Marine MammalsMarine Mammals

The ancestors of marine mammals lived on landThe ancestors of marine mammals lived on land

• whales and dolphins: 60 mya- oldest marine mammals

- evolved from hyena-like land animals

• seals, sea lions: 20-25 mya- evolved from bear-like ancestor

• sea otters: 5-7 mya- evolved from weasel-like ancestors

(manatees … grass-eating elephant-like ancestors 50 mya)

• Whales & dolphins: most modified from land mammals

► nostrils moved to top of head (blowhole) ► recognizable, modified arms/hand-bones in flippers ► upper leg bone still present in some species ► fur/ whiskers still seen in embryo ► no external ears

use blubber to stay warm

• Seals: somewhat modified from land mammals

► nostrils near mouth ► fore-flippers (finger bones) and back flippers (w/ distinct toes) ► fur and whiskers, and blubber to stay warm ► external ears often still visible ► portion of life on land

• Sea otters: similar to terrestrial relatives

► other than webbed feet for swimming, very closely resemble land-dwelling relatives in the weasel family ► unlike whales and seals, sea otters do not have blubber to keep them warm

Cetacean Evolution

Cetaceans = whales, dolphins, and porpoisesCetaceans = whales, dolphins, and porpoises

Latin "cetus" (a large sea animal)

• Ancestor of cetaceans = hyena-like pakicetid

• Pakicetids = land animals with hoof-like claws likely hunted along the shore for fish

• Over time, pakicetids moved farther into the water (food? predators?) & began to adapt to aquatic environment

• Over millions of years - evolved into a primitive group of whales archaeocetes small, seal-like animals, with four legs and few marine specializations

• Paddle-like flippers replaced limbs to help them move in water

• Uultimately evolved into whales

pakicetid

whale

2 groups of cetaceans

mysticetes (baleen whales)mysti from Greek word moustache

have keratin plates to strainplankton, krill and smaller fish

e.g. humpback whales blue whales grey whales

odontocetes (toothed whales)

feed on fish & squid

e.g. orca dolphins & porpoises sperm whales

Cetaceans have lost external ear-

• sound waves travel faster in water than air- external ear not needed

• inner ear - so well developed that cetaceans hear sounds tens of miles away & can discern direction sound comes from

Some cetaceans use echolocation-

• emit a sound which bounces off an object and returns to them through jawbone to ear

• can discern size, shape and movement of the object, & catch fast-swimming prey in total darkness (dolphins: bb pellet vs. corn kernel 50 ft away)

Cetaceans have lost the fur of their terrestrial ancestors

• to keep warm in cold ocean waters thick layer of insulating fat• fat serves to sustain animals over periods of fasting when food is scarce

Cetacean milk, on average, contains 40% fat

Cow milk =

Human milk =

Why so much fat in milk??

4% fat

2% fat

• cetaceans nurse underwater– cuts down on feeding time

• young need to quickly put on fat for insulation against cold

• fuels rapid development- increases chances of young surviving (grey whales gain 8 lbs per hr nursing & some whales double their birth weight in 7 days! - humans 180 days to double)

How is being a whale in the ocean similar to being a kangaroo rat in the desert?

getting fresh water is a major challenge

• highly lobulated kidneys= “super-filters” -remove excess salts

• fresh water from fish eaten

• the metabolism of fats liberates water

Breathing and DivingBreathing and Diving

cetaceans dive to incredible depths while feedingcetaceans dive to incredible depths while feeding

• blowholes close underwater

• heart beat slows - up to 50% of normal

• blood vessels constrict - blood sent only to essential organs

• metabolism and body temp. drop – less oxygen used

• stored oxygen in the myoglobin of muscles released

Migrations

Many whales migrate thousands of miles each year– e.g. humpbacks and grey whales travel up to 14,000 miles round-trip each year in their migrations

• summer months- whales feed in Arctic waters

• travel to low-latitudes to give birth in warm waters (Baja Mexico)

• calves born with little blubber- need warm, protected waters

seals, sea lions, walrusseals, sea lions, walrus

“pinnipedia” = Latin as "fin foot”

PINNIPEDS

Three families of living pinnipeds –

Phocidae (earless seals or true seals) e.g. elephant seals, harbor seals• no external ear flaps• small front flippers• move on land by “galluphing”- wormlike undulating motion• Can not bend hind flippers forward

Otaridae (eared seals) e.g. sea lions• external ear flaps• large front flippers that help seal move on land• can rotate the hind flipper forward to use pelvic bone to move on land

Odobenidae (walrus)

All pinnipeds come ashore to breed, give birth and nurse their young!

In California, our main pinnipeds are:

• elephant seals

• sea lions

• harbor seals

Sea Otters – most recently moved to sea

Scientific Name:

Enhydra lutris

Very similar to ancestors in weasel family:

• carnivores: strong canine teeth for tearing food, flat molars for crushing

• external ears

• fur and whiskers

• arms and legs rather than fins

Adaptations for living in the water

• flattened tail and flipper-like hind feet for propulsion

• lung size: 2.5 X the size in land mammal relatives

Keeping Warmsea otters don’t have blubber

extremely thick fur - about 600,000 per square inch!!

keep warm by trapping air beneath their thick fur- trapped air acts as a layer of insulation

must eat 20 - 25 % of their body weight each day to maintain a high level of internal heat production to stay warm

Feeding

• one of only a few animals known to use tools

• generalists: feed on about 40 different marine invertebrates

• generally forage for food in depths of 60 ft. or less

• use tools to dislodge prey from rocky areas, open shells

• have a loose pouch of skin under each foreleg which is used to hold food items gathered from the

sea bottom

 

Female otters live 15-20 years and males 10-15 years

Max. sea otter weight = about 100 lbs.

• sea otter females will mate with one-several males

• she will have her first pup around age 4 and continue to reproduce until about age 15

• gestation is about 7 months and pups are dependent on the mother for about 5 months post birth

NEXT UP….. ELEPHANT SEALS