The oracle bones are mostly tortoise plastrons (ventral or belly shells, probably female) and ox scapulae (shoulder blades), although some are the carapace (dorsal or back shells) of tortoises, and a few are ox rib bones, scapulae of sheep, boars, horses and deer, and some other animal bones.
The skulls of deer, oxen and humans have also been found with inscriptions on them, although these are very rare and appear to have been inscribed for record keeping or practice rather than for actual divination; in one case, inscribed deer antlers were reported, but Keightley (1978) reports that they are fake.
Neolithic diviners in China had long been heating the bones of deer, sheep, pigs and cattle for similar purposes; evidence for this in Liaoning has been found dating to the late fourth millennium BCE.
However, over time, the use of ox bones increased, and use of tortoise shells does not appear until early Shang culture.
The earliest tortoise shells found that had been prepared for divinatory use (i.e., with chiseled pits) date to the earliest Shang stratum at Erligang (Zhengzhou, Henan).
By the end of the Erligang, the plastrons were numerous, and at Anyang, scapulae and plastrons were used in roughly equal numbers.
Due to the use of these shells in addition to bones, early references to the oracle bone script often used the term "shell and bone script", but since tortoise shells are actually a bony material, the more concise term "oracle bones" is applied to them as well.

The bones or shells were first sourced and then prepared for use.
Their sourcing is significant because some of them (especially many of the shells) are believed to have been presented as tribute to the Shang, which is valuable information about diplomatic relations of the time.
We know this because notations were often made on them recording their provenance (e.g., tribute of how many shells from where and on what date).
For example, one notation records that "Què (雀) sent 250 (tortoise shells)", identifying this as, perhaps, a statelet within the Shang sphere of influence.
These notations were generally made on the back of the shell's bridge (called bridge notations), the lower carapace, or the xiphiplastron (tail edge).
Some shells may have been from locally raised tortoises, however.
Scapula notations were near the socket or a lower edge.
Some of these notations were not carved after being written with a brush, proving (along with other evidence) the use of the writing brush in Shang times.
Scapulae are assumed to have generally come from the Shang's own livestock, perhaps those used in ritual sacrifice, although there are records of cattle sent as tribute as well, including some recorded via marginal notations.
The oracle bones are mostly tortoise plastrons (ventral or belly shells, probably female) and ox scapulae (shoulder blades), although some are the carapace (dorsal or back shells) of tortoises, and a few are ox rib bones, scapulae of sheep, boars, horses and deer, and some other animal bones. The skulls of deer, oxen and humans have also been found with inscriptions on them, although these are very rare and appear to have been inscribed for record keeping or practice rather than for actual divination; in one case, inscribed deer antlers were reported, but Keightley (1978) reports that they are fake. Neolithic diviners in China had long been heating the bones of deer, sheep, pigs and cattle for similar purposes; evidence for this in Liaoning has been found dating to the late fourth millennium BCE. However, over time, the use of ox bones increased, and use of tortoise shells does not appear until early Shang culture. The earliest tortoise shells found that had been prepared for divinatory use (i.e., with chiseled pits) date to the earliest Shang stratum at Erligang (Zhengzhou, Henan). By the end of the Erligang, the plastrons were numerous, and at Anyang, scapulae and plastrons were used in roughly equal numbers. Due to the use of these shells in addition to bones, early references to the oracle bone script often used the term "shell and bone script", but since tortoise shells are actually a bony material, the more concise term "oracle bones" is applied to them as well.
The bones or shells were first sourced and then prepared for use. Their sourcing is significant because some of them (especially many of the shells) are believed to have been presented as tribute to the Shang, which is valuable information about diplomatic relations of the time. We know this because notations were often made on them recording their provenance (e.g., tribute of how many shells from where and on what date). For example, one notation records that "Què (雀) sent 250 (tortoise shells)", identifying this as, perhaps, a statelet within the Shang sphere of influence. These notations were generally made on the back of the shell's bridge (called bridge notations), the lower carapace, or the xiphiplastron (tail edge). Some shells may have been from locally raised tortoises, however. Scapula notations were near the socket or a lower edge. Some of these notations were not carved after being written with a brush, proving (along with other evidence) the use of the writing brush in Shang times. Scapulae are assumed to have generally come from the Shang's own livestock, perhaps those used in ritual sacrifice, although there are records of cattle sent as tribute as well, including some recorded via marginal notations.
Oracle bone