Mammals

• Because learning changes everything.
• Mammals: Synapsid Amniotes
• Platypus, elephant


  • Unique and interesting species
• Prototherian, metatherian, and eutherian reproductive strategies


  • Costs and benefits
• Many of the characteristic (often unique) mammalian functions are tied to the structure and functions of mammalian integument and musculoskeletal systems.
• The uniqueness of mammals is tied to their behavioral and reproductive functions.
• Mammals are a relatively small group
• Cenozoic = age of mammals
• Mammals are the most massive of all animals today or that ever existed
• Elephants


  • Largest land mammal
• Pygmy shrew, Kitti hog-nosed bat

  • Smallest mammals
• Ways mammals are affected by human activities

  • Beasts of burden
  • Clothing
  • Domestication
  • Education
  • Food
  • Pets
  • Research
  • Hunting
  • Alien animals
  • Pleistocene extinctions
  • Modern extinctions
• Mammal-like reptiles


  • Shared many skeletal features with mammals
  • Many reptiles had hair (none today do)
  • Mammals have a lower jaw consisting of a single bone with articulation between the jaw and squamosal bone
• Mammals first appeared


  200 MY ago
• First mammals very closely resembled their reptile ancestors
• For 160 MY mammals lived in the shadow of the dinosaurs
• When dinosaurs vanished near the beginning of the Cenozoic, mammalian diversity greatly increased
• Mammals were now agile, more intelligent, warm-blooded, well insulated, and suckled their young
• Separate lines of mammal origin and evolution

  • Prototheria (egg-laying mammals with poor thermoregulation)
  • Theria (all others)
• Mammalian skin and derivatives

  • Thicker and more complex than in other vertebrate groups (or any other animal)
• Hair


  • Some facial hairs (vibrissae) became sensory in function
  • Grows from a follicle in epidermis and dermis
  • Made of keratin (protein)
• Types of hair


  • Underhair (dense and soft for insulation, traps layers of insulating air)
  • Guard hair (coarse and long, protection against wear, coloration)
• Defensive hairs


  • Porcupines, hedgehogs
• Horny or bony plates

  • Armadillo, pangolins
• Mammals that have lost most of their fur

  • Hippos, elephants, porpoise, humans
• Shedding (molting)


  • Foxes and seals (1x/yr)
  • Most mammals have 2 annual molts (spring - replaced by thinner hairs, fall - replaced by thicker hairs)
• Types of coloration of hair

  • Protective camouflage (arctic - white, outside arctic - somber colors)
  • Disruptive camouflage (leopard spots, tiger stripes, fawn spots)
  • Warning (skunk)
• Modified hairs


  • Bristles of hogs, spines of porcupines, vibrissae (whiskers) - tactile, sensory hairs
• Horns


  • Found in only 5 families of ungulates
  • Unbranched, hollow sheaths of keratinized epidermis (same as hair, scales, feathers, claws, nails, hooves)
  • Grow continuously throughout life
  • Not normally shed, do not regenerate if cut off
• Antlers


  • Entirely bone, with no keratinized layer covering it
  • Tend to be large complex and ornate
  • Used mainly for sexual display during mating season
  • Living tissue, sensitive to touch and pain
• Giraffe horns


  • Antler-like but retain skin covering, are not shed
• Sweat glands (eccrine glands)

  • Important in warm-bloodedness, temperature control
  • Especially on hairless regions, e.g. foot pads
  • Heat regulation, part excretory organ
  • Simple, tubular, highly coiled
• Scent glands


  Significance among mammals
• This lesson reminds me of...
• The skull and teeth of mammals
• Mammals have three middle ear ossicles
• Mammals have a secondary palate, not homologous to the archosaur secondary palate
• Homodont teeth


  Uniformly conical
• Heterodont teeth


  Specialized for different functions
• Deciduous (milk teeth) and permanent teeth


  Single replacement of teeth is the diphyodont condition, polyphyodont in reptiles