Chapter 42Birds

Section 1

Origin & Evolution of Birds

Characteristics• Feathers- composed of keratin,

essential for flight, insulate body• Wings- modified forelimbs, covered

by feathers• Lightweight, rigid skeleton- bones

are thin & hollow• Endothermic metabolism- high

body temperature

Characteristics• Unique respiratory system-

rapid metabolism, lungs connected to air sacs, oxygen-rich

• Beak- no teeth, horny sheath made of keratin

• Oviparity- lay amniotic eggs- eggs are incubated by both parents

Evolution• Similarities between birds &

dinosaurs• S-shaped neck, unique ankle joint,

& hollow bones• Thought to have evolved from

small, fast running dinosaurs• Archaeopteryx

Archaeopteryx

Archaeopteryx• Shapes of feathers are visible• Feathers cover wings, forelimbs, &

its body and tail

• Hollow bones & furcula- wishbone

• Teeth, claws on forelimbs, long tail

Origin of Flight• Hypothesis 1: ancestors of birds

were tree-dwellers that lived in trees- glided and wings evolved

• Hypothesis 2: ancestors of birds were land-dwellers- wings evolved to stabilize and protect against predators

Evolution after Archaeopteryx

• Only two of the modern orders of birds appeared after the mass extinction.

• 40 million years ago, most modern orders of birds originated

REVIEW!!!• List two unique features of a bird’s

skeleton.

• What are two functions of feathers?

• Identify the characteristics that birds have in common with dinosaurs.