catches slippery fish and swallows them whole. (dolphin)
•
•
This animal swallows its food whole, or tears it into pieces but doesn’t chew. It may use its
back teeth to crush shells. (CA sea lion and harbor seal)
This animal uses rocks to crush the shells of its prey. It can use its back teeth for chewing its
food. (Sea otter)
If the students use words such as carnivore, herbivore and omnivore in the discussion that is
wonderful. However, it is not the point of this exercise that they learn this vocabulary. Instead we
want them to make observations and draw their own conclusions as to what each animal eats from
the evidence in the skulls.
Nose:
Ask students what the nose is for. It may be obvious that it is for breathing air. But see if students
have noticed that all of the animals in front of them breathe air. So, what does that make them?
(Mammals. As opposed to fish who breathe oxygen dissolved in the water using their gills.)
Students may notice the structure inside the nasal cavity of the seal, sea lion, and otter. Ask students
if they have an idea of what that is for? It is a filter to keep water, salt, sand, etc. out of their nose.
These structures also help to warm incoming air and to add moisture to the air although the later isn’t
too important while in the water!
Find out if students know where the dolphin’s “nose” is. They may point to the end of the face. But
where does the air go in?
Pull out the raccoon skull. Ask students to compare it to the sea lion (or seal) skull. These two
animals are fairly closely related but the raccoon lives on land. What is the difference in their noses?
Students may notice:
• Raccoon doesn’t have as much filter material inside the nose
• Raccoon’s nose is more in the middle of the face, but the marine animals’ noses are higher up.
Ask students to consider reasons for the nose to be higher up on a marine animal. (So when they
come up to breathe they don’t have to put up much of their head out of the water.)
Eyes:
Students may have noticed that the dolphin’s eyes are far back on the side of its head. Why do they
think that is? Why would the others have their eyes more towards the front?
Help students discover that animals with eyes on the front of their head have good depth perception –
this allows them to know how far away their prey is. Then ask them to consider the dolphin. They eat
fish that swim around a lot. How does a dolphin know how far away their prey is? If they need help,
ask students to consider the unique shape of the dolphin skull.
The indention on the front of the skull creates a space for an organ called the melon, which allows the
dolphin to create sonar and can “see” the fish in front of them.
Sagittal crest:
Students with the CA sea lion may have noticed the fin-like bone along the top of the skull.
Ask students to brainstorm what that might be for.
Help students discover that it is an attachment point for the jaw muscles and gives the animal a very
strong bite.
Teaching Tip:
If students demonstrated a significant amount of knowledge about one of these skull features, you
may want to spend a limited time on it in this activity, or even skip it all together. It is also not required
to get to all of the skull features.
End of station warning – Observe & Apply
Timing: 3 minutes
Show the elephant seal skull (previously hidden). Do you recognize structures from other skulls in this
skull? What is that structure for? Students may notice:
• Sharp teeth similar to the sea lion and seal – good for grabbing food.
• Nose is high on the face and has a filter structure in it – so they can breathe without coming
out of the water and don’t get salt and sand in their nose.
• Eyes point forward – to be able to tell how far away prey is.
• Nose is set back on the head – which leaves support for an elephant like nose.
• There is not a sagittal crest bone like the sea lion – however, there is a second form of sagittal
crest, which is a ridge along the backside of the skull. This skull is a good example of that.
See if students have an idea of what the animal is.
Safety Net Activity: Skills: Observe, evaluate
Timing: 2 min.
Show the sample of baleen. What do you notice? How might a marine mammal find this adaptation
useful?
Students may or may not know. Show a picture of a baleen whale and see if they can explain the
purpose of the baleen with this new information.
Help them discover this is the “teeth” for an omnivorous marine mammal. These whales eat plankton
which contains both algae and animals by taking a mouthful of water. They push the water back out
through the baleen, which catches all the yummy parts.
Background Information
What is a skeleton?
A skeleton is a strong frame that supports and protects an animal’s body. All mammals, including marine
mammals, have the same general design of skeleton frame. The mammal skeleton is internal, or inside the
body, and includes: the skull, the spine, the ribs and four limbs.
Skull: The skull is the most complex part of the skeleton. The skull is a hard casing of fused bones. It protects
the brain and houses the sensory organs – the eyes, ears and nose. It provides openings for breathing and
eating as well as an anchor for the teeth.
Spine: The “backbone.” The main support for the body, where all the other parts of the skeleton attach. A spine
is made up of several vertebrae linked together in a long flexible column. The spine identifies the animal as a
vertebrate.
Ribs: A protective cage around the heart and lungs.
Limbs: Allows the animal to move around and explore its environment.
Muscles attach at all different parts of the skeleton providing the necessary forces for movement of that part.
What are some basic characteristics of "marine" mammal skeletons?
Marine mammals are unique from other mammals in that they are adapted for a lifestyle primarily in the ocean
environment. Their body shapes (and thus the skeletal frame that helps define the shape) are streamlined with
minimal protuberances. These torpedo or submarine-like bodies move efficiently through the water with
minimal resistance. Most marine mammals don’t have arms or legs, but flippers - another adaptation to
optimize swimming. However, if you look at the bone structure within their skeletons, they have bone structures
that resemble the arm and leg bones of humans. They are shaped a little differently however, flattened and
shortened- to help form the paddle-like flippers. Because whales live exclusively in the water, they have lost
almost all trace of their hind limbs (legs), but if you look closely at some whales’ skeletons, you can see
remnants of their leg bones. These “vestigial” leg bones, are evidence that millions of years ago whales lived
and walked on land, but then returned to the water probably because of food supply. Dolphin and whale skulls
are unique among mammals because their nostrils or “blowhole” is positioned on top of their skulls, well
removed from the snout. This important adaptation allows them to breathe without emerging from the water.
The rib cages of deep diving marine mammals, particularly whales, tend to be more flexible as compared with
other mammals. This allows for tremendous expansion of the lungs, as well as the ability to collapse their lungs
during deep dives. A baleen whale’s rib cage is particularly flexible with few attachments to the sternum (breast
bone). A stranded baleen whale may suffocate easily when beached as the rib cage collapses under the
whale’s own weight.
What is a marine mammal’s skeleton made of?
A marine mammal’s skeleton is made primarily of bone, just like humans and other mammals. Bone is a strong
hard substance made with calcium and other minerals. Most marine mammals’ bones tend to be oilier than
human bones because of all the blubber they store for warmth, food reservoirs and buoyancy. Whale bones
can also be spongier than land mammal bones, because the bones do not have to be as strong as land
mammals whose bones need to support them on land. Because of the oil content and the surrounding marine
environment, whale bones tend to decompose more quickly. It is rare to find a completely intact whale
skeleton.
Why study skulls and bones?
Bones last much longer than other parts of the body because they decompose or breakdown much more
slowly due to the minerals in the bone. Bones, or fossils of bones, are frequently the only record left of animals
that lived a long time ago. Bones, especially the skull, can tell us a lot about an animal and it’s lifestyle. The
bones tell us the approximate size and shape of the animal, what types of food it might eat, what senses it may
have relied on most, any special adaptations it may have to the environment (like the blowhole in the whale),
and many other things, including even how it might have died.
MARINE MAMMAL SKULLS
PINNIPED SKULLS – Elephant seal, Harbor Seal, California Sea Lion
Pinnipeds are excellent hunters and their skulls give us several clues to this skill. They are carnivores, with
strong canine teeth set in strong jaws to catch their diet of mainly fish. Pinnipeds typically catch and swallow
their food whole, so they don’t have very specialized “chewing” teeth (molars). Sometimes the teeth posterior
to their canines, are referred to as postcanines since they are not highly specialized for chewing. The number
of teeth in a pinniped is less than most other mammals.
Pinnipeds skulls are shaped so their eyes and nose are near the top of their head so they can stick them out of
the water easily. Pinnipeds tend to have very large eyes to help them see their prey underwater. Note the lacy
bones (the turbinates) in the nasal cavities of the pinniped skulls. These are the animal’s air filtering system.
The turbinates are lined with mucous to warm the air when the pinniped inhales, and to prevent salt and sand
from entering the respiratory system.
ELEPHANT SEAL
This is a male skull. The male can be up to three times larger than the female, so the male skull is typically
much larger than the female skull.
Elephant seals are named for the mature male’s huge nose. At about age nine, the male’s snout becomes
greatly enlarged into what is called a proboscis. The proboscis is inflatable, and serves as a resonating
chamber for the male’s deep-throated vocalizations made during the mating season. The proboscis is made of
soft tissue and is not part of the skull, but lies on the snout portion of the skull.
This skull shows the massive, powerful jaws and huge canine teeth of the male. These teeth and jaws are not
only important to help them catch their diet of fish and squid, but they are also useful for their mating battles.
The males slash and bite at each other’s chests with their giant mouths to establish who gets the female
elephant seals.
HARBOR SEAL
California’s smallest pinniped, it has strong canine teeth to help catch and hold its diet of fish, crab, octopus
and squid.
Seal and sea lion skulls are very similar, and hard to tell apart. There are a few differentiating features
including no prominent ridge above the eye socket (no supraorbital process) on the seal, which is present on
the sea lion skull; and no bony ridge on top of the head (sagittal crest) on the seal skull, present on the male
sea lion skull. See if the students are able to tell the seal skull and sea lion skull apart given these clues.
Seals move on land by “hopping” on their bellies looking more like giant caterpillars. They are unable to rotate
their hind flippers forward, like sea lions do, because of the strong tension of a tendon running through a
groove in the ankle bone. Seals use their hind flippers for power swimming, and their front flippers for steering.
CALIFORNIA SEA LION
This is an adult male skull as can be identified by the bony ridge on the top of its skull called the sagittal crest.
The sagittal crest is where the jaw muscles attach at the top of the head. The adult male has very powerful
jaws. Male sea lions need powerful jaws to battle for female sea lions.
A sea lion’s age can be determined by its teeth. They secrete a layer of cement on the insides of their teeth
each year. When the sea lion dies, you can look at a cross section of a tooth, much like growth rings on a tree,
to determine its age. Note the strong canine teeth that come in handy to catch and hold fish and squid before
they are swallowed.
A sea lion is able to “walk” on land due to its ability to rotate its hind limbs forward and use them like long “feet”.
When the sea lion swims his hind flippers are rotated backwards, behind his body, so he can use them like a
rudder. The front flippers provide the main power for swimming.
CETACEAN SKULLS – Dolphin, Baleen Whales
"The Marine Mammals Feeding Methods" poster shows the two different types of whales, toothed and baleen,
and their contrasting feeding techniques. There are also two different types of tongs to illustrate the two
different types of jaws and feeding techniques.
Whales are classified into two different groups based on their teeth: Toothed whales (odontoceti) and baleen
whales (mysticeti) The toothed whales eat primarily fish and squid, using their teeth to catch and grip their
prey, then swallow the food whole, not using their teeth for chewing. The baleen whales are filter feeders, using
the baleen like giant sieves. They draw in seawater through their giant mouths, and spit it out back through the
baleen, trapping krill, fish, and other small ocean creatures inside the baleen plates.
The whale skull is probably the most modified among mammals, and is a massive skull. The skull is
“telescoped” with elongated jaws and a shortened braincase. One of the most striking features is the position
of the nostril, which may be single (odontoceti) or double (mysticeti) nasal passage which forms a single
“blowhole.” The blowhole is typically placed on the highest point of the head, well removed from the snout.
DOLPHIN
The dolphin skull is streamlined. It has a long narrow jaw, like the neck of a bottle (hence bottle-nosed dolphin),
with about 50 pair of round pointed teeth. Ask the students how they think the dolphin uses his teeth. (These
sharp peg-like teeth allow it to grip slippery fish and squid until the prey can be swallowed whole. These teeth
are not designed for the tearing and chewing of food like ours.) One of the most striking features of a dolphin’s
skull (and all cetaceans’ skulls) is the position of its nostril. The two nasal passages merge into one that opens
to the top of the skull as one blowhole. Ask the students to find the blowhole and give a reason why this is such
a good adaptation for the dolphin (allows them to breathe without emerging from the water).
Sound is a very important sense to the dolphin. Sound travels well underwater, and allows the dolphin to “see”
long distances underwater with a process called echolocation. This is very helpful in locating food especially in
murky or deeper waters (Please see the "Echolocation" poster for details on echolocation). Point out to the
students how the dolphin skull is designed to optimize these echolocation skills. The skull is concave on top
(no “forehead”) to allow space for the melon that then creates the dolphin’s forehead. When the sound waves
return, the dolphin receives the sound through its lower jaw, not an external ear. Show the students that the jaw
is hollow, filled with an oil of similar density to seawater, to optimize sound transmission. Also note that the
angle of the lower jaw is optimized to capture the maximum amount of returning sound waves. Show how the
jaw leads right up to the inner ear to deliver the sound waves. In the whale family, to which the dolphins
belong, only odontocetes (toothed whales) have shown the ability to echolocate.
Note the position of the dolphin’s eyes. They are placed far to the sides. This gives them a wide field of view
allowing the dolphin to see forward, to the side and also somewhat to the rear. This helps them survive in their
watery environment.
SEA OTTER
The sea otter has strong jawbones to help them crush the shells of crabs, abalone, clams and sea urchins.
They have several different shaped teeth good for tearing, ripping and chewing their food. The incisors, the
front teeth, are good for scooping the meat out of shells.
Individual otters have their own favorite foods. Each otter may eat only two or three different types of food. Sea
otters’ teeth are often stained to match their favorite food. If a sea otter 's teeth are tinted purple, he probably
likes purple sea urchins. Otters that feast on crab and squid tend to have whiter teeth. These feeding habits
may also explain why several sea otters can live in one area peacefully, since they are not always hunting the
same food, they are not always in direct competition.
The sea otter, unlike most of its other marine mammal counterparts, has paws, not front flippers, and they use
them to help catch and hold their food. The sea otter is also one of the few mammals who uses tools, such as
a stone, to help it to open its food.
The sea otter has a very flexible spine or backbone. This lets them reach all parts of their body so they can
clean their fur. Keeping their fur clean is very important in keeping them warm, because otters have no blubber.
Otters blow and pat small bubbles into their fur while somersaulting and grooming to keep themselves warm
and insulated. This flexible backbone also means they can do all sorts of fancy tricks, performing forward and
backward somersaults and twisting while swimming in the water.
Note on the poster with the sea otter skeleton that the outside toe is the longest, and inside toe is shortest, just
the opposite of humans. With a large outer toe, an otter can spread its webbed feet wider for swimming. This
toe design does not work well for walking though, and would make us wobbly!
Standards
LS4.C: Adaptation – For any particular environment, some kinds of organisms survive well, some
survive less well, and some cannot survive at all.
LS3.B Variation of Traits – Different organisms vary in how they look and function because they have
different inherited information.
The environment also affects the traits that an organism develops.
Possible pictures should they need replacing. All URLs gotten with advanced Google search for free
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