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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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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.