7' Class Mammalia 4500 species in 19 orders

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7. Class - Mammalia4500 species in 19 orders

• Characteristics
• hairy animals with glands that produce milk
• maintain constant body temp.
• most develop in the uterus where they are
  nourished by a placenta
• limbs are under the body, directed downwards
• fully mobile jaw and socket teeth

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Origins

• probably arose from therapsids (200mya) which are
  mammal-like reptiles

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• survival was probably enhanced by carrying
  embryos within the body, bearing live young, and
  the constant food supply (milk)
• by the end of the Mesozoic era (65 mya) mammals
  diverged from the original line to three groups
  (probably sub-classes) -- Monotremes, Marsupials,
  and Placentals

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1. Monotremes Subclass Protothereia, Order
Monotremata

• egg (leathery)-laying mammals
• have a sense of electroreception to locate their
  prey
• only five species exist, the duck-billed platypus
  and four sp. of spiny anteaters (Echidna)
• single hole that serves the urinary tract, anus,
  and reproductive tract

Ornithorhynchidae
(Ornithorhynchus anatinus)
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2. Marsupials Subclass Theria or Metatheria
Supercohort-Marsupialia

• the pouched animals- 272 species.
• short gestation time is due to having a yolk-type
  placenta in the mother marsupial
• young are typically born in a practically
  embryonic state (2cm).
• Ex. Opossum, koala, wallaby, wombat, kangaroo,
  and Tasmanian Devil....

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3. Placentals (subclass Eutheria)

• nourished in the uterus through a specialized
  embryonic organ attached to the uterus wall
  called the placenta allowing longer gestation
  times.
• 4000 species. whales, bats, elephants,
  armadillos, dogs, sheep, cattle, and humans....

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Order Primates

• Characteristics and origins
• 233 living species placed in 13 families
• most have long arms, prehensile (grasping) tail
  and hands with fingernails
• stereoscopic vision with eyes in front of head
• brain adapted for learning
• probably arose about 65 mya
• early primates were more like rodents that lived
  in trees

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Human classification/taxa

• Animalia
• Chordata
• Mammalia
• Primate
• Hominidae
• Homo
• sapiens sapiens

Did Humans Evolve video clip http//www.pbs.org/wg
bh/evolution/library/11/2/e_s_5.html