Cratostracus? cheni, a new conchostracan species from the Yixian Formation in western Liaoning, north-east China, and its age implications

The conchostracan genus Cratostracus was described from the Cenomanian Qingshankou Formation that crops out in the Jilin and Heilongjiang provinces of China, and species attributable to it have been found to range down into the Guantou Formation in Zhejiang Province, which has been dated as Aptian. Representatives of the genus have not been found previously in older rocks. The species described in this paper as Cratostracus? cheni sp. nov. was recovered from two sections of the Yixian Formation in western Liaoning Province. Although only tentatively attributed to Cratostracus, its occurrence is consistent with an Early Cretaceous rather than a Late Jurassic age for the formation.