The Chinese zodiac is based on twelve different signs. Sacred animals combined with five elements are resulting in sixty typologies of personality, philosophy of life and destiny. Chinese astronomers assigned five mainplanetsto five elements, so that Mercury equals water, Venus equals metal, Mars equals fire, Jupiter equals wood, and Saturn equals earth. Those elements, as well as the position of planets, the moon, the sun or comets, determine the character of a person in time of birth. Also in the Chinese zodiac the date of birth defines the sign of the zodiac. However, they are not divided into months as in the westernSigns of the Zodiac, but into years.
There are different narratives explaining why the twelve animals define the signs. The most common one is a Chinese legend: Buddha sent to call all animals on earth, however only a few appeared. The rat was the first animal to arrive, that's why it's marking the first year. Then the buffalo turned up and as the animals were appearing, they were assigned to the zodiac.