Abstract: Two almost complete fossil hominid crania (EV9001 and EV9002) had been early reported to be found in 1989 and 1990 in Middle Pleistocene terrace deposit of Han River, Yunxian county, Hubei province, China. They are classified as Homo erectus. In this paper ten fossil animal teeth stratigraphically associated with the skulls were selected for electron spin resonance (ESR) dating. Since ESR ages depend on the behaviour of uranium in fossils, the closed system assumption was checked for the fossil samples and early uranium uptake model was applied to age determination. Single exponent function was used to fit the ESR intensity response to the irradiation dose and its appropriateness was discussed.
The mean age and the standard deviation for these samples are 581 ± 93 ka. It deviates from the geomagnetic dating result of 830-870 ka. The possible systematic errors in ESR dating were discussed and they could not account for the disagreement. Anyway the dating results place Yunxian crania in between the Homo erectus found at Lantian and Zhoukoudian and indicate that Yunxian crania constitute an important link in the human evolutionary lineage of China.

Key words: Homo erectus; Yunxian; Tooth enamel; ESR dating