Chapter 9

• Mammal


  Superior vertebrate (Homeothermic and amniotic) with skin rich in epidermal glands; covered with hair; feed his young with milk produced by his own lacteal glands
• The numeric importance of the class Mammalia is poor (c.3500 living species), but the moral importance is great as the class contains the species Homo sapiens which is crowning the genealogical tree of the Animal kingdom
• The study of the structure and the evolution of Mammals mean knowing about the history of our species
• The Mammalian type is issued from the reptilian Theropsid lineages
• It is easy to distinguish a reptilian from a mammalian, but the problem of evolution and passage from reptiles to mammals is a matter of special concern
• This problem cannot be solved unless if certain analysis of bone anatomy are diagnosed
• General characteristics of mammals

  • Skin with hair
  • Teeth in sockets
  • Seven neck vertebrae
  • Ears with three middle-ear bones
  • Limbs typically with five digits
  • Heart four-chambered, single aortic arch on left
  • Red corpuscles nonnucleated
  • Coelom divided by muscular diaphragm
  • Larynx at upper end of trachea
  • Pelvis fused to sacrum, pubic bones fused ventrally
  • With urinary bladder, urine liquid
  • 12 pairs of cranial nerves, brain elaborate
  • Endothermal
  • With external genitalia
  • Fertilization internal
  • Eggs amniote
  • Some oviparous
  • Mostly viviparous
  • Young nourished by milk from mammary glands
• Three characteristics unique to mammals

  • 3 middle ear bones
  • Hair
  • Production of milk by mammary glands
• Middle ear bones


  Malleus, incus, and stapes (hammer, anvil, and stirrup) function in the transmission of vibrations from the tympanic membrane (eardrum) to the inner ear
• Mammalian hair


  Present in all mammals at some point in their development, functions include insulation, color patterning, and aiding in the sense of touch
• Mammary glands


  Produce milk to nourish newborn offspring, female mammals invest a great deal of energy caring for each of their offspring
• The skin of mammals is constructed of two layers, a superficial nonvascular epidermis and an inner layer, the dermis
• Hair


  Derived from an invagination (pocketing) of the epidermis termed a follicle, composed of keratinized cells that may be cylindrical or more or less flattened
• Types of mammalian hair

  • Guard hairs
  • Underfur
  • Vibrissae (whiskers)
• The "horn" of the rhinoceros is composed of a fibrous keratin material derived from hair
• Examples of keratinized derivatives of the integument other than hair

  • Horns
  • Hooves
  • Nails
  • Claws
  • Baleen
• Horns


  Outgrowths of localized thickenings of the horny skin layers, can be entirely epidermic, bony but covered with epidermis (hollow or not hollow but temporary)
• Hooves


  Specialized keratin pads on the toes of ungulate mammals, protecting the toe and cushioning it from impact
• Types of ungulate mammals

  • Artiodactyls (even-toed)
  • Perissodactyls (odd-toed)
• Nails and claws


  Horn-like envelopes covering the tips of the fingers and toes, made of keratin
• Integumentary glands in mammals

  • Mucus glands
  • Excretory sweat glands
  • Oil secreting sebaceous glands
  • Mammary glands
• Sebaceous glands


  Produce a lipid mixture called sebum that is secreted onto the hair and skin for water resistance and lubrication
• Sweat glands


  Small tubular structures of the skin that produce sweat, of two main types: eccrine (produce water-based sweat) and apocrine (produce sweat with nutrients for bacteria)
• Mammary glands


  Produce milk to nourish newborn offspring, present in both sexes but functional only in females, number varies by species
• Dentition


  Development of teeth and their arrangement in the mouth
• Types of dentition


  • Homodont (all teeth same type)
  • Heterodont (teeth differ morphologically)
  • Polyphyodont (continuously discarded and replaced)
  • Diphyodont (two successions of teeth)
  • Monophyodont (one set of teeth throughout life)
• Types of teeth


  • Incisors (cutting)
  • Canines (stabbing)
  • Premolars and molars (crushing and grinding)
• Carnassial teeth


  Modified last upper premolar and first molar in lower jaw of some carnivores, used for cracking bones and shearing tendons
• Dentition adaptations by feeding habit

  • Carnivores (sharp incisors, pointed canines, compressed molars and premolars)
  • Rodents (elongated, ever-growing incisors, no canines)
  • Deer (flat, chisel-like incisors, large grinding molars)
• Thecodont dentition


  Teeth lodged in bony sockets or alveoli of the jaw bone, found in mammals and some other vertebrates
• Limb adaptations in mammals

  • Fins (for swimming, sea lions)
  • Wings (for flying, bats)
  • Palettes (for digging/burrowing, moles)
  • Jumping (kangaroos)
  • Climbing (gibbons)
• Digestive system variations


  • Ruminant (four-chambered stomach)
  • Non-ruminant (simple stomach)
  • Gall-bladder presence/absence
  • Importance of ileum and caecum
  • Ramified pancreas (rabbits)