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Lecture 9

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Shawn Lehman

ANT333 Lecture #9 – Dietary Adaptations: Dentition II We will Cover Three (3) Aspects of so-called (only looking at morphology) Dietary Adaptations: 1. Molar shearing crests, 2. Diet and enamel thickness, & 3. Food handling and incisor structure. Shearing Crests  Richard Kay (1984) devised a ‘‘shearing quotient’’ (SQ), a measure of relative shear potential (how well it “cuts”) of a tooth.  First, lengths of mesiodistally running crests connecting main cusps of lower second molars are summed.  Least-squares regression line (comparing to variables – dependent vs independent – what is X doing to Y) is fit to frugivorous extant species in logarithmic space with  mesiodistal occlusal surface length as independent variable and summed crest length as dependent variable.  Log transformed in order to make data fit parameters Shearing Crests  Frugivorous (bench mark) species alone are used to control for allometric changes in animals with similar adaptations.  SQs are computed as deviations from the frugivore regression; that is, as measures of differences between observed and ‘‘ex pected’’ shearing crest lengths for a given tooth length.  Higher the SQ, the relatively longer the crests. Shearing Crests  Kay’s results demonstrate that folivores & insectivores have higher SQs than frugivores.  Among frugivores, hard-object specialists have lower SQs than softfruit eaters, indicating that the former have extremely blunt teeth designed for crushing.  Relationship between SQ and diet holds for all major extant primate groups: strepsirrhines, platyrrhines, cercopithecoids, and hominoids. Diet and Shearing Quotients in West African Lorises SQ = (observed summed shearing – expected summed shearing)/expected summed shearing *100 Diet and Shearing Quotients in African Monkeys  Folivores & insectivores have higher SQs than frugivores  Among frugivores, hard-object specialists have lower SQs than soft fruit eaters; former have extremely blunt teeth designed for crushing Diet and Enamel Thickness  Among extant species, some of thickest enamel is in mangabeys (Cercocebus), orangutans (Pongo), brown capuchins (Cebus apella), & the pithecines.  Peccaries, which have low-cusped teeth, are capable of cracking open hard nuts.  Kiltie ( 1979) reports that some of these nuts require sustained loads of more than 1000 kg per square inch before cracking. 1 Diet and Enamel Thickness  Simons & Pilbeam (1972) suggested thick enamel adaptation for terrestrial primates eating tough, grit-laden abrasive foods.  Thick enamel needed to prevent excessive wear. Thus, originally, thick enamel associated with terrestrial diet.  Kay (1981) noted that terrestrial forms DO NOT have thicker enamel than arboreal forms. He suggested thick enamel adaptation to withstand cracking & splintering during crushing of hard foods. Diet and Enamel Thickness  Primates with thick enamel often crack open & eat contents of extremely hard nuts  Primates with large molars also tend to have thick enamel  Strong negative correlation between relative enamel thickness & relative shearing crest development in cercopithecoids  Thicker enamel = shorter the length of shearing crest Diet and Enamel Thickness  Thin molar enamel is rapidly perforated by dental wear  Relatively softer, more rapidly wearing dentin appears in enamel windows apices of tall, sharp, principal molar cusps  Raised edges of worn enamel on crest margins form sharp edges that facilitate shredding and slicing during mastication  Worn down enamel create more striated patterns that create sharp edges Diet and Enamel Thickness  Molar system emphasizing high cusps & thin enamel associated with leaf-eating diet  Maximal food shredding is needed because leaves contain large quantities of structural carbohydrate: digestion is greatly facilitated by more effective reduction of particle size  Species with poorly developed molar shearing crests have relatively thicker enamel Diet and Enamel Thickness  This dental structure may be adaptive response to selection for more uniform distribution of very high occlusal forces engendered while masticating hard, tough food objects  Poorly developed shearing crests lead to a reduced ability to subdivide food particles maximally, which in turn results in a drop-off in the digestibility of structural carbohydrates Pitheciines: Pithecia, Chiropotes, & Cacajao  Want fruit when unripe and only want seeds o Avoid competition Fruit Terminology  Pericarp: wall of a fruit; encloses seeds & is derived from ovary wall. In fleshy fruits, pericarp is typically made up of three distinct layers. 1. Exocarp: forms tough outer skin of fruit, e.g., orange peel 2. Mesocarp: is often fleshy and forms the middle layers. 3. Endocarp:
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