Archaeopteryx

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Archaeopteryx

• One of first bird fossils described (1861)
• Still the earliest known bird
• Lived 145 MYA
• Missing link between birds and reptiles,
  prominent in early debates about evolution
  (Origin of Species published 1859)

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Avian Features

• Feathers (asymmetric)
• Wing-like forelimb
• Hallux
• Furcula

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Reptilian Features

• Teeth instead of bill (not as critical as one
  might think)
• Claws on forelimb
• Tail with vertebrae
• No keel
• No reinforced ribs

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Archaeopteryx lived in the middle of the age of
dinosaurs, before Tyrannosaurus rex, before
flowering plants
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4 Lines of Reptilian Evolution

• Turtles
• Aquatic reptiles (extinct)
• Mammal line
• Lizards/snakes thecodonts

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Thecodont radiation

• Armored dinosaurs (Ornithischia) (extinct)
• Flying reptiles (Pterosaurs) (extinct)
• Crocodiles
• Sauropods (extinct)
• Theropods (extinct)
• Carnosaurs
• Coelurosaurs

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Classic theory birds evolved from thecodonts

• Crocodile link rejected
• Long period with no fossil forms (80 MY)
• Arboreal origin flight
• Leaping
• Parachuting
• Gliding
• Feathers flight first, insulation second

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Ostrom theory birds evolved from coelurosaurs

• Group appeared 155 MYA (too late?)
• Extreme convergence of skeletal features
• Cursorial origin of flight
• Balance
• maneouver
• Feathers insulation first, flight second
• Dinosaurs as endotherms