Mammals

• Mammals


  • Amniotes that have hair and produce milk
• There are more than 5,300 known species of mammals on Earth today
• Mammal


  A vertebrate animal whose young are nourished with milk from special mammary glands of the mother
• Derived characters of mammals

  • Mammary glands, which produce milk for offspring
  • Hair, and a fat layer under the skin help the body retain heat
  • A sheet of muscle called the diaphragm helps ventilate the lungs
  • Larger brain than other vertebrates of equivalent size, and many species are capable learners
  • Differentiated teeth
• Synapsids


  A group of amniotes that mammals belong to
• Synapsids


  • Have a single temporal fenestra, a hole behind the eye socket on each side of the skull
  • Two of the bones that formerly made up the jaw joint were incorporated into the mammalian middle ear
  • As a mammalian embryo grows, the posterior region of its jaw detaches from the jaw and migrates to the ear, where it forms the malleus

  
• Monotremes


  Found only in Australia and New Guinea, represented by one species of platypus and four species of echidnas (spiny anteaters), lay eggs, a character that is ancestral for amniotes and retained in most reptiles

  
• Marsupials


  Include opossums, kangaroos, and koalas, have higher metabolic rates and nipples that provide milk, and they give birth to live young that complete their embryonic development while nursing, in most species the nursing young are held within a maternal pouch called a marsupium
• Eutherians


  Commonly called placental mammals because their placentas are more complex than those of marsupials, young eutherians complete their embryonic development within the uterus, joined to their mother by the placenta
• Primates


  • Have hands and feet adapted for grasping, and their digits have flat nails instead of the narrow claws of other mammals
  • Have a large brain and short jaws, giving them a flat face
  • Exhibit relatively well-developed parental care and complex social behavior
• Living primates


  • Lemurs of Madagascar, lorises and bush babies of tropical Africa and southern Asia
  • Tarsiers, which live in Southeast Asia
  • Anthropoids, which include monkeys and apes
• Homo sapiens


  Humans are mammals with large brain and are bipedal, about 200,000 years old
• Derived characters of humans


  • Stand upright and are bipedal
  • Have a much larger brain and are capable of language, symbolic thought, artistic expression, and the manufacture and use of complex tools
  • Have reduced jawbones and jaw muscles, along with a shorter digestive tract

  
• Earliest hominins


  • Sahelanthropus tchadensis, lived about 6.5 million years ago
  • Australopiths, including Australopithecus anamensis, Ardipithecus ramidus, Australopithecus africanus, Australopithecus afarensis, Paranthropus boisei
  • Homo habilis, Homo ergaster, Homo erectus, Homo neanderthalensis, Homo sapiens

  
• According to one hypothesis, tree-dwelling hominins could no longer move through the canopy, so natural selection favored adaptations that made moving over open ground more efficient
• The oldest generally accepted evidence of tool use by hominins is 2.5-million-year-old cut marks on animal bones found in Ethiopia, suggesting that hominins cut flesh from the bones of animals using stone tools

  
• Other apes are capable of surprisingly sophisticated tool use, chimpanzees are even more adept, using rocks to smash open food and putting leaves on their feet to walk over thorns