Characteristics of Animals

Characteristics of All Fish

1. They are ectothermic, aquatic vertebrates.
2. Their skin is generally covered with scales.
3. Their limbs are modified into fins for swimming.

Characteristics of All Amphibians

1. They are ectothermic vertebrates.
2. Their skin is usually smooth and lacks scales, hair, and feathers. They are dependent upon moisture and subject to desiccation; their skin must remain moist to aid in breathing.
3. They have three-chambered hearts.
4. They lack claws on their toes.

Characteristics of All Reptiles

1. They are ectothermic vertebrates.
2. Their skin has scales, but no hair or feathers.
3. They have three-chambered hearts (except for alligators and crocodiles, which have four-chambered hearts).
4. They have claws on their toes (except those which do not have legs, such as legless lizards).
5. They are the first animals, in evolution, to develop the amniotic egg.  This allows reptiles to lay eggs on land.

Characteristics of All Birds

1. They are endothermic vertebrates.
2. Their skin is covered with feathers.
3. They have four-chambered hearts.
4. Their bones are lightweight and usually hollow.
5. Their forelimbs are modified as wings.
6. They lay eggs.

Characteristics of All Mammals

1. They are endothermic vertebrates.
2. They have hair, which varies greatly among species.
3. Most have sudoriferus (sweat) glands.
4. They have mammary (milk-secreting) glands.
5. They have sebaceous (fat-secreting) glands.
6. They have heterodont dentition (different types of teeth).