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Lecture 8

Lecture 8.docx

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Shawn Lehman

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ANT333 Lecture #8 – Dietary Adaptations: Dentition I Enamel  Hardest biological structure in body: varying from 5-8 on Mohs scale (talc =1, diamond = 10).  Attains full thickness before teeth emerge into oral cavity.  Composed of inorganic calcium phosphate.  Thicker over cusps of unworn premolars and molars, thinner around cervical region.  Deciduous teeth have thinner enamel than permanent teeth.  Basic histological structure in mammals is calcified rods or prisms. Dentine  Not as mineralized as enamel, so softer than enamel but harder than bone.  Makes up most of tooth and root.  Composed of collagen and hydroxyhapitite.  More compressible and elastic than enamel – absorbs force placed on tooth  Does not contain variable histological patterns; thus, not of taxanomic utility for scientists. Heterodonty  Teeth that are regionally differentiated in form so as to serve special functions. Four Kinds of Teeth: 1. Incisors  Blade-like teeth that cut and shear food at the front of mouth.  Upper incisors are limited to the premaxilla bone.  Incisors are relatively small, simple teeth in most primates.  Some primate lineages have enlarged (plesiadapiformes) and/or specialized incisors, such as the tooth combs of lemurs. 2. Canines  Large teeth at corners of mouth, distal to incisors, that can pierce food and whose relative size important to social structure of many groups of primates.  Upper canine is first tooth immediately behind suture between premaxilla and maxilla.  Lower canine is tooth immediately in front of upper canine when upper and lower jaws occluded (brought together). 3. Premolars  Intermediate in form between canines and molars; commonly have two cusps (raised points on the crown) so referred to as bicuspids.  Often thickened ring of enamel around base of crown called the cingulum.  In some primates, particularly OW Monkeys, anterior premolar acts as honing (sharpening) stone to sharpen posterior edge of the upper canine when two teeth come into contact (sectorial premolar). 4. Molars  Have expanded occlusal surface, with more cusps than premolars, for crushing and grinding food.  Upper molars of primates all derive from a tritubercular (triangular-cusp) pattern.  Crown of each tritubercular tooth has three main cusps 1). Protocone, 2). Metacone and 3). Paracone 1 Basic Dental Structure  Trigon – set of three major cusps – increases surface area  Earliest therian mammals had upper teeth with 3 cusps arranged in triangle, with base running along labial edge of tooth.  In upper jaw, cusp at apex of triangle (on lingual side) termed protocone; anterior cusp along labial margin is paracone; and posterior cusp along same margin is metacone. Basic Dental Structure  Teeth had substantial stylar shelf (labial to paracone and metacone), which contained several smaller cusps (styles). Set of 3 major cusps is called trigon.  Lower teeth contain a trigon (called trigonid), but triangle of cusps is turned around.  Protoconid is labial whereas paraconid and metaconid on lingual side.  Low shelf, called talonid or talonid basin, develops at posterior end of tooth.  Talonid basin ringed by three cusps: labial hypoconid, lingual entoconid, and between them, the hypoconulid. Evolution of Tooth Structure  The teeth of living placentals believed to evolved from tribosphenic teeth.  In tribosphenic teeth of upper jaw, three main cusps are protocone, paracone, and metacone.  Ridge called a cingulum connects main cusps.  Small shelf named stylar shelf runs along labial (lip) side of tooth. On it are located several smaller cusps (parastyle and others). Evolution of Quadritubercular Dentition  Early in mammalian history addition of 4th main cusp, hypocone, to upper molar.
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