Imagine a fish with legs! Once upon a time, there really was an animal that looked like a fish with legs. Most scientists believe that about 400 million years ago it swam in the warm, green waters...
Fish in armor
According to most scientists, the fishes that swam in the seas 430 million years ago were covered with hard, bony armor. They had no jaws like the fish of today. Their mouths were just holes in the...
Strange sea animals
Scientists say that five hundred million years ago all plants and animals lived in the sea. There were sponges, jellyfish, worms with legs, and things like clams. And there was another animal that...
Animals of Long Ago
Imagine animals like fish with legs. Imagine trees like giant feather dusters. That's what some animals and trees looked like, once. Just as you change as you grow older, the world changes and the...
Change or die!
Eohippus Scientists think the eohippus was the ancestor of the modern horse. The eohippus was a small animal that had toes instead of hoofs. Suppose that all the milkweed plants in the world...
Natural enemies
Most animals have natural enemies---other animals that like to eat them. It's night on a desert in the United States. A wolf spider is hunting. The spider is the natural enemy of beetles and other...
Keeping things even
Once, several thousand deer and a few dozen mountain lions lived together in a part of Arizona. Each year, the mountain lions ate hundreds of deer. But, during the year, hundreds of new deer were...
Keep out!
Some animals hunt for food in many different places and sleep wherever they happen to be. But other animals always sleep and hunt in the same place. This place is their territory. A dragonfly's...
Life in low places and high places
Underground caves are blacker than a lump of coal. Mountaintops are cold and bare. It doesn't seem possible for animals to live in these places. But animals do live in them. Small, white fish swim...
Nature’s clean-up crew
What becomes of the leaves that fall in the forest every autumn? What keeps them from piling up each year and covering the world with leaves? Each spring, millions of baby insects eat into the...
