Oracle bones were popular tools for divination in ancient China, during that period of the Shang Dynasty, 1776-1122
B.C.E. Two primary objects were utilized, the bones of a now-extinct species of tortoise (Pseudocardia anyangensis ) and the shoulder bones of oxen. The tortoise was a sacred animal in China and appears as a symbol in various divinatory systems including astrology. It was symbolic of long life and was considered a guardian of graves. The ox also acquired an array of symbolic meanings.
Pseudocardia anyangensis was bred in ancient China. The part utilized for divination was the relatively soft and flat underlayer called the plastron. It was cleaned, and a number of cavities were cut into the surface. Questions would then be put to the plastron. To discover an answer, a heated rod would be pressed on one of the cavities and in a short time, a crack would appear on the reverse side of the surface. The crack would then be analyzed for its suggested portents. The majority of the surviving examples appear to have been used on behalf of the ruler by court diviners. Many exist only as fragments, as the process of divination often caused the plastron to break in two. In the case of shoulder bones, one end of which is flat, a similar process to that used on the tortoise plastrons was used. Half of the socket would be removed along with the longitudinal ridge, leaving a flat piece of bone with a handle. The first burns would be made on the end of the blade away from the handle. It also appears that the questions put to the bones would have been asked multiple times in order to determine the drift of the answers rather than simply relying on one response.
Archeologists have uncovered extensive collections of oracle bones of both varieties, in many cases bearing a number indicating the use of a filing system. At some point, however, after the fall of the Shang Dynasty, the use of oracle bones gave way to other popular systems of divination, especially the I Ching.
Temple, Robert K. G. Conversations with Eternity: Ancient Man's Attempt to Know the Future. London: Rider, 1984.