Mammal fossil is a collective term for fossils of the phylum Mammalia. Mammals have a wide range of sizes from as small as a mouse to as large as an elephant. They are warm-blooded and viviparous animals. The identification of the species, genus and even upper classifications of mammals relies on the tooth forms and array characteristics. The evolutionary sequence of mammals’ molar morphology is from small to large, simple to complex crowns, and low to tall crown heights. Herbivores such as deer, sheep, rhinoceros and horse have crescent-shaped tooth crowns. Carnivores such as tigers and dogs have a pair of canine teeth, and their molars are conical (like a penholder). Omnivores such as pigs, giant pandas, apes and ape men have degenerated canine teeth and hill-shaped molars.