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Evolution of Birds
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Dinosaurian, Avialae, Differences, Selection and Speciation, Hybridization.
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BirdsWeek 2
Chris Foster
Bird Origins
Dinosaurian [raptor] features shared with birds;
1. Furcula and sternum
2. Thin scapulae [shoulder blade]
3. Pneumatic bones
4. Semi-lunate carpal [more flexible, fused bone in both/ birds part of the bones fold
back/ in birds the ischium is fused to the pubis
5. Reduced wing digits
6. Posteriorly inclined pubis
7. Tarsometatarsal leg bone in non-avian dinos fused ankle and metatarsals = tibiotarsus
[fused tibia and tarsals]
8. Feathers
9. Uncinate process [hooked shape]
Avialae; the first of the flying dinosaurs;
- 4 digit hand / hollow bones [furcula-wishbone = rigidity] / hollow cylindrical
feathers/ tufted feathers / semi-lunate carpal for flexibility = folded wing / closed
feathers, asymmetrical / long limbs/ toothless beak, short feathered tail.
Evolution;
a. Simple filament-like “protofeathers” found on head of compsognathid
sinosauropteryx
b. Increasing branches varied feathers form a wing on the arms of dromaeosaurid
Zhenyuanlong Suni
c. Parent oviraptorosaur brooding nest with large eggs
d. Furcula [wishbone] of dromaeosaurid Bambiraptor feinbergorum
e. Hollow/ internal cavity in tibia of tyrannosaurid Alioramus altai
f. Pneumatic foramina – air sacs penetrated bones in cervical vertebrate and ribs of
tyrannosaurid Alioramus altai
g. Reconstructed brain of troodontid zanabaza junior [olfactory bulb/ telecephalon/
cerebellum/ midbrain/ hindbrain
Key differences with birds;
1. Brain – cerebral hemi
2. Fused digits
3. Synsacrum [fused lower vertebrate] increased strength and lightweight
4. Pygostyle, less vertebrates and fused – rectrices [increased tail feathers attach]
5. Keel sternum; larger area for flight muscles attachment – pectoralis muscle
6. Uncinate process; hooks provide strength to rib cage, provide muscular
attachment
7. Brain case; remodeling and lightening of the jaw = toothless
Feathered Dinosaurs modern birds;
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