The biggest, the smallest, the fastest, and the slowest are covered in Discovery Channel's tour of the animal kingdom. In Mammals we learn about our animal “classmates” and the fabulous variety they come in today. We also find out why they rule the earth. Reptiles have been walking, slithering or lumbering around the Earth for millions of years. Fish and Amphibians take a look at the most prominent creatures under water. Learn how fish and the amphibian's behaviour changes as they adapt to their environment. Take flight with Birds so you can take a closer look at our feathered friends. Did you know that you can guess what a bird eats by looking at its beak?