At this point in the earth's history, the earliest four-legged animals were coming out of the water onto land.

Based on the results from earlier animal and human studies regarding intrinsic motivation the author explored two possibilities.

The earlier animals, hot and weary with their grovelling, shot vicious glances at him.

They are also probably the earliest animals in which two sexes can be certainly identified.

This may have played an important role in the development of the earliest animals.

Most human genes have an ancestry that goes back to the earliest animals and are shared in common with other species.

Invertebrates were the earliest animals, appearing on earth between three and five billion years ago.

The trilobites were among the most successful of all early animals, roaming the oceans for over 270 million years.

Obviously there are distances that could not have been jumped by the earliest animals with proto-wings.

The dog, along with the pig, were the earliest animals domesticated in China.