bird

An endothermic vertebrate that lays eggs and has feathers and a four-chambered heart.

contour feather

A large feather that helps give shape to a bird's body.

down feather

A short, fluffy feather that traps heat and keeps a bird warm.

crop

An internal organ of many birds that stores food inside its body after swallowing it.

gizzard

A muscular, thick-walled part of a bird's stomach that squeezes and grinds partially digested food.

lift

The difference in pressure between the upper and lower surfaces of a bird's wings that produces an upward force that causes the bird to rise.

mammal

An endothermic vertebrate with a four-chambered heart and skin covered with fur or hair, that feeds its young with milk from the mother's body.

diaphragm

A large muscle located at the bottom of a mammal's rib cage that functions in breathing.

monotreme

A mammal that lays eggs.

marsupial

A mammal whose young are born at an early stage of development, and which usually continue to develop in a pouch on their mother's body.

gestation period

The length of time between fertilization and birth of a mammal.

placental mammal

A mammal that develops inside its mother's body until its body systems can function independently.

placenta

A membrane that becomes the link between the developing embryo or fetus and the mother

mammary gland

An organ in female mammals that produces milk for the mammal's young.

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