Mammals Have a Body Covering of Hair, Maintain a Constant Warm Body Temperature, and Nourish

Key Concepts

•Mammals have a body covering of hair, maintain a constant warm body temperature, and nourish their young with milk produced by the mammary glands of the mother.

•Sea otters have thick coats of fur and feed on marine invertebrates near shore.

•Polar bears feed mainly on seals and are top predators in arctic food chains.

•Pinnipeds have limbs modified to form flippers, and are better adapted to life at sea than to life on land.

•Sirenians are totally aquatic mammals that feed on a variety of aquatic vegetation.

•Cetaceans have a fish-like body shape and are the mammals most suited to life in the sea.

•Special physiological adaptations allow cetaceans to dive to great depths and to remain submerged for long periods.

•Cetaceans are intelligent animals that display a range of behaviors for communication and investigating their environment.

•Some cetaceans use echolocation to navigate, find prey, and avoid predators.

•Baleen whales have plates of baleen instead of teeth and feed primarily on plankton, such as krill.

•Toothed whales have teeth allowing them to feed on larger prey, primarily fish and squid, although killer whales will eat marine birds and mammals.

•Dolphins are intelligent animals that are capable of learning and sophisticated intraspecies communication.

Characteristics of Marine Mammals

•Most have hair insulating body

•Homeothermic

•Mothers produce milk for their young

–mammary glands

•Placental mammals

–placenta

•Feed at various trophic levels

Sea Otters

•Enhydra lutris; order Carnivora

•Found from California coast to the Aleutian Islands

•Short, erect ears

•Dexterous 5-fingered forelimbs

•Well-defined hind limbs with fin-like feet

•Have thick fur with an air layer for insulation

•Usually stay within a mile of shore

•normally give birth to 1 pup on shoreline rocks, and it soon follows its mother into the sea

•Eat nearly 25% of their weight in each day

–sea urchins, molluscs, crustaceans, fish

•Diurnal, gregarious, vocal and playful

•Nearly hunted to extinction for fur

Polar Bears

•Ursus maritimus; order Carnivora

•Top predators in Arctic food chains

•Adult male may be ~3 meters and 725 kilograms

•Live on shifting ice sheets and floes

•Well adapted to cold environment

–large body

–black skin

–dense layer of under-fur

Polar Bears

•Eats mostly seals

•In spring, males compete for available females

•Give birth usually to 2 cubs each weighing 1 lbs

•Climate change causing shrinkage of ice sheets

•Considered endangered

Pinnipeds: Seals, Sea Lions, and Walruses

•Order carnivora; Suborder Pinnipedia

–seals, elephant seals, sea lions and walruses

•Mate, give birth and molt on land

•Eat fish, larger invertebrates

•Predators - sharks, whales and humans

Pinniped Characteristics

•3 families:

–eared seals (Otariidae)

–true seals (Phocidae)

–walruses (Odobenidae)

•Eared seals have small external ears

•True seals lack external ears

•Spindle-shaped bodies

•Many have thick layers of fat

•Round head is carried on a distinct neck

•Large brains, well-developed senses

•2 pairs of limbs are modified into flippers

Swimming and Diving

•Fast swimmers and expert divers

•Adaptations for diving

–exhale before diving

–metabolism slows and heart rate decreases

–blood is redistributed

•Have much more oxygen in their muscles than humans

Reproduction in Pinnipeds

•Most congregate on well-established breeding beaches to mate/give birth

•Some species are polygynous

•Males arrive to establish territories

•Females give birth to pups conceived the previous year, then mate again

•Gestation is about 1 year

•Seasonal delayed implantation

•Lactation period varies

–coldest habitats = shortest lactation

–nursing stresses the mother

–some breed on pack ice, and must wean pups before it breaks up and becomes dangerous to the pups

Eared Seals

•Sea lions

–coarse coat of nothing but hair

–highly social; congregate when on shore

•Fur seals

–distinguished by thick undercoats

–coats are prized in the fur market

Phocids, or True Seals

•Forelimbs closer to the head and smaller than the hind limbs

–less adapted to life on land

–move on land by dragging their bodies

•Most congregate during breeding season;

•Harbor seals are a familiar type

•Harp seal pups have a white coat, and are thus prized in the fur market

•Leopard seal is only phocid that eats homeothermic prey, penguins, sea birds and other seals make up bulk of diet

•Elephant seals are the largest, and bulls have a unique proboscis that amplifies their roar and attracts mates

Walruses

•Lack external ears but have a distinct neck and hind limbs that can be used for walking on land

•Can grow to 3 to 5 meters in length and weigh up to 1,364 kilograms

•Canine teeth of males develop into tusks

•Typical family group is 1 bull with up to 3 females and calves of various ages

•Reproduction

–11-month gestation period

–calves with the mother for 4 or 5 years

•Found in the Arctic

•Eat fishes, crustaceans, molluscs and echinoderms

•Native people hunt them for meat, not tusks

Sirens: Manatees and Dugongs

•Order Sirenia (sirenians)

•Now confined to coastal areas and estuaries of tropical seas

•Bodies, forelimbs, pelvis similar to whales

•Completely aquatic, helpless on land

•Gentle and often trusting of humans

Dugongs

•Strictly marine

•Live in coastal areas of Indian Ocean

•Feed on shallow-water grasses

•Distinguished from manatees by:

–larger heads

–shorter flippers

–notched tail

•Only one species

Manatees

•Three species

•Inhabit both the sea and inland rivers and lakes

•Mate and give birth under water

–male remains with female

–female gives birth to 1 calf after 11 months gestation

•Strict vegetarians

•Motorboat propellers a great danger

Steller’s Sea Cow

•Extinct

•First recorded by Georg Wilhelm Steller

•Furs Steller brought from the Commander Islands attracted hunters to return

•Used Steller’s Sea Cow as a food source, and hunted the species to extinction

General Characteristics of Cetaceans

•Streamlined bodies closely resemble fishes

–blowhole

–blubber

–lack of neck

–internal ears with wax plugs

–essentially hairless

–no sweat glands

–forelimbs modified into flippers

–fluke - the main organ of propulsion

–countercurrent circulatory system with cold blood directed to un-insulated flippers conserves heat

Adaptations for Diving

•Small lungs exchange 80 to 90% of oxygen with their blood

•Lungs and rib cage collapse easily

•During a dive:

–metabolism and heart rate decrease

–blood is preferentially shunted to vital organs

•Medulla oblongata is less sensitive to CO2

–can hold breath without urge to breathe

•Large amounts of hemoglobin and myoglobin

Cetacean Behaviors

•Spy hopping

•Breaching

–serial breaching

–head lunge

•Slapping

–tail slapping or lobbing

–tail cocking

–peduncle slapp

–tail slashing/swishing

–fluke up/fluke down

–flipper flapping

–pectoral stroking

Reproduction and Development

•Limited knowledge on small whales in captivity

•Baleen whales

–Mate and give birth in the same place and time

–10-13 month gestation

•Toothed whales

–Breed throughout the year,

–7-10 month gestation

•Produce extremely rich milk

–40-50% fat, 10-12% protein

–infant grows rapidly

•Many travel in pods (groups) of adults and young

Types of Whales

•2 suborders

–Mysticeti – baleen whales

–Odontoceti – toothed whales

•Baleen whales lack teeth, and filter food from the water using baleen

–largest whales are of this type

•Toothed whales feed on larger prey

Baleen Whales

•Enormous mouths with plates of baleen

–each plate has an elongated triangular shape

–composed of keratin

–hundreds of plates form a tight mesh

–used to capture plankton, especially krill, and fish

•Feeds by swimming open-mouthed into dense groups of krill and fish

–bubble net

•Baleen is protected by the underlip

•Right Whales and Bowhead Whales

–distinguished by lack of dorsal fins

–name derived from identification of these whales as the “right whales” for hunting

–the bowhead whale is rarest whale

•Rorquals (family Balaenopteridae)

–have dorsal fin

–slender, streamlined, fast swimmers

–blue whale is the largest whale

–fin whale is second largest

–humpback whale has a hump, bosses, and very long pectoral fins

•Rorquals

–modern whaling techniques

–blue whale given worldwide protection in 1966

•Gray whale (Eschrictius gibbosus)

–only eastern Pacific population survives today

–migrate from Bering Sea to waters off Baja California to mate and give birth

–referred to as mossback whales

Toothed Whales

•Sperm whales

–3rd largest animal with massive blunt snout

–have a series of humps, no real dorsal fin

–aggressive attackers of squid and fish

–polygynous

–named for spermaceti

–ambergris

•White whales

–Beluga whales

•are unique for their white color

•northern polar seas

•main predators are killer whales and polar bears

–Narwhals

•close relatives of beluga whales

•male have tusk developed from 1 of 2 tooth buds

•narwhals also inhabit Arctic waters, eskimos only remaining predators

•Porpoises

–Related to dolphins

–porpoises have a rounded head with no beak

–harbor porpoises known for great intelligence

–widely distributed in the North Atlantic

–Dall’s porpoise might be the first animal to be protected by law

•Dolphins

–common dolphin has a definite beak

–known for encircling and following ships

–bottlenose dolphins are used in research

–orca (killer whale) is the largest dolphin

Echolocation

•Ears are modified to receive a wide range of underwater vibrations

•Dolphins emit clicking sounds

–orientation clicks

–discrimination clicks

•Echoes provide 4 types of information:

–direction from which echo is coming

–change in frequency

–amplitude

–time elapsed before the sound returns

•Dolphin can then determines object’s range, bearing, size, shape, texture and density

•Traveling dolphins move their heads side to side and up and down, scanning for objects