Class Aves - Diapsid amniotes

9000 species

Characteristics in General

1. feathers -

2. forelimbs modified to wings

3. hindlimbs modified for walking, perching, swimming

4. horny beaks

5. lay eggs

Archaeopteryx

thecodont teeth - set in sockets like crocs

long bony tail and clawed fingers like reptiles

abdominal ribs

Other similarities of birds and reptiles:

1. single occipital condyle

2. single middle ear bone - the stapes

3. 5-6 bones in lower jaw

4. excrete uric acid

5. similar eggs

Two groups of birds:

1. Ratite -

2. Carinate -

Adaptations for flight:

1. feathers

a. Contour feathers

b. Down feathers

c. Filoplume feathers

Feathers - epidermal; keratin

2. Skeleton

- light, sturdy

- pneumatized bones

- skull highly specialized; mostly fused into one piece

- toothless

- rigid vertebral column; most vertebrae fused together and with pelvic girdle

- ribs fused with vertebrae, pectoral girdle and sternum

- large keel on sternum

- limbbones fused and reduced in number

3. Muscles

- muscle mass located near center of body; even leg muscle mass close to body - use tendons to distribute force

- pectoralis

Food and Feeding in Birds:

No teeth but Beaks strongly adapted to specialized food habits

Short Pharynx - Muscular Esophagus (many with crop)

Proventriculus - gastric juices (chemical)

Stomach

Gizzard - muscular for grinding food (mechanical)

Ceca -

Intestines end in cloaca - common chamber for digestive, genital ducts and ureters (from kidneys).

Circulatory System:

- Four chambered heart (like mammals); right aortic arch leads to the dorsal aorta in birds - left in mammals.

- Nucleated red blood cells (mammals enucleate)

Respiratory System:

- Parabronchi - air continually flows. One way flow of air

In amphibians, reptiles and mammals - tidal flow (bidirectional)

- Air sacs in thorax and abdomen that connect to lungs

Excretory System:

- Large paired metanephric kidneys - thousands of nephrons

- ureters drain kidneys to cloaca -

- Uric acid (like reptiles) Salt glands near eyes

Nervous System:

1. well developed cerebral hemispheres

2. cerebellum -

3. Midbrain -

Eyes -

rods (for dim light) -

cones (for color and acuity) -

Evolution of Flight:

Why Fly? Two Hypotheses

- food source 1. flapped from ground to air

- escape predation 2. glided from high places

- dispersal

Feathers arose for thermoregulation and secondarily for flight.

Reproductive System:

- Male birds produce sperm in testes and store sperm in a seminal vesicle = enlarged distal end of vas deferens.

- air sacs help cool testes

- most birds have no copulatory organ - cloacal kiss

ducks and geese have a penis

- Female birds - only left ovary and oviduct develop

- Eggs ovulated from ovary -----> infundibulum -----> oviduct -----> obtain albumin from special glands -------> shelled by shell gland

Mating Systems:

Monogamy - 90% of birds

Polygamy

Polygyny most common