Chapter 2  - teeth and diet

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TEETH

  1. Much of the adaptive success of mammals is related to teeth
  2. Mammals are the only vertebrates that masticate
  3. Mammalian teeth are adapted for various diets
  4. Note the relationship between dentition and feeding pattern and how this impacts shape and structure of jaw and associated musculature [temporal, masseter, and pterygoid muscles]
  5. mammalian fossil record is typically teeth (and isolated jaws) 
  6. Learn more about teeth from the University of Michigan's Museum of Zoology
  7. Teeth from UT Arlington, Comparative Vertebrate Anatomy, Dr. Jonathan Campbell
Tooth Structure
  1. thecodont (rooted)
    1. gomphodont: multiple roots
    2. alveolus (-i): socket(s)
  2. parts (Fig. 4.17)
    1. crown--above the alveolus
    2. root--in alveolus, below the gum line
  3. composition (Fig. 4.17)
    1. enamel--outer layer 97% hydroxyapatite, 3% organics [ectodermal]
    2. dentine--inner layer, 70% hydroxyapatite, 30% organics [dermal]
    3. cementum--spongy, bone-like material; holds tooth to socket;
    4. pulp cavity--within the dentine, holds blood vessels and nerves.

 

image courtesy of BIODIDAC

  Kinds of teeth

  1. only mammals have differentiated (heterodont) teeth
    1. incisors-anterior-most teeth [uppers occur on premaxilla]
    2. canines--longer, conical teeth used for grasping
    3. cheek teeth--post canine
      1. premolars--cheekteeth that have deciduous predecessors (milk dentition)
        1. molariform teeth, squarish teeth used for grinding food
      2. molars--cheekteeth that do not have deciduous predecessors
  2. NOTE that some mammals have homodont dentitions.
  3. edentulous (edentate - without permanent teeth)

Replacement

  1. typically mammals are diphyodont--have a single deciduous milk dentition
  2. some are polyphyodont--have multiple replacement sets (Trichechidae-30+ molars)
  3. toothed whales are monophyodont--have only a single set
  4. Most tooth replacement is vertical.
  5. Trichechids and Elephantidae have horizontal tooth replacement [Fig. 18.4]

Dental formulae [Fig. 4.20]

teeth are listed in the order they occur in the jaw; upper jaw listed over lower

e.g., 3/2 1/1 4/4 3/3 = 44 total teeth
e.g., 1/1 0/0 4/4 3/3 indicates no canines
P3 or P3 indicates the third lower or upper premolars
p3 and P3 indicates the third lower and third upper premolars
1/1 0/0 5/4 means the post-canine teeth are lumped together

Primitive dental formula

Dental anomalies

  1. supernumerary teeth
  2. agenesis

Evolution of multicusped tooth pattern (cheek teeth)

  1. triconodonts have three linearly arranged cusps (Fig. 4.9A)
  2. evolution of triangular, multicusped cheek-teeth in the symmetrodonts improved transverse shearing action by increasing the surface area of tooth
  3. tribosphenic tooth (Fig. 4.10)
    1. evolved in primitive therians with the evolution of the neomorph protocone and talonid
    2. characteristic of primitive (arthropodophagous) marsupials and placentals
    3. upper molars with three prominent cusps
      1. trigon--triangle formed by the paracone, metacone, and protocone: the apex of triangle on lingual side
    4. lower molars with three prominent cusps (trigonid) plus basin (talonid)
      1. trigonid--a triangle formed by the paraconid, metaconid, and the labial protoconid
      2. talonid--a posterior extension of lower tooth that accommodates the protocone. contains entoconid, hypoconid, and hypoconulid.
    5. specialized independent occlusal functions
      1. points puncture
      2. crests shear
      3. protocone and talonid function together to crush and grind

Modifications of the Tribosphenic Pattern

  1. many mammals have a square molariform tooth
    1. results from the addition of the hypocone to the trigon (=euthemorphic)
  2. Modifications of euthemorphic produce a variety of cusp patterns  [Fig. 4.18]
    1. quadritubercular--4 main cusps (e.g. humans, pigs) that are
    2. typically, bunodont--hemispherical cusps
    3. lophodont--occlusal surface of lophs (ridges), that typically run the width of the tooth
    4. selenodont-- crescent-shaped lophs
    5. fusion of two or more cusps to form a cutting edge.
      1. sectorial dentition (secodont)-occlusal surface has shearing or cutting edge.
      2. carnassial teeth--shearing teeth, have blade-like (sectorial) scissors action [Fig. 4.19A].  In the Order Carnivora they are always P4 and m1.
  3. Some other terms
    1. brachyodont--low crowned teeth, e.g. sheep;
      1. always closed-rooted; wear with age
    2. hypsodont--high crowned teeth, e.g. horses
      1. can be open rooted and ever-growing
    3. diastema--gap in the tooth row [Fig. 4.19B]

Structure of the lower jaw [Fig. 4.19]: mandibular condyle and muscle groups  in

  1. carnivores
    • condyle at the same level as tooth row, scissors-like occlusion, temporalis is the main muscle
    • image courtesy of BIODIDAC

 
  1. herbivores:
    • condyle above the level of tooth row, occlusion of cheek teeth at same time, masseter is the main muscle
    • image courtesy of BIODIDAC

 

 

FEEDING ADAPTATIONS:

  1. Herbivore
    1. Grazer
    2. Browser
    3. Folivore
    4. Frugivore.
    5. Nectivore
    6. Granivore
  2. Carnivore
    1. Sarcophage 
    2. piscivore
    3. molluscivore
  3. Omnivore
  4. Insectivore
    1. myrmecophage
      1. convergence in anteaters [Fig. 26.11]
  5. Sanguivore
  6. Filter feeder (Planktivore)

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