Text Questions: Chp 2, 4, 5

Question 1

Birds are “reptiles” and therefore have a number of skeletal features that distinguish them from mammals. Describe how these features differ: occipital condyle; middle ear, lower jaw; ankle joint.

Answer 1

-Birds have one occipital condyle, mammals have two
-Middle ear: Birds/reptiles have one, mammals have three (two evolved from lower jaw bone)
-Lower Jaw: Birds/reptiles have three bones, mammals have one
Ankle joint: Birds/reptiles ankle located in middle of foot or tarsal bones. Mammals ankle is between long lower leg bones (tibia) and tarsi

Question 2

What anatomical and behavioral characteristics indicate that, among extant (living) vertebrates, birds are most closely related to crocodilians (e.g., alligators and crocodiles)?

Answer 2

• Both are archosaurs and have anteorbital fenestra.

- Both developed extensive prenatal care behavior

Question 3

Identify avian and “reptilian” features of Archaeopteryx.

Answer 3

Archaeopteryx:

• Avian features: Hallux, feathers on wing, tail, body, asymmetrical feathers, capable of gliding/leaping (but not long, sustained flight-lacked birdlike shoulder joint)
• Reptilian: Gastralia (free belly ribs), teeth, tail was long and boney

Question 4

Analysis of the theropod dinosaur origin of birds documents that the rate of evolutionary change was quite gradual. Describe how the following characters changed from common ancestors, theropods to birds; du toes, pubis, clavicle, hand.

Answer 4

• Fifth toe was lost
• First toe pointed backward (hallux) (Avialae)
• Hips: long pubis bone evolved pubis boot, which later points backward
• Clavicle fused to form furcula (in theropods)
• Hand: Outer two digits were reduced. 4 and 5 were lost
• Pneumatic bones (air filled bones)
• Wrist: crescent shaped bone formed by fusion of carpals (semilunate carpal), then fused to become carpometacarpus
• Feathers!

Question 5

Which characteristics of the Enantiornithes were similar to Archaeopteryx and which were more similar to modern birds?

Answer 5

Modern birds:

• Coracoid (fossa/scapula process for articulation)
• Fusion of tarsometatarsus

Archaeopteryx:
-Teeth

Question 6

Describe, BRIEFLY, the diversity of size, the ecology, and geographic distribution of these birds. Are they ancestors to any living birds?

Answer 6

Enantiornithes:

• Crow to vulture size
• None survived, End of Mesozoic extinction, but sister group=Ornithurae

Ornithurae :(uncinate processes derived character) gave rise to modern day birds
- Range of size and lifestyles; similar to modern wading birds, perching, diving, and flightless terrestrial forms
-

Question 7

The phylogeny of Mesozoic birds indicates that the flight morphology and flight capacity of modern birds evolved in a series of incremental steps. Identify and describe how flight morphology advanced in the following groups: Avialae, Pygostylia, Ornithurae, Aves.

Answer 7

Avialae-reversed hallux, unserrated teeth, <25 tail vertebrae

-Tarsometatarsus

Pygostylia-Carpometacarpus, tail <8 free vertebrae, pygostyle, pubic boot lost

-Keeled sternum, strut like coracoid, modern hummerus, alula

Ornithurae-Ribs with uncinate process

Aves-loss of teeth

Question 8

It was long presumed that feathers evolved from scales. Based on the information in Chapter 2 as well as on pp 82-84 (Chapter 4), explain the current “Evo-Devo” hypothesis about the origin of feathers? What evidence (from living birds and from fossils) support this? What might have been the adaptive function of the early stages of feathers?

Answer 8

• Feather development informs evolution
• Complex growth process=series of stages
• Each stage characterized by new development
• 5 distinct phases
• Each stage found in modern birds, feather follicles capable of producing hypothesized morphologies
• Molecular evidence