Mammalian Structure and Movement

  1. Characteristics of living mammals (*diagnostic)

    1. Skeletal features
      1. Single bone in mandible*
      2. Squamosal-dentary articulation*
      3. Two occipital condyles*
      4. Long bones have epiphyses*
      5. Tendency towards fusion of bones (e.g., pelvis, cranium)
      6. Three ossicles in middle ear* (malleus, incus, stapes)
      7. Phalangeal formula: 2-3-3-3-3
      8. Secondary palate*
      9. Heterodont, diphyodont dentition

    2. Soft tissues
      1. Hair*
        1. Anatomy (See also Fig 6.2)
        2. Functions (insulation, protection, communication)
        3. Types (based on function and how they grow: definitive vs. angora)
        4. Color patterns
        5. Pigments
          • Eumelanin (blacks to browns)
          • Pheomelanin (reds to yellows)
          • Combinations (agouti)

        6. Moulting and hair replacement

      2. Glands
        1. Mammary glands
          * (two basic types in eutherians)
          e.g., cows e.g., primates
          mammary tissue mammary tissue (=lobules)
          inactive
          active
          cistern collecting ducts
          teat nipple
        2. Sebaceous glands*
        3. Sweat glands* (not all mammals)
        4. Scent glands (llama, dik-dik antorbital gland)

      3. Pinnae* (not all mammals)
      4. Endothermic with high metabolic rate
      5. Muscular diaphragm*

      6. Four-chambered heart with left aortic arch*
      7. Enucleate erythrocytes*
        slide
        colored scanning electron micrograph
      8. Large, convoluted brain
      9. Corpus callosum* connects brain hemispheres (except monotremes and marsupials)

      10. Viviparous (except monotremes)
      11. Complex placenta* (except monotremes, most marsupials)
        armadillo
        human

  2. Skeletal structure (Fig. 14.4)

    1. Basic parts
      1. Skull=cranium + mandible
      2. Postcranial skeleton=axial skeleton + appendicular skeleton

    2. Skull
      1. CNS: foramen magnum
      2. Vision: orbits, zygomatic arch
      3. Smell: rostrum, turbinal bones
      4. Hearing: external auditory meatus, auditory bullae
      5. Feeding: maxilla, mandible, zygomatic arch, sagittal crest, heterodont dentition

    3. Axial skeleton
      1. Five well-differentiated types of vertebrae
        1. Cervical (including atlas=1, axis=2)
        2. Thoracic
        3. Lumbar
        4. Sacral
        5. Caudal

      2. Ribs

    4. Appendicular skeleton
      1. Basic parts
        1. Pectoral girdle + forelimbs + manus + pollex + phalanges
        2. Pelvic girdle + hindlimbs + pes + hallux + phalanges

      2. Primitive pattern
        1. Five digits
        2. Phalangeal formula: 2-3-3-3-3

  3. Locomotion

    1. Modes of terrestrial locomotion
      1. Plantigrade
      2. Digitigrade
      3. Unguligrade

    2. Types
      1. Walking, running, cursorial (terrestrial, usually quadrupedal)
        • Many specialized for moving quickly in a terrestrial habitat
        • Pattern of footfalls depends on species and speed of travel
        • Humans are the only truly bipedal species


      2. Saltatorial (jumping, springing, bounding)
        1. quadrupedal
        2. bipedal (ricochetal)
          • enlarged feet on propulsive limbs
          • center of gravity shifted toward rear of body
          • big hindquarters
          • long tail (acts as counterbalance)

      3. Swimming
        1. amphibious (semiaquatic)
          • thick fur
          • webbed feet (used for propulsion)
          • tail may be flattened, provides stability and propulsion
        2. aquatic
          • fore and hind limbs modified into flippers for propulsion
          • thick layer of subcutaneous fat (blubber)
          • basically no externally visible tail
        3. marine (fully aquatic)
          • fusion of cervical vertebrae
          • forelimbs modified into flippers (provides stability)
          • elimination of hind limbs and most of pelvic girdle (not visible externally, but remnant bones may remain)
          • tail flattened dorso-ventrally into a fluke (provides propulsion)
          • thick layer of subcutaneous fat (blubber)

      4. Gliding and Flying (volant)
        • Characterized by a patagium (membrane)
        • Gliding has evolved independently at least 5 times in marsupials, rodents and dermopterans


      5. Climbing (arboreal, scansorial)
        1. Claws
        2. Prehensility
          • Usually associated with larger body size relative to substrate
          • Occurs in hands, feet, tail
          • Associated with loss of claws (nails instead)
          • Asociated with friction pads
        3. Suspensory (hanging)
          • Associated with long, curved digits
          • Associated with fusion of cervical vertebrae

      6. Digging and burrowing (fossorial)
        • Usually dig with forelimbs, but sometimes with incisor teeth (e.g., mole rats)
        • Large claws
        • Short, broad forelimbs (if forelimbs are used for digging)
        • Forelimbs splayed to the sides (if forelimbs are used for digging)
        • More vibrissae than terrestrial mammals, in more locations on the body
        • Small eyes
        • Often lack pinnae