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Lecture 7

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Shawn Lehman

ANT 333 Lecture #7 – Prehensile Tails & Suspension in Primates Grasping Appendages  Evolution of grasping hands & feet & a divergent hallux bearing flattened nail occurred early in primate evolution -+  Initial changes in primate prehension were associated with exploitation of food resources such as ripe fruits, floral nectar, & mobile insect prey located on small, flexible supports  Hold branch between 2 and 3 digits Prehensile Tail  Prehensile tail functions as 5th limb & enables animal to suspend its full body weight supported by tail alone, or to use tail in conjunction with 1 or more limbs to suspend & maintain balance in an arboreal setting  Increases stabilization, frees up hands and feet Prehensile Tails in Tropical Mammals - Tree kangaroo - Tamandua - Possum - Golden Anteater  Convergent evolution, no common ancestor with prehensile tail Evolution of Prehensile Tail  A small set of New World primate genera (Ateles, Alouatta, Cebus, Brachyteles, & Lagothrix) possess a prehensile or grasping tail Evolution of Prehensile Tails in Primates  Based on genetic & anatomical evidence, prehensile tails evolved twice in platyrrhine evolution: once in common ancestor of atelines (Alouatta, Ateles, Brachyteles, & Lagothrix) & again in lineage leading to Cebus  Because these taxa have not shared common ancestor for ca. 20 million years, prehensile tail of Cebus & atelines best interpreted as parallel evolutionary adaptations  Prehensile tail primates have heavier tails and variable tail lengths Tail Use During Feeding  Used their tail as an anchor during above-branch feeding activities in which the hindlimbs were positioned on stable supports & forelimbs positioned well in front of the body  Active flexion of caudal musculature played an important role in supporting much of animals’ body weight  Tail prevents downward motion, curls up when not needed Feeding Sphere & Tail Use  Tail plus hindlimbs prehensile postures extend capuchin’s feeding sphere enabling forager to utilize more extensive set of small branches from which to feed.  Tail used as anchor or counterbalance during certain above-branch feeding activities on relatively stable supports. Comparisons of tail-use among Ateles, Wooly Monkeys, & Alouatta  Tail use in all species of Ateles has been closely linked to forelimb suspensory locomotion (arm swinging or brachiation) as a specialized mode of travel  Lagothrix and Brachyteles frequently employ tail-assisted forelimb suspensory locomotion during travel, as well as tail-assisted forelimb suspensory postures during feeding 1 Comparisons of tail-use among Ateles, Wooly Monkeys, & Alouatta  In all studies of howler positional behavior, tail reported to play a more frequent weight-bearing role during feeding then during traveling . Mostly about foraging Summary  Behavioral evidence for Cebus, Alouatta, and Ateles consistent with suggestion that prehensile tail plays important role in feeding ecology, posture, and locomotion.  Differences in tail and vertebral morphology, and positional behavior among genera, however, suggest that platyrrhine prehensile tail has come to serve related but different functions in each taxa  Prehensile tail of Alouatta moderately elongate & lumbar region of vertebral column is less reduced than Ateles, Brachyteles, & Lagothrix  Cebus possesses relatively short & fully-haired prehensile tail  Frequent use o
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