CLASS AVES (BIRDS)Chapter 18 p. 344-367

Overview• About 9,700 described species

• Largest of land vertebrates, only fishes have more

• Great diversity in size, diet, and habitats

Evolution of Birds• Believed to be direct descendents of reptiles (branch of dinosaurs)

• Famous fossil specimen: Archaeopteryx “ancient wing”• Found in quarry in southern Germany, 1861• Dated at 150 mya• Characteristics of both birds and reptiles

Archaeopteryx• Reptile-like:

• Long tail• Teeth in beak• Wings with claws

• Bird-like:• Beak• Long, flexible neck• Feathered wings• Warm blooded?

Bird Characteristics

• Feathers and wings

• Scales on legs

• Bones light

• Sternum has keel

• 4 chambered heart

• Syrinx (voice box) calls for mating, warning,

protection, territories

Bird Characteristics

• No bladder (semisolid urine)

• Females have one ovary and oviduct

• Internal fertilization (amniotic egg)

• Warm blooded (endothermic)

• Behavior patterns

• Parental care, nest building, courtship,

migration, attachment of mates

Skeleton• Bone

• Pneumatic• Hollow to reduce weight

and increase strength• Skull

• Kinetic• Lighter than mammalian

skull• Legs heavier to increase

center of gravity

Skeleton• Keeled sternum

• Allows for pectoralis muscle attachment (used for flight)

Digestion• Voracious eaters

• High metabolic rate• Anatomy

• Esophagus• Crop• Stomach

• Proventriculus• Gizzard

• Paired ceca• cloaca

Respiration• Most efficient respiratory system of any vertebrate

• Two respiratory cycles for one gasp of air