Chapter 2

Question 1

What are birds descended from?

Answer 1

• theropod dinosaurs!

Question 2

What are features shared by birds and reptiles?

Answer 2

• similar lower jaw
• single bone in the middle ear
• singular occipital condyle
• a sclerotic eye ring
• scales on legs (similar to reptile scales)
• nucleated red blood cells
• ## an amniotic egg

Question 3

Describe the similar lower jaw of birds and reptiles

Answer 3

• lower jaw made up of several bones fused together
• the angular, surangular, articular, coronoid, and dentary

Question 4

Describe the single bone in the middle ear that birds and reptiles share

Answer 4

• stapes (or columella)

Question 5

What does the single occipital condyle do?

Answer 5

• joins the skull and the first neck vertebrae

Question 6

Describe the Theropod Hypothesis

Answer 6

• birds evolved from a particular group of theropod dinosaurs
• mostly closely related to the dromaeosaurs
• evidence supporting this include traits shared by both birds and theropods

Question 7

Traits shared by birds and theropods

Answer 7

• lightweight bones: hollow, thin-walled
• bipedal
• thin scapula
• 5+ vertebrae incorporated into sacrum
• large orbits
• S-shaped curved neck
• loss of digits (five)
• flexible wrist
• furcula
• hindlimb
• pubic boot

Question 8

Describe the flexible Wrist shared by birds and Theropods

Answer 8

• • 3-fingered opposable grasping manus (hand) shared by Archaeopteryx and Deinonychus
• 3rd digits showing similar unusual length
• shared moon-shaped wrist bone between theropods, the semilunate carpal
• believed these bones fused to form carpometacarpus in ancestor of living birds

Question 9

Describe the hindlimb shared by birds and theropods

Answer 9

• have elongated metatarsals
• hinge-like ankle joint
• 4-toed pes(foot) supported by 3 main toes

Question 10

Archosaurs

Answer 10

• one of 2 major clades of diapsid reptiles
• includes Crocidillians and Pterosaurs
  (crocodiles and birds!)

Question 11

2 major clades of dinosaurs

Answer 11

• Ornithischians and Saurischians

Question 12

What are the two arrangements of pelvic bones found in dinosaurs?

Answer 12

• both made up of Ilium, Ischium, and pubis
• Ornithischian pelvis (pubis and ischium pressed against the other)
• Saurischian pelvis(ischium and pubis pushed apart)

Question 13

Maniraptora

Answer 13

• includes therizinosaurs and alvaresaurs, oviraptors, troodontids, dromaeosaurs,
  scansoriopterygids, and the Aviale
• these groups have shown evidence to have downlike filamentous(fuzzy) and/or advanced vaned feathers

Question 14

Aviale

Answer 14

• modern birds and their direct ancestors

Question 15

Which groups in this chapter have just filamentous feathers present?

Answer 15

• Ornithomimosauria
• Compsognathidae
• Tyrannosauroidea

Question 16

Describe the general evolution of feathers in regard to this chapter

Answer 16

• hypothesized to be an adaptation for flight, but fossil review reveals the complex, vaned feathers existed before origin of birds and the origin of flight in theropod dinosuars
• ancient theropod feathers included downlike filamentous(fuzzy) and advanced, vaned feathers

Question 17

Pygostalia

Answer 17

• occurence in early cretaceous period
• branching includes the loss of tail vertebrae and fusion of the last few vertebrae at the tip of the tail into a new structure: the pygostyle
• tail feathers insert on the pygostyle

Question 18

Ornithothoraces

Answer 18

• clade that includes the 2 major Mesozoic avian clades: Enantiornithes and Ornithuromorpha
• dominated mesozoic avian evolution

Question 19

Enantiornithes

Answer 19

• shared many traits with today living birds(keeled sternum, coracoid bone)
• has scapula fossa and coracoid process

Question 20

Scapula fossa

Answer 20

• fossa refers to a depression or hollow usually into a bone (scapula for this)

Question 21

Coracoid process

Answer 21

• small, hook-like structure on the lateral end of the superior anterior portion of the scapula
• the long coracoid rasied the shoulder joint, creating space for a tendon used in modern flight upstroke

Question 22

Neornithes

Answer 22

• under Ornithuromorpha!
• Found in late cretaceous period
  has a scapula process and coracoid fossa (depression or hollow into the bone)
• shares relationship with enantiornithes

Question 23

Example species of enantiornithes

Answer 23

• Sinornis, Nanantius

Question 24

Examples of Neornithes

Answer 24

-Ichthyornis(toothlike, ternlike birds), Hesperornis(aquatic, toothed seabirds; foot-prepelled diving birds)
(under Ornithurines in Neornithes)

Question 25

Ornithuromorpha

Answer 25

-found in early cretaceous period
- sister group to Enantiornithes
- includes Neornithes
- gave rise to modern birds
- derived feature of unicate process on ribs, added stability to the upper rib cage and aid in flying and respiration

Question 26

Describe features of Ornithuromorpha seen to be like modern birds

Answer 26

• wading birds
• diving birds
• perching birds
• secondary flightless terrestrial type birds

Question 27

Describe the reptile vs. avian characteristics of Archaeopteryx

Answer 27

• reptilian characteristics include a toothed beak, wing glaw, and long tail with many vertebrae
• the avian characteristic is airfoil wing with contour feathers