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Bird Emergence from Dinosaurs (Dinosaur-Bird Transition (Gradual…
Bird Emergence from Dinosaurs
Gradual Evolution
Most features evolved for reason other than flight
Hinge-like ankle
Bipedal posture
(walk on hind legs only)
Simple filamentous
feathers
Wishbone
(furcula)
Vaned feathers formed quills
Wings
Lost tail (fused)
Larger chest
muscles
to stabilise shoulder
free forelimbs to do other things
Stepwise changes in one dino lineage morphology lead to bird evolution
No significant difference btwn dinosaurs & birds
Statistical tests for morphological variability
Find no significant separation btwn bird & closest dino relatives
Dinosaur-Bird Transition
Gradual transition
with stepwise dinosaur morphology changes
Smaller body
Lost tail/teeth
Reduced claws
Bigger brain
Lengthened / bigger wings
True Birds
Bird evolved from dinosaurs which developed ability to actively flap wings
Bird body plan result of stepwise changes in dino morphology
Preserved alongside feathered dinosaurs
in Chinese volcano deposits
Rate of Evolution
Evolution rate varies
btwn different parts of family trees (phylogeny)
over time
Once bird body plan assembled from dinosaurs
Very fast evolution
Greater on dino lineage leading to birds than others
Evolutionary potential unlocked causing pulse
Dinosaur morphology change
Gradual & stepwise evolution toward flight
Evolution rate acquired from
Constraining how long branch on phylogeny alive
from fossils
Observing morphological changes
Gives rate
Birds are dinos!
Only dinosaurs that survived End-Cretaceous
Unknown why no other dinos survived
Most birds died & few survivors could radiate?
Major modern bird groups
evolved after major dino extinction
Over 10 thousand bird species today