Marine Mammals

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Marine Mammals
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The ancestors of marine mammals lived on land
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• 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

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• 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

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• 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

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• 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

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Cetacean Evolution

• Cetaceans whales, dolphins, and porpoises
• Latin "cetus" (a large sea animal)

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• 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
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2 groups of cetaceans
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• 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)

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• 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)

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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

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Breathing and Diving cetaceans dive to
incredible depths while feeding

• blowholes close underwater

• blood vessels constrict - blood sent only to
  essential organs

• heart beat slows - up to 50 of normal

• metabolism and body temp. drop less oxygen used

• stored oxygen in the myoglobin of muscles
  released

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• 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

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PINNIPEDS
seals, sea lions, walrus pinnipedia Latin as
"fin foot
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• 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

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All pinnipeds come ashore to breed, give birth
and nurse their young!
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In California, our main pinnipeds are

• elephant seals
• sea lions
• harbor seals

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Sea Otters most recently moved to sea
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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

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• 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

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Keeping Warm
sea otters dont 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
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• 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
•  

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Female otters live 15-20 years and males 10-15
years Max. sea otter weight about 100 lbs.
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• 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

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NEXT UP.. ELEPHANT SEALS