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Lecture 6

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Shawn Lehman

ANT 333 Lecture #6 – Locomotor Adaptations Locomotor Adaptations  Found in many parts of body.  Most differences in anatomy of limbs & trunk of living primates clearly related to differences in locomotor & postural abilities  Locomotion and posture also effect orientation of head on trunk, shape of thorax, & positioning of abdominal viscera.  Posture correlated with diet – e.g. foraging Skeletal Morphology & Phylogeny  Modifications of musculoskeletal system related to locomotor differences influenced by ancestry of group being considered.  Primates often evolved different solutions to the same problem.  Thus quadrupedal lemurs, quadrupedal monkeys, and quadrupedal apes show similarities related to their quadrupedal habits, but they show affinities to other lemurs, monkeys, and apes as well.  Bones can provide information about both phylogeny & adaptation if two can be accurately distinguished.  Best approach is to examine mechanical problems that different types of locomotion present.  Consider how living primate species have evolved musculoskeletal differences to meet these mechanical demands.  Phylogeny has a large effect on morphology Skeletal Adaptations  Concentrate on features of skeleton that can be related to different postures and methods of progression  Important to realize that such “correlations” between bony morphology and locomotor behavior are constantly being tested and refined by experimental studies (which we will cover in later lectures). Arboreal Quadrupedalism  Balancing an lowering centre of gravity  Push limbs away from centre (abduction) to get lower  Reduce lateral sway General Anatomical Characteristics of Arboreal Quadruped  Long tail for balancing  Narrow Thorax  Deep ulna  Grasping foot  Laterally placed scapula  Lateral olecranon Key Anatomical Features of Arboreal Quadruped  On distal end of humerus, medial epicondyle is large and directed medially  Olecranon process of the ulna is long  Olecranon fossa of the humerus is shallow  Ulna shaft is relatively robust and often more bowed and deep in arboreal quadrupeds than in many other locomotor types. Key Morphological Features of Arboreal Quadruped 1  Most distinctive features of hindlimb joints of arboreal quadruped reflect characteristic abducted posture of that limb  Femoral neck set at moderately high angle relative to shaft, enhancing abduction at hip.  At knee, abduction (away from midline) of hindlimb expressed in asymmetrical size of femoral condyles & their articulating facets on top of tibia.  Femur points outward Key Morphological Features of Arboreal Quadruped  At ankle, tibio-talar joint also asymmetrical.  Lateral margin of proximal talar surface higher than medial margin, reflecting normally inverted posture of grasping foot.  Arboreal quadrupeds all have large hallux (big toe) & moderately long digits.  Foot is rotated Anatomical Characteristics of Terrestrial Quadruped - Reduced tail – don’t need for balance - Narrow thorax - Short digits - Posteriorly extend olecranon process - Restricted shoulder joint - Robust radius Key Anatomical Features of Terrestrial Quadruped  Articulating surfaces of scapula and head of humerus provide only limited anterior-posterior motion.  Greater tuberosity of humerus is high and positioned in front of shoulder.  Medial epicondyle on humerus is short and directed posteriorly  Articulation of ulna with humerus is relatively narrow  Head of radius is relatively large, oval in shape, and flattened proximally. Key Anatomical Features of Terrestrial Quadruped  Olecranon process extends dorsally to long axis of ulna  Olecranon fossa on posterior surface of humerus is deep  Joints kept close into the body Vertical Clinging & Leaping  Uses tail to rotate in air  Hind-limb propulsion, hind-limb landing Anatomical Characteristics of a Leaper - Narrow tibia - Short femoral neck Key Morphological Features of Leaping Primates  In strepsirhines that normally leap from vertical clinging posture, ischium usually extended posteriorly rather than distally.  This anatomy increases moment arm of hamstrings when limb near full extension, which is common situation for vertical clingers.  Ischium usually pointed towards back  Should be a gliding motion Key Morphological Features of Leaping Primates 2  Hip extension major source of propulsive force in leaping.  Thus, primate leapers usually have long ischium, which increases leverage of hamstring muscles.  Minimize lateral and medial locomotion Key Morphological Features of Leaping Primates  Arboreal quadrupeds use abducte
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