site than from "era" to "era," in terms of the Chinese chronology, yet all form a whole that is distinct from that of the Han and other peoples of the non-Chinese north. In some instances, the iconography cannot be used as the main cultural identifier, because art depicting animal predation is common among the steppe peoples. An example of animal predation associated with Xiongnu culture is that of a tiger carrying dead prey. A similar motif appears in work from Maoqinggou, a site which is presumed to have been under Xiongnu political control but is still clearly non-Xiongnu. In the Maoqinggou example, the prey is replaced with an extension of the tiger's foot. The work also depicts a cruder level of execution; Maoqinggou work was executed in a rounder, less detailed style. In its broadest sense, Xiongnu iconography of animal predation includes examples such as the gold headdress from Aluchaideng and gold earrings with a turquoise and jade inlay discovered in Xigouban, Inner Mongolia. Xiongnu art is harder to distinguish from Saka or Scythian art. There is a similarity present in stylistic execution, but Xiongnu art and Saka art often differ in terms of iconography. Saka art does not appear to have included predation scenes, especially with dead prey, or same-animal combat. Additionally, Saka art included elements not common to Xiongnu iconography, such as winged, horned horses. The two cultures also used two different kinds of bird heads. Xiongnu depictions of birds tend to have a medium-sized eye and beak, and they are also depicted with ears, while Saka birds have a pronounced eye and beak, and no ears. Some scholars claim these differences are indicative of cultural differences. Scholar Sophia-Karin Psarras suggests that Xiongnu images of animal predation, specifically tiger-and-prey, are spiritual, representative of death and rebirth, and that same-animal combat is representative of the acquisition or maintenance of power. Rock art and writing The rock art of the Yin and Helan Mountains is dated from the 9th millennium BC to the 19th century AD. It consists mainly of engraved signs (petroglyphs) and only minimally of painted images. Chinese sources indicate that the Xiongnu did not have an ideographic form of writing like Chinese, but in the 2nd century BC, a renegade Chinese dignitary Yue "taught the Shanyu to write official letters to the Chinese court on a wooden tablet 31 cm long, and to use a seal and