In which dynasty did the zodiac start?

It is difficult to study the origin of the zodiac. For a long time, many people regard Lun Heng as the earliest document that records the zodiac. Lun Heng is the representative work of Wang Chong, a materialist thinker in the Eastern Han Dynasty. "On the Balance of Things" contains: "Yin, wood, birds and tigers. Soil, its birds and dogs are also. ..... At noon, the horse also arrived. Son, mouse knife. Unitary, chicken also. Hair, rabbits, too. ..... hey, tapir. No, so are sheep. Ugly, cattle also. ..... Third, snakes are also. Shen, Qitian also. " There are only eleven zodiac signs in the above quotation, but the dragon is missing. The book "Poisonous Words" also said: "Chen Weilong, Si is a snake, and Chen and Si are in the southeast. In this way, the zodiac is complete, and the subordinate relationship between the twelve earthly branches and the zodiac is also so complete, just like today.