Reptiles, Birds, and Mammals are Amniotes

Have a membranous sac called the amnion that surrounds &

protects the embryo

Three characteristics of amniotes decrease their dependency on water

1. Amniotic egg – waterproof egg with a covering – inside the egg is a fluid-filled cavity in which the embryo develops

2. Internal fertilization – male deposits sperm within the reproductive system

3. Water-tight skin – made out of a protein called keratin; prevents dehydration & acts as a barrier

May be hair, nails, scales, or feathers

Endotherm Ectotherm-”regulator” -”conformer”-temperature stays constant -temperature changes with -birds, mammals external environment

-reptiles, amphibians, fish

Reptiles (Class Reptilia)Turtles, lizards, snakes, crocodiles, alligators

Water-tight skin is made out of scales – hard, overlapping layers of protein

Scales cannot expand, so to grow bigger a reptile must molt

Most lay eggs, but some give birth to live young

Birds (Class Aves) are endothermic amniotes

with specialized adaptations for flight

Evolved from small dinosaurs

Because birds are endotherms, they lay eggs that must be kept warm by brooding

Song Sparrow brood patch

Special adaptations for flight:

1. Wing shape – produces lift for flight

2. Feathers – modified scales – function in flight, waterproofing, and endothermy

3. Air sacs – function with lungs in respiration – needed to meet intense oxygen demands for flight – reduces body density (makes it lighter for flight)

4. Honeycombed bones makes lighter

Bird bone(much lighter)

Human bone

5. No teeth to reduce weight of head-instead they have a gizzard, a muscular organ that

grinds food

Structure fits Function – Beak Shape

Arguably the Most Exquisitely EvolvedMating Behaviors Belong to Class Aves