Teeth High energetic costs associated with higher body T; increased selective pressure for efficient...

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!