Uranus is the only planet that rotates on its side.
The only river that flows both north and south of the equator is the Congo. It crosses the equator twice.
The Joshua tree is the only tree that grows in California's Mojave Desert.
The only rock that floats in water is pumice.
The penguin is the only bird that can swim, but not fly. It is also the only bird that walks upright.
The only lizard that has a voice is the Gecko.
The hummingbird is the only bird that can fly backwards.
Giraffes are the only animals born with horns. Both males and females are born with bony knobs on the forehead.
Bats have only one baby a year.
Bats are the only mammal that can fly.
