The aves

Question 1

How many species of bird are there?

Answer 1

Approx. 10,000

Question 2

The birds are one of the most diverse vertebrates clades, second only to the…?

Answer 2

Teleosts

Question 3

Which group were the birds descended from?

Answer 3

Saurischian theropod dinosaurs.

Question 4

What were the feathers of a) Alverezaurid and b) Caudipteryx like?

Answer 4

a) Filamentous proto-feathers

b) Had large feathery tail plumes

Question 5

It was thought feathers first evolved for what purpose?

Answer 5

Thermoregulation or display, not flight.

Question 6

What was microraptor?

Answer 6

A dromeosaur from China, was fully arboreal with true feathers.

Question 7

Archaeopteryx was the intermediate between theropods and birds. What time period was it from?

Answer 7

Late Jurassic.

Question 8

Archaeopteryx was the intermediate between theropods and birds. What were its a) theropod and b) bird-like features?

Answer 8

a) Long tail, teeth and claws

b) Forelimbs with feathers, beak-like structure

Question 9

What was Vagavis?

Answer 9

A neornithine from the late Cretaceous. This is the group containing modern birds.

Question 10

Birds originate from the late Cretaceous. When did they diversify?

Answer 10

The Cenozoic.

Question 11

List 3 synapomorphies of theropods and birds.

Answer 11

1. 3 digits
2. Half-moon shaped carpal bone
3. Furculae

Question 12

a) Theropods and b) birds both have 3 digits, but different 3 digits. Which ones have they both retained?

Answer 12

a) Thumb, index and middle

b) Middle 3 digits

Question 13

What is a ‘half-moon shaped carpal bone’?

Answer 13

Wrist bone: reduces drag and allows birds to move their wings in a ‘figure of 8’ motion.

Question 14

Define the furculae.

Answer 14

Fused clavicles (collar bones), form the characteristic ‘wish-bone’.

Question 15

What are the furculae used for in modern birds?

Answer 15

Flight muscle attachment.

Question 16

List 10 synapomorphies of modern aves.

Answer 16

1. Backwards-facing first toe
2. 3 digits
3. Elongated metatarsals
4. Large, keeled sternum
5. Keratinous beaks
6. No true teeth
7. Enlarged furculum
8. Enlarged sacrum
9. Pygosytle
10. Short femur and longer lower-leg bones

Question 17

Why do birds have a backwards-facing first toe?

Answer 17

To grip branches.

Question 18

Describe the arrangement of the digits in the wing.

Answer 18

The first digit sticks up like a little spur. The second digit is the alula. The third digit is the main wing-bearing bone.

Question 19

Define the alula.

Answer 19

A bone that prevents stalling at high angles of attack.

Question 20

Why have birds lengthened their metatarsals?

Answer 20

Most species adopt a digigrade stance.

Question 21

What is the sternum for?

Answer 21

Flight muscle attachment.

Question 22

Why is the sacrum enlarged?

Answer 22

Provides stability when landing on hard surfaces if the pelvis is strongly joined to the thoracic skeleton.

Question 23

Define the pygostyle.

Answer 23

Fused caudal vertebrae to support the tail feathers and flight muscles. Helps to control flight.

Question 24

Why do birds have a short femur and elongated lower leg?

Answer 24

Allows more mobility in the knee region.

Question 25

How are a) bird legs different to b) theropod legs?

Answer 25

a) Birds have a short femur and elongated lower leg
b) Theropods have a long femur and shortened lower leg (for powered running)

They are opposites.

Question 26

What are the 2 hypotheses for the origin of flight?

Answer 26

1. Cursorial, ground-up

2. Arboreal, tree-down

Question 27

Explain the cursorial hypothesis for the origin of flight.

Answer 27

Birds evolved from fast-running terrestrial theropods that leapt onto prey.
Running leaps became gliding leaps became flying leaps.

Question 28

Give support for the cursorial hypothesis.

Answer 28

Theropods were active terrestrial predators and not arboreal.

Question 29

Explain the arboreal hypothesis for the origin of flight.

Answer 29

Small, arboreal theropods hopped frombranch to branch and began to extend these to gliding jumps.

Question 30

What do both hypotheses rely on?

Answer 30

Extended feather filaments that facilitated gliding.

Question 31

There are 2 models to explain the origin of flight. They can be applied to both hypotheses. What are the models?

Answer 31

1. Pouncing pro-avis model

2. Running up trees model

Question 32

Explain the pouncing pro-avis model.

Answer 32

Feathers acted as parachutes to slow the rate of descent.

Question 33

In the pouncing pro-avis model, in what situations might feathers be needed as parachutes?

Answer 33

1. For predator evasion

2. For jumping onto prey

Question 34

Where would the feathers need to be positioned in order to create drag-based lift, as in the pouncing pro-avis model?

Answer 34

At the end of their limbs.

Question 35

Where would the feathers need to be positioned in order to create thrust-based lift?

Answer 35

Close to the body.

Question 36

Explain the running-up-trees model.

Answer 36

Birds ran up the side of trees whilst flapping their wings to create thrust. Once in the tree they would again need their feather to get back down.

Question 37

What support can be found in modern birds for the running-up-trees model?

Answer 37

Juvenile birds do it to evade predators.

Question 38

In a feather, what is the rachis?

Answer 38

A central vein.

Question 39

In a feather, why are the filaments coming off the rachis covered in hooks?

Answer 39

To ensure a continuous flight surface, all the filaments hook together.

Question 40

What kind of keratin do a) birds and b) mammals have?

Answer 40

a) Keratin A

b) Keratin B

Question 41

The earliest feathers were symmetrical. What does this tell us about their function?

Answer 41

They were not used for powered flight. May have been good parachutes.

Question 42

Why is it that symmetrical feathers do not allow flight?

Answer 42

A thrust vector operating on a central rachis causes the feathers to twist 90 degrees, meaning it is unable to trap air.

Question 43

Thus what are flight feathers like?

Answer 43

Asymmetrical: a thrust vector cannot twist the feather if the rachis is off-centre, creating resistance for the wings to push against.