Teeth•High energetic costs associated with higher body T; increased selective pressure for efficient food processing
•Mammal teeth---modified & specialized to far greater extent than in any other group of vertebrates
•Slice, dice, puncture, stab, grind, defend, display,....
•Teeth alone often indicative of diet
•Variable BETWEEN major lineages, relatively constant WITHIN species
•FOSSILIZE; may fossil species described from teeth alone, often a SINGLE TOOTH!
•Traditionally given heavy emphasis in inferring relationships, BUT often misleading due to convergence, etc.
gumline
Crown
Root
Alveolus (pl. “alveoli”)
Enamel: hardest tissue in mammals. 3% organic... “pre-fossilized”
Pulp cavity: nerves & vessels. Remains open in rootless, ever- growing teeth (rodent incisors, some cheekteeth)
Dentine: same mineral composition, but 30% organic; softer.
Cementum: bony material surrounding root
Teeth grow from one of 3 bones
Tooth replacement•Living mammals DIPHYODONT (EXCEPT molars!). Ancestral condition for mammals. Mostother vertebrates have POLYPHYODONT dentition.
•“Deciduous” teeth replaced by “permanent” teeth.
•Replacement timing varies (e.g., shrews)
•Morphology often different in deciduous teeth vs. permanent teeth
•Sequence of replacement constant w/in species: useful for AGING
dC1
Canine
canine
•First tooth in maxilla or at maxillary/premaxillary suture.
•All mammals have AT MOST one canine per quadrant
•Usually single-cusped (unicuspid), single-rooted (but exceptions)
•Generally used for stabbing, holding prey in carnivores (but exceptions)
•Often absent (rodents, some artiodactyls) or heavily modified (elephants)
•Can be problematic to identify if absent and next tooth is caniniform
Premolars
premolars
•Posterior to canines, rooted entirely in maxilla
•Variable: tiny, peglike in some, massive crushing tool in others
•Often “molariform,” but generally smaller, less developed than molars
•Premolars are replaced, molars aren’t
Premolars
premolars
Dog carnassialpair
Molars
molars
•Posteriormost teeth in toothrow
•Variable, but late to erupt
•Erupt anterior-to-posterior
•NOT REPLACED!
Cheekteeth
molarspremolars
“cheekteeth”
Despite variation in I, C, much of the important functional variation is found in CHEEKTEETH, particularly MOLARS.
“Assembly line” for food processing
capture, pick up
puncture
puncture, sheargrind gulp!
“Convergence” within dental arcade:
Elk
Sea otter
Philippine treeshrew
“caniniform” incisor
“incisiform” canine
“molariform” premolar
Primitive dental formula
Marsupial:
I C P M =4433
11
44
33
I C P M =5054
11
33
44
Placental:
BUT 1st premolar (P1/p1) lost in many living placentals, so maximumoften 3 premolars!!!!!!!
Primitive dental formula
I C P M ==4433
11
44
33
Placental:
1111
P1 absent in MOST, but not ALL, living placental mammal
Evolution of molars
Mammals of Triassic (early) mammals..................... “shearing” action.
3 prominent cusps.cingulum
Upper:
Lower:
(compare withearly mammal)
stylar shelf(expanded cingulum)
“Tribosphenic” molar pattern
Modifications of the tribosphenic molar
Quadritubercular or Quadrate or Euthemorphic
tribosphenic
quadritubercular
Modifications of the tribosphenic molar
Quadritubercular or Quadrate or Euthemorphicstylar shelf
(addition of 4th major cusp)
Dilambdodont
Crests connecting two prominent outer coneswith smaller cones (“-styles”) of stylar shelfform double-V or W-shape.
(addition of 4th major cusp)
Zalambdodont = cusps form single V.
(Stylar shelf is incorrectly labeled on this figure!)
Zalambdodont
parastylemesostyle
LOSS of metacone, metastyle.
Omnivores•Quadritubercular•Bunodont (ROUNDED)•Brachydont (LOW-CROWNED)
Herbivores
Brachydont vs. hypsidont
Lophodont (herbivores)
hypocone
protocone
paracone
metacone
anterior
labial
Carnassial pair (carnivores)
P4
M1
protocone
paracone
metacone
anterior
labial
Carnassial pair
“Assembly line” for food processing
capture, pick up
puncture
puncture, sheargrind gulp!