Evolutionary origin of birds

Question 1

Which extant group was thought to be the origin of birds?

Answer 1

**The ratites **
However, more recent evidence suggests this is not the case
→The ratites are a polyphyletic group where flightlessness co-evolved independently

Question 2

What is the most widley accepted hypothesis for the origin of birds?

Answer 2

Thomas Huxley: Evolved from Theropods
(share a common ancestor: Dromaeosaurs raptorrrr)

Question 3

Describe the Dromaeosaurs

Answer 3

• Very diverse
• Modification of forelimb to be flexible
• Had a seizing function - unique
• Some had feathers (Not for flight but for insulation or sexual selection)

Question 4

Birds have ____ dinosaur skulls

Answer 4

paedomorphic

Question 5

List some bird-like features of Dinosaurs

Answer 5

• Egg laying
• Scales (feathers are derived scales)
• S-shaped neck
• Tridactyl foot
• Bipedal
• Wishbone (Theropods)
• Fused sternum (Theropods)

Question 6

Describe the reptilian features of the Archaeopteryx

Answer 6

Strong thick bones
No fusion of vertebrae
Toothed jaw

Question 7

Describe the bird features of the Archaeopteryx

Answer 7

• Well developed feathers
• 3 fingers (reduction in digits)
• S shaped neck
• Hind-foot → Morphology similar to extant birds
• Furcula → fused clavicles similar to extant birds

Question 8

Describe Archaeoptryx’s feathers and what this suggests

Answer 8

• Asymmetrical (typical of flight feathers)
• Had a moulting pattern to falcons to maximise feathers for flying
  = suggests capable of flight
• Primitive shoulder limited its flapping ability
• Probably lived in areas without trees, so could glide