Elements of appendicular skeleton: f li b

Elements of appendicular skeleton: f li bforelimbforelimb

Pectoral girdle: Pectoral girdle:

Forelimb: Forelimb:F mF m

MammalsMammalsAnterior Posterior

Li b d i t d l Li b d i t d l Limbs and associated muscles are Limbs and associated muscles are derived from somatic hypomere:derived from somatic hypomere:

Hox gene expression in:Hox gene expression in:Hox gene expression in:Hox gene expression in:

Bony fishesBony fishes TetrapodsTetrapods

Pectoral girdlePectoral girdle

Modifications of Modifications of the basic fish the basic fish

pattern in pattern in vertebratesvertebrates

AnteriorAnterior

EndochondralDermal

elements

AnteriorAnterior

Endochondralelements

elements

Shark

Medial viewMedial view

Lateral viewLateral view

Tiktaalik Tiktaalik rosaerosae

Sarcopterygian. Sarcopterygian. Shallow-water fish, but with:

Robust pectoral limbs, functional wrist Well-supported ribs

Shallow-water fish, but with: Robust pectoral limbs, functional wrist Well-supported ribs Functional neck Functional neck

Pentadactyl forelimb structure:Pentadactyl forelimb structure:

Hallux

Number of digits in Number of digits in l hibi l hibi

Digits reduced in Digits reduced in living amphibiansliving amphibians

early amphibians early amphibians initially variedinitially varied

from 4from 4--1313

Theropods

Convergent evolution Convergent evolution of external forms of external forms of external forms of external forms

using differentusing differentcombinations of combinations of

skeletal elementsskeletal elementsskeletal elementsskeletal elements

Historical constraints on adaptationHistorical constraints on adaptationE Gi d h bE Gi d h b Ex: Giant pandas thumb: Pandas related to bears and raccoons

(Carnivora).

Ex: Giant pandas thumb: Pandas related to bears and raccoons

(Carnivora). Bears /raccoons are the most omnivorous

carnivores. Use front paws to manipulate food.

Bears /raccoons are the most omnivorous carnivores.

Use front paws to manipulate food.p p Giant panda are more dexterous than bears

and raccoons. Diet restricted to bamboo.

p p Giant panda are more dexterous than bears

and raccoons. Diet restricted to bamboo. Strip leaves between flexible thumb and

other digits. Problems:

Strip leaves between flexible thumb and other digits.

Problems: Primates have opposable thumbs, not

carnivores. 5 (not 4) remaining digits.

Primates have opposable thumbs, not carnivores.

5 (not 4) remaining digits.g g

Constraints on adaptationConstraints on adaptationP d th bP d th b Pandas thumb: Enlarged carpal bone:

Bears: slightly enlarged radial

Pandas thumb: Enlarged carpal bone:

Bears: slightly enlarged radial Bears: slightly enlarged radial sesamoid bone.

Carnivores: two 1st-digit abductor muscles

Bears: slightly enlarged radial sesamoid bone.

Carnivores: two 1st-digit abductor musclesmuscles.

In bears, one muscle attaches instead to radial sesamoid.Abd t d dd t l

muscles. In bears, one muscle attaches

instead to radial sesamoid.Abd t d dd t l Abductor and adductor muscles are modified 1st-digit abductors.

Pandas thumb is modification of

Abductor and adductor muscles are modified 1st-digit abductors.

Pandas thumb is modification of carpal structures.carpal structures.

Limb Limb

Amphibian and Amphibian and

configurationsconfigurations

Amphibian and Amphibian and reptilian reptilian

conditioncondition(2 ff ti (2 ff ti (2 effective (2 effective

limb segments)limb segments)

Mammalian and Mammalian and archosaur archosaur

diti diti condition condition (3 effective (3 effective

limb segments)limb segments)gg

Muscular sling Muscular sling Muscular sling Muscular sling of mammalsof mammals

Elements of appendicular skeleton: hi dli b

Elements of appendicular skeleton: hi dli bhindlimbhindlimb

Pelvic girdle Pelvic girdlePelvic girdlePelvic girdle

Hindlimb Hindlimb Hindlimb Hindlimb

MammalsMammalsAnterior Posterior

Anterior Posterior

Acanthostega : One of first amphibians with well defined digits (8)

Acanthostega : One of first amphibians with well defined digits (8) One of first amphibians with well-defined digits (8)

on forelimbs, hindlimbs. Limbs extended laterally, not ventrally.

One of first amphibians with well-defined digits (8) on forelimbs, hindlimbs.

Limbs extended laterally, not ventrally. Joints (elbow, wrist, knee, ankle) present but with

little mobility. Joints (elbow, wrist, knee, ankle) present but with

little mobility.

Sues footSues foot((Tyrannosaurus rexTyrannosaurus rex))

TheropodTheropodTheropodTheropodfeet (4 toes)feet (4 toes) UtahraptorUtahraptor

VultureVulture

Hallux

H l iH l iHuman pelvisHuman pelvis

Human pelvisHuman pelvis

Knee

ElbowWrist

Ankle

Models of limb evolutionModels of limb evolutionModels of limb evolutionModels of limb evolution

A t f t j t iti A t f t j t iti Account for two major transitions in chordate limbs:

Account for two major transitions in chordate limbs: Aquatic fin folds to fins.

Fin-fold theory. Aquatic fin folds to fins.

Fin-fold theory. Fins to tetrapod limbs.

Axial and basal models. Fins to tetrapod limbs.

Axial and basal models.

Cephalochordate condition

FinFin--fold fold hh

condition

theorytheory

Fish conditionFish condition

Fin-fold modelFin-fold modelFin-fold modelFin-fold model

Models of limb evolutionModels of limb evolutionModels of limb evolutionModels of limb evolution

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Gnathostomata

Osteichthyes

Vertebrata

B l d lB l d lBasal modelBasal model

Axial modelAxial modelAxial modelAxial model

Axial modelAxial modelAxial modelAxial model

Lungfish condition is plesiomorphic. Axial bones homologous with Lungfish condition is plesiomorphic. Axial bones homologous with g

posterior long bones + carpals + metacarpals + phalanges.

gposterior long bones + carpals + metacarpals + phalanges.p p g

Evidence: embryonic and gene expression patterns of vertebrate

p p g Evidence: embryonic and gene

expression patterns of vertebrate expression patterns of vertebrate limb development.expression patterns of vertebrate limb development.

inductive sequenceinductive sequence

Basal modelBasal modelBasal modelBasal model

Coelacanth (crossopterygian) Coelacanth (crossopterygian) Coelacanth (crossopterygian) condition is plesiomorphic.L b h l ith b l

Coelacanth (crossopterygian) condition is plesiomorphic.L b h l ith b l Long bones are homologous with basal fin elements (heterochronic change).

Long bones are homologous with basal fin elements (heterochronic change).

Radials are homologous with carpals + metacarpals + phalanges.

Radials are homologous with carpals + metacarpals + phalanges.

Supported by phylogenetic evidence for monophyly of the sarcopterygians.

Supported by phylogenetic evidence for monophyly of the sarcopterygians.f p y y f p ygf p y y f p yg

Context of evolution of tetrapod limbContext of evolution of tetrapod limb Late Silurian Devonian (410-400 mybp):

Diversification of plants into semi-aquatic and terrestrial habitats.

Late Silurian Devonian (410-400 mybp): Diversification of plants into semi-aquatic and terrestrial

habitats. Formation of wetlands and rivers with abundant plant

life. Appearance of terrestrial insects.

Formation of wetlands and rivers with abundant plant life.

Appearance of terrestrial insects.

Transition from fin to limb preceded that from aquatic to terrestrial habitats.

Transition from fin to limb preceded that from aquatic to terrestrial habitats. Early limbs sufficient for shallow, muddy waters. Multiple, clearly defined digits. Weak girdles and limbs weak wrists

Early limbs sufficient for shallow, muddy waters. Multiple, clearly defined digits. Weak girdles and limbs weak wristsWeak girdles and limbs, weak wrists.

Tetrapods: reduction of dermal bone, elaboration of endochondral elements

Weak girdles and limbs, weak wrists.

Tetrapods: reduction of dermal bone, elaboration of endochondral elementsendochondral elements.endochondral elements.

Structure of the vertebrate skeletonStructure of the vertebrate skeleton Two major sections:

Axial skeleton Appendicular skeleton

Two major sections: Axial skeleton Appendicular skeleton

Heterotopic elements Heterotopic elements

Articulations Articulations

Some heterotopic elementsSome heterotopic elements

P i b lPenis bacula

Structure of the vertebrate skeletonStructure of the vertebrate skeletonStructure of the vertebrate skeletonStructure of the vertebrate skeleton Two major sections:

A i l k l t Two major sections:

A i l k l t Axial skeleton Appendicular skeleton Axial skeleton Appendicular skeleton

Heterotopic elements Heterotopic elements

Articulations (arthroses): Articulations (arthroses):

SynarthrosesSynarthroses

AmphiarthrosesAmphiarthroses

DiarthrosesDiarthroses

(forming meniscus layers)

Femoral ballFemoral ball--andand--socket socket

jointjoint

Trends in the skeletal systemTrends in the skeletal systemyy Internalization: from external dermal skeleton to

internal endochondral skeleton. Internalization: from external dermal skeleton to

internal endochondral skeleton. Differentiation of regions of the skull and axial

skeleton.C h li i i d d f h d f

Differentiation of regions of the skull and axial skeleton.C h li i i d d f h d f Cephalization: independence of head from postcranial skeleton.

Development and specialization of pentadactyl

Cephalization: independence of head from postcranial skeleton.

Development and specialization of pentadactylDevelopment and specialization of pentadactyllimbs.

Relocation of limbs from lateral to ventral.

Development and specialization of pentadactyllimbs.

Relocation of limbs from lateral to ventral. Interlocking of vertebrae via zygapophyses. Reduction (loss and fusion) of skeletal elements. Interlocking of vertebrae via zygapophyses. Reduction (loss and fusion) of skeletal elements.