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Vertebrates. Mammal evolution. Originated in the ocean Land vertebrates descended from bony fishes On land, evolved 2 pair of limbs = tetrapods (4 footed) and lungs. Some amphibians evolved into reptiles, some reptiles into mammals or birds

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Mammal evolution


Originated in the ocean

  • Land vertebrates descended from bony fishes
  • On land, evolved 2 pair of limbs = tetrapods (4 footed) and lungs

Some amphibians evolved into reptiles, some reptiles into mammals or birds

  • At some point, land tetrapods reinvaded the ocean = marine tetrapods
marine mammals
Marine Mammals
  • Evolved from reptiles about 200 million years ago

4500 species of mammals

  • Endotherms (warm-blooded)
  • Have hair on their skin
  • In relation to body size, brain is larger and more complex than in reptiles

Viviparous – bear young that are developed inside the mother’s body

  • Baby mammals feed on mother’s milk
  • Seals
  • Sea Lions
  • Walruses
  • Largest group of pinnipeds (seals, sea lions, and walruses)
  • 19 different species
Rest, breed, and bear young on land
  • Land-breeders – form a “harem” with a large lead male
Bristly hair on body and face
  • No external ear
  • Short neck
  • No external testicles in males

Predators – feed mostly on fish and squid

  • Nostrils close automatically and pupils expand widely under water
  • Can remain under water for 1-2 hours due to large spleen storing oxygen-rich blood
  • Paddle-shaped for swimming
  • Rear flippers do not move forward, so they cannot “pull” themselves onto land
Anterior flippers covered with hair, 5 toes with sharp nails, and cannot be rotated backward
Most live in cold water
  • Thick blubber – keeps them warm, helps with buoyancy, and serves as food reserve for weeks

Hunted for their skin, meat, and oil from their blubber

  • Make and hear sounds under water used for simple communication (from barks and wails to complex songs)
  • Still unknown if use reflected sound waves or echolocation for underwater navigation and to track prey
elephant seal
Elephant Seal
  • Largest of pinnipeds – up to 20 ft. and 4 tons

(The Internet is full of recent data.)


Almost exterminated for their blubber, and only 100 remained in 1890

  • Because of protection, almost 100,000 now on California’s coast
monk seal
Monk Seal
  • Live in warm regions
  • Rare
  • Endangered
  • Carribean Monk Seal – last seen in 1952
harp seal
Harp Seal
  • Give birth to white, furry pups on floating Arctic ice
  • Pups grow fast and shed fur before ice melts
Uses front flippers in swimming – no hair or nails on the edge
  • Front flippers can rotate backward to help support weight and keep head up
  • External testicles present in males
Have external ears
  • Have a longer neck than seals so can support their head upright
Graceful and agile swimmers using mostly their broad front flippers (seals use their back flippers to swim)
fur seals
Fur Seals
  • 9 species
  • Really sea lions with a thick underfur
california sea lion
California Sea Lion
  • Most familiar fur seal
  • Found off the Pacific US coast and Galapagos Islands
  • Large with a pair of tusks
  • Stiff whiskers on snout act as feelers when eating
Mostly eat clams and bottom invertebrates
  • Suck their food into their mouths as they move along the bottom
Habitat is on the edges of the ice pack in the Arctic
  • Migrate south during winter
  • Hunted legally by natives