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Topic 8: Appendicular Skeleton

� What makes up the appendicular skeleton?

� What is the pattern of serial homology of the limbs?

� Tetrapod front limb morphology

� Tetrapod hind limb morphology

� How do the limbs develop?

� What patterns of evolution have limbs undergone?

� Transition from water to land

� What are some specializations of the limbs?

Divisions of the Skeleton:

Liem et al. Fig. 8-15, 8-18; Dean 1895

� Cranial

� Postcranial

� Axial

� Appendicular

What are the components of

the appendicular skeleton?

Appendicular Components

� _____________� Multiple elements

� In body proper

� _____________� Single long bone

� _____________� Two long bones

� _____________� Many bones

� How have these bones developed?

Modified from Liem et al. Fig. 9-7

Appendicular Components

� Girdle� Variable elements (see later)

� Stylopodium� Humerus

� Femur

� Zeugopodium� Radius & Ulna

� Tibia & Fibula

� Autopodium� Carpals, Metacarpals & Phalanges

� Tarsals, Metatarsals & Phalanges

Liem et al. Fig. 9-10, 9-11

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Limb Development

� Starts with formation of ______________

� What germ layers are involved?

© P Martin; ncbi.nlm.nih.gov

Limb Development

© E Uthman; BioDes; cmrb.eu

� Early formation of ___________ ________________ (AER)

� Zone of cell proliferation

� Zone of differentiation

� Proximal structures develop first

� Zone of _______________ (ZPA)

� Expresses Sonic Hedgehog to define digit polarity

Limb Development

� Fibroblast Growth Factor (FGF)

� Induces AER formation

� Proliferation of Mesoderm

� Formation of digits

� Bone Morphogenetic Protein (BMP)

� Involved in apoptosis

� Noggin gene

� Blocks apoptosis

© BioDes

Limb Development

� Limb element identity

� _____________ expression patterns

� Slight differences between front and hind limbs

Hall, Fig. 7-4

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Limb Development

� Solid line indicates limb axis

� Gene expression data inform us about homology

� Are tetrapod digits homologous to radials or are they neomorphs?

Liem et al. Focus 9-1

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� Front limb differentiation

� Addition of elements

� Increased _____________

of elements

� Evolution of ___________

Liem et al. Fig. 9-5, 9-6, 9-8

Front Limb & Pectoral

Girdle Evolution

Liem et al. Fig. 9-5, 9-9, 9-11

Front Limb & Pectoral

Girdle Evolution

Mammal

� ______________

� Cleithrum, supracleithrum,

interclavicle lost

� Clavicle remains

� ______________

� Scapula and coracoidincrease in size

� Coracoid lost in mammals

� What has happened in terms of what

elements are

involved?

Front Limb & Pectoral Girdle Evolution

Basal Amphibian

Benton 1997 pg 183; Benton Fig 4-2a; Pough et al 2004 Fig 2-2

Panderichthys

Bony Fish

� Separation of front limb &

girdle from the head skeleton

� Why?

Hind Limb Evolution

Liem et al. Fig. 9-4, 9-6, 9-10; Hall 4-3

� Very similar to front limb evolution� Evolution of autopodium

� Evolution of digits

� Increased robustnesss

Pelvic Girdle Evolution

� How does this differ

developmentally from the pectoral girdle?

� Bones are conserved in

position

� _________

� _________

� _________

Liem et al. Fig. 9-4, 9-9, 9-11

Mammal

Pelvic Girdle Evolution

Benton 1997 Fig 3.22; Pough et al 2004 Fig 2-2a

Acanthostega

Protopterus

(African lungfish)

� Transition in articulation of pelvic girdle

� Fishes: ______________

� Tetrapods: solidly articulated with vertebral column

� Why?

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Evolution of Limbs

Transition from water to land

What are the

functional reasons for

each change?

Terrestrial

Obligate Aquatic

What morphological

changes are involved

in this evolutionary

transition?

Evolution of Limbs

What are the

functional reasons for

each change?

What morphological

changes are involved

in this evolutionary

transition?

� �

So, how does the function of front & hind limbs differ?

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Specialization of the Limbs

� Limbs to Fins

� Shortening of stylopodium & zeugopodium

� __________________

� Fusion of digits (not phalanges)

Storrs, 1993

Specialization of the Limbs - Wings

� Digits 1-3 reduced

� Phalanges in digit 4 elongated

� Metacarpal 4 elongated

Liem et al. Fig. 9-12

________ _____ ____

� Loss of digits 1 & 5

� Digits 2-4 reduced

� Carpometacarpus

� Elongation of radius & ulna

� Phalanges & metacarpals in digits

2-5 elongated

� Digit 1 reduced

� Radius elongated

� Ulna reduced

Limb Specializations

� Limb posture and cursoriality

� ______________

� ______________

� ______________

� Fusion of tibia & fibula

� Elongation and fusion of metatarsals

� Fusion of phalanges

& loss of digits

� How does this

improve speed?

� What species have each posture?

© UMMZ

Limb Specializations

� A dog at full gallop with long strides

Liem et al. Fig. 9-14

Limb Specializations

� Human skeletal

adaptations for endurance running

� Narrow waist

� Large vertebral centra

� Relatively short _______

� Large _______________

� Long _______________

� Spring-like ___________

� Short ______________

� Relatively ___________

After Lieberman et al. 2009