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Lecture 2

The Skeleton & the Pentadactyl Limb
Support & locomotion -

Supports weight against gravity

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Reinforced by action of muscles

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Divided into unit for movement

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Variations (Bipedal, quadrupedal, swimming, flying)
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Large store of Ca

The skeleton is broken down into 3 parts
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All Vertebrates have a consistent skeletal structure
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Most have limbs
and girdles
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Bone Structure:
Cortical= Hard, compact, long bones
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Ossification: The process of creating
bone
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Primitive fish
are mostly cartilage, whereas
mammals are mostly bone
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Skull: Complex and fossilised skulls show lot of variation
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The bones are the same, but have enlarged or reduced for different functions and
degrees of complexity
...
”
Fish= Large olfactory centres correspond to great sense of smell
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Birds= Large cerebral hemispheres reflect the increase in stereotypic behaviour such as courtship and nest
building
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The Lower Jaw: In first land vertebrates there were 4-6 bones
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Teeth: Have evolved from uniform homodont dentition found in fish and reptiles to specialised teeth in
mammals
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Omnivores have all of these
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The Spine: Relatively standard in all vertebrates
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Teleost fish= Well ossified vertebrae, notochord persists within each centrum
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Hemal arches in caudal vertebrae
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Pentadactyl limb= The five fingered structure of limbs in vertebrates
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Biserial fins= Central axis of bone or cartilage with a series of radial bones
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Found in
lungfish, precursor of tetrapods
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No basal lobe, no skeletal elements within the fin other than radials
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Have basal cartilages and a row of distal cartilages
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Some tetrapods
have lost one or both pairs of appendages
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Forelimbs only (manatees, cetaceans,
manatees, dugongs, salamanders)
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Front/upper limb: The humerus varies little in the tetrapods
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Bird’s wing= Birds only have 3 digits
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Bat’s Wing= Metacarpals and the last four phalanges become greatly elongated to support the wing
membrane
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Lecture 2

Terrestrial locomotion=
Sprawling: Most primitive posture
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Well-suited to exploiting lateral undulations of the torso for locomotor force
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Function in behaviours other than simple walking
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Requires less robust limb skeleton, locomotor force derives
mostly from muscles that move the limb directly
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Digigrade= First digit reduced or lost, weight on metacarpals
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Modifications for grasping= Some mammals can flex the joint between the palm and the base of the fingers
(rodents)
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Opposable
thumb found in primates but mostly developed in humans
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In land vertebrates these bones
are modified into the bones of the middle ear
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Os cordis- found between the ventricles of deer/bovines
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Os clitoridis- clitoris of otters and some rodents/rabbits
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Rostral bone- pig’s snout



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