Mammals

• Mammal Traits

  • Hair
  • Larger brain & middle ear bone
  • Specialized teeth & jaw
  • Mammary gland & placenta
• Order of mammal evolution

  1. Pelycosaurs

  2. Therapsids

  3. Cynodonts

  4. Diphyodonts
• Cynodont


  • Paleozoic surviving therapsid
  • Erect gate with limbs underneath
  • Increased metabolic rate
  • Enhanced jaw & skeleton (heterodont)
  • Secondary palate — breathe while eating
  • Turbinate bones in nasal cavity — heat retention
  • Loss of lumbar ribs — increase in vertebral flexibility & diaphragm evo
• Diphyodont


  • Mouse-like cynodont
  • Jaw & teeth reorganization — deciduous
  • Ear bones: Malleus + incus — previous jaw joints, efficiency, Stapes — homologous to columella, hearing
  • Endothermic + hair + mammary glands
  • Body temp less than 98
  • Hatched from eggs
• Cenozoic Radiation in Eocene after the Cretaceous extinction because of the open dinosaur niche
• Skin/Hair


  • Epidermis + Dermis (keratin @ areas with most wear)
  • Hair = epidermal structure (molt twice in spring & fall)
  • Hair layers = medulla + cortex + cuticle
  • Hair follicle: deep in dermis, rapid proliferation @ base for growth
  • Hair is dead & stays in follicle until new proliferation occurs
• Types of hair


  • Underhair — soft & dense for insulation
  • Guard hair — long & coarse to protect, give color & shape
• Specialized guard hair

  • Whiskers/vibrissae & quills
• Rhino horn

  Hairlike, keratinized filaments (NOT TRUE HORNS)
• Antlers


  (deer) skull extension, males shed after breeding season
• Glands


  • SWEAT = unique to mammals, tubular & highly coiled
  • SCENT = communication
  • SEBACEOUS = @ hair follicles or open onto skin surface
  • Mammary = modified apocrine
• Eccrine sweat glands


  Hairless regions, watery fluid to draw heat away
• Apocrine sweat glands


  Open to hair follicles, milky fluid for reproduction
• Sebaceous glands


  Glandular cells secrete sebum all @ once when mature
• Mammary glands


  Exception — monotremes with milk line
• Migration


  Not the norm (except for caribous, fur seals, & gray whales)
• Echolocation


  • High frequency pulses & clicks
  • Bats, dolphins, toothed-whales
  • Coevolution of ultrasonic sensors in moths
• Flight


  • Bats—true flight
  • Rodents & marsupials—gliders
  • Patagium: skin flaps of gliders
• Populations


  • Clumped, even, or random
  • Community = 3+ populations
  • Density-dependent factors = competition, disease
  • Density-independent factors = environmental
  • Births + Immigrations = increase #
  • Deaths + Emigrations = decrease #
• Territory


  Smaller, "home"
• Home range


  Larger, neutral zones of habitat
• Food & Feeding


  • Insectivore ancestor
  • Specialists or generalist
  • Homodont reptiles —> heterodont mammals: Incisors = sharp, Canines = piercers, Premolars = compressed crown for sheering, Molars = grinding
  • Longer digestive tract in herbivores: reduced or absent canines, Cellulose fermentation chambers
  • Smaller animal = faster metabolism, increased food consumption
• Reproduction


  • Mating Seasons = when resources are plentiful to rear young
  • Males = no season necessary
  • Females = cyclic (have heat/ESTROUS): Polyestrous = wild pigs, rodents, Monoestrous = dogs, fox, bats
• Reproduction patterns


  • Monotremes: (UNPREDICTABLE CLIMATES) monoestrous, lay 2 eggs each breeding season
  • Marsupials: choriovitelline placenta = mimics yolk sac, embryonic diapause: pause in devo, waits for joey to crawl out of pouch
  • Eutherians: (PREDICTABLE CLIMATES) Prolonged gestation & parental care, placental nourishment, increase in size = longer gestation & less young (humans have longest)