Earth is the only planet known to date that supports life. A few million years ago, Earth was home to one of the most vicious and devastating creatures known to mankind: dinosaurs. Enveloped in a cocoon of evolution, the Earth, like most living things, has undergone a metamorphosis, transforming the world as it is today. Gigantic, deadly dinosaurs went extinct, while only a minority that survived mutated into smaller animals. The animals that roam the Earth are classified into three broad categories, namely mammals, reptiles and amphibians, where each category is divided into respective orders (see Figure 1 in Appendix 1). The first major type of animal is the mammal. There are over 4,000 different species of mammals. The smallest is the hog-nosed bat, which weighs 0.05 ounces. The largest is the blue whale, which can be 100 feet long and weigh 150 tons. But whether they live on land or in water, all mammals share certain common characteristics. All mammals are vertebrates. They either have a backbone or a backbone. Furthermore, all mammals are endothermic, also called “warm-blooded”. They regulate their own body temperature, allowing them to live in almost any climate on Earth. Mammals have hair or fur on their bodies. In addition, they produce milk to feed their babies. This allows them to spend more time with their young and teach them important skills they need to survive on their own. As Peterson (2006) mentioned, the word mammal is derived from the milk-producing mammary glands that are unique to the class Mammalia. Mammals owe their spectacular success to many characteristics. Many of the most important and diagnostic features of mammals serve to enhance intelligence and sensory abilities, (middle of article......alliday, 2002). The caecilian is a type of Gymnophionan. Works Cited Vaughan, T. A. (1986). Mammalogy. New York, NY: Saunders College Publishing. Eisenberg, J.F. (1999). Mammals of the neotropics (volume 3): the central neotropics: Ecuador, Peru, Bolivia, Brazil. New York, NY: University Of Chicago Press. O’Shea, M. and Halliday, T. (2001). Reptiles and amphibians. New York, NY: DKPublishing. Ballinger, R.E. and Lynch, J.D. (1983). How to know about amphibians and reptiles. New York, NY: Wm. C. Brown Company Publishers Dubuque, Iowa. Tyning, T. F. (1990). A Guide to Amphibians and Reptiles. New York, NY: LB, Little, Brown and CompanyCook, FR (2007). Amphibians. Retrieved from www.thecanadianencyclopedia.ca/en/article/amphibian Peterson, RL (2006). Mammal. Retrieved from http://www.thecanadianencyclopedia.ca/en/article/mammal/