Exam 1: Evolution of Flight

150 million years ago

• went from a reptilian ancestor into feathered birds

• not great flyers

• first diversified in the mesozoic

• diversified more in the tertiary

  • more modern taxa

extinctions

• Class Aves was in several extinctions

  • late cretaceous

  • pre-pleistocene ice ages

    • 25% of existing birds lost

birds as reptiles: commonalities (5)

• skull holds a lot of the similarities

• similar leg structure

• scales

  • feather are modified scales

  • scales are on bird legs

• females are heterogametic

• nucleated red blood cells

birds skulls as compared to reptiles

• lower jaw composed on several bones

• ring that supports the eye

• single middle ear bone

• single occipital condyle

• lower jaw articulated on quadrate bone

• expanded lateral brain case

archaeopteryx

• the original link between birds and reptiles

• a find so good that people thought it was fake

• came out briefly after Origin of Species

• found in fine-grained limestone in central europe

  • late jurassic

• first evidence was a single feather

• that cool as skeleton was found, second

• feathers are indistinguishable from modern feathers

Newer fossil finds

• seven specimens

• Crow-sized, bipedal ‘reptile’

• Blunt snout, many small teeth

• Feathers on wings and tail (probably entire body as well)

• Capable of gliding, weak flapping

• Feather veins were asymmetric

  • Indication of flight

archaeopteryx as a intermediate

• similar features

  • skeletal, brain, inner ear

• brain 3x larger than comparable reptiles

  • smaller than modern birds, birds have much larger brain than reptiles

  • larger visual centers

    • good for hanging out in the air

  • neural system for flight

• heavy skull

  • boney, teeth

  • enhances inner ear structure

• has claws 

• long, boney tail

• overall, heavy for a bird

birds as dinosaurs

• the line of evolution is debated

  • thecodonts vs theropods 

    • theropods is the more accepted opinion

    • are related to trex

birds as dinosaurs - sinornis santensis

• china 1987

• toothed cretaceous fossil

• sparrow sized

• halfway point between ancient and modern

• many intermediate features between Archaopteryx and modern birds

  • Strong hand, forearm, and pectoral girdle modifications

    • bones are starting to fuse

    • rigidity of the skeleton

  • Raise wing over body

  • Large pygostyle –tail support

    • goodbye tail bone!

  • Opposable rear toe

    • good for perching

birds as dinosours - feather development

• birds are in fact related to t-rexes

  • fully feathered dinosaurs 

  • onset of downy feathers

  • good for thermoregulation