8/19/2013. Topic 14: Body support & locomotion. What structures are used for locomotion? What structures are used for locomotion?

Transcription

1 Topic 4: Body support & locomotion What are components of locomotion? What structures are used for locomotion? How does locomotion happen? Forces Lever systems What is the difference between performance and kinematics? What structures are used for locomotion? Structures for locomotion Walking/running Digging What are the various modes of locomotion? In water On land In the air Photos PJB, National Geographic, G Nafiz, KP Bergmann What structures are used for locomotion? Structures for locomotion What structures are used for locomotion? Structures for locomotion Crawling/slithering Enhancing stride length Gliding Photos J & C Sohns, S Zankl Photos T Laman, PJB

2 How does locomotion happen? How does locomotion happen? Newton s three laws : A body in motion will remain in motion unless a force acts on it & vice versa 2: Force = mass x acceleration F = ma 3: For every action there is an equal and opposite reaction Locomotion is the result of the This occurs with all substrates and in many situations JF Alward Forces produced during locomotion Animal s muscles exert a force F on substrate Substrate exerts a reaction force, R, equal & opposite to F R is often called a R R can be broken down into: P Forward component V Vertical component opposite to L P components also exist L V Pough et al. 2004, Fig 0- F How does locomotion happen? More on lever systems Lever systems A lever is a rigid bar that pivots about a fulcrum Each lever has 2 lever arms, length L i, length L o Each lever arm has a force associated with it, F i, F o Force is exerted on the inlever, and produced at the out-lever F i x L i = F o x L o Same in-force Same in-lever + out-lever What do the diagrams below tell us? F i L i L o F i L i L o Classified by relative position of parts st Class: Fulcrum between in & out lever 2 nd Class: Out-lever in the middle 3 rd Class: In-lever in the middle Pough et al. 2004, Fig 0-3b Pough et al. 2004, Fig 0-3 2

3 More on lever systems A B Fulcrum In-lever Out-lever C D E Pough et al. 2004, Fig 0-3

4 How are performance & kinematics different? How are performance & kinematics different? A measure of how good something is at doing something In locomotion, there are several measures of performance Sprint speed Power output A measure of how something is done In locomotion: Stride frequency Limb angles Can be very detailed Kinematics and performance are related Sprint speed = stride length X stride frequency Morphology can be closely related to kinematics Hind limb length in lizards is proportional to stride length DJ Irschick Plot: Irschick & Jayne 999; Diagram: PJB What are the various modes of locomotion? Aquatic: Used by elongate herps Serpentes, Gymnophiona, Sirenidae, Amphiumidae Many strong swimmers are not that elongate Iguana, Amblyrhychus, Basiliscus, Physignathus, Crocodylia Involves the body and tail If limbs are present, they are folded back against body Undulations increase in caudally Modes of locomotion Aquatic: Anura Simultaneous with hind limbs Body is held rigid Each propulsive kick counteracts drag from the water Testudines Trionychidae: with all four webbed limbs Cheloniidae: Simultaneous of flippers Lift and propulsion generated with up & down stroke of front limbs Steer with hind limbs Photo T De Roy; Pough et al. 2004, Fig 0-7 Pough et al. 2004, Fig 0-9, Photos:?? Modes of locomotion Terrestrial Most terrestrial locomotion involves Many exceptions In general Amphibia and Reptiles have a Limbs oriented laterally as opposed to parasagittally (like mammals) Crocodylia and Chamaeleonidae have a more erect posture There are many ways to determine gait Generally include Sequence of foot falls Number of limbs in contact with the ground (min & max) Relative speed Limbs have more air time with Running animals often have no contact with the ground at some point in stride cycle Photos PJB, KP Bergmann, A Britton Pough et al. 2004, Fig 0-2

5 Gaits are often poorly defined in sprawling vertebrates Many locomotor specializations of limbs exist in Varanus exanthematicus Enhances stride length Leads to higher velocity Crocodylus johnstoni Can More upright posture Often only two feet on the ground is an asymmetrical gait A Britton Pough et al. 2004, Fig 0-5 and high speed Bipedal lizards tend to have: Long Muscles proximally on hind limbs: Speed vs. Force Short front limbs Long tails (counterbalance) Some high speed species move on fluid substrates : Basiliscus : Uma, Callisaurus Often additional adaptations for this: Toe fringes on posterior edge of toe Bipedalism is associated with high speed in lizards May be high speed Even non-bipedal lizards sometimes run bipedally Irschick and Jayne 999 Photos:??, KE Bonine, PJB Anura, lizards Specializations (mainly Anura) Rigid, light body Long hind limbs Short, rounded ilium Allows rotation of body to control jumping angle Competing aspects of a good jump Increased weight decreases velocity, distance and height Toro et al. 2004; National Geographic 2

6 Modes of locomotion Jumping Tail plays a role in lizard jumping Anolis carolinensis The body axis is responsible for pushing on substrate Involves complex musculature, with some muscles crossing multiple joints in snakes Simpler set of muscles in lizards Gillis et al Pough et al. 2004, Fig 0-7 F forward F object F lateral Limbless lizards and snakes move differently Limbless lizards all use simple undulation Snakes have a large repertoire of modes of movement Lateral undulation Horizontal waves travel down body objects in the environment Posterior and lateral force components Slide-pushing Similar to lateral undulation, but: Very fast undulations F object F lateral F forward Photo PJB Pough et al. 2004, Fig 0-, 0-2 Rectilinear locomotion Involves bilateral waves of Costocutaneous muscles move skin relative to body wall Movement is in a straight line Can see waves of muscle contraction along body Concertina Slow, energetically expensive Localized body bends are made and then straightened Use in Pough et al. 2004, Fig 0-5 PJB; Pough et al. 2004, Fig 0-3

7 Sidewinding Fossorial specializations Specialized locomotion for: Snake pushes vertically down on substrate Sections of the body are: Crotalus cerastes Lifted Moved forward Placed back down Limblessness Often involves structures to force way through substrate in Bipes with front limbs Amphisbaenia have a skull that can be used for digging Generally only two points of contact with substrate Pough et al. 2004, Fig 0-4 Pough et al. 2004, Fig 0-2, www. Digimorph.org Fossoriality Skin can move relative to the body Body can thin or thicken to burrow Pointed skull drives through substrate Clinging Claws Undulations under a loose substrate Limbs folded along body Often used as a defense to escape from a predator PJB; Pough et al. 2004, Fig 0-20 Gekkonidae, Diplodactylidae, Anolis, Prasinohaema Involves elaborations of scales called setae (seta) Adhesion by intermolecular forces: van der Waals forces Many Anura Have adhesive discs on digits Capillary adhesion Water on the structure is needed Pough et al. 2004, Fig 0-25; KP Bergmann 2

8 Aerial locomotion No amphibians or reptiles have powered flight Involves jumping off a high place and spreading of patagia Difference between falling, parachuting and gliding is the amount of LIFT relative to DRAG The more lift, the lower the angle of descent, the more gliding the descent is Pough et al. 2004, Fig 0-27 Aerial locomotion Gliding has evolved several times independently in Borneo Distance between trees > in many other parts of the world Chrysopelea, Draco, Rhacophorus, Ptychozoon Photos T Laman