The discovery of clam shrimp (Spinicaudata) from the Hekou Group of Lanzhou, Northwest China: Implications for Taxonomy and Biostratigraphy.

The geological age of the Hekou Group in the Lanzhou-Minhe Basin of northwestern China has long been controversial, with most opinions suggesting that it is of an Early Cretaceous age. Our first recovery of a Yanjiestheria clam shrimp fauna in the upper part of the Lower Subgroup of the Hekou Group in the standard section in Lanzhou also supports an Early Cretaceous age for the fossil-bearing beds. Through the scanning electron microscope (SEM) examination of specimens of Yanjiestheria haishiwanensis Wang in Shen et al., 1982, fine reticulations on the antero–ventral and middle parts of the carapace have been clearly observed, which were overlooked in the original description due to the poor preservation. Nemestheria was also found for the first time in the Hekou Group. • First discovery of clam shrinp in the type section of Hekou Group in Lanzhou. • The Yanjieshteria fauna indicates an Early Cretaceous age for the fossil beds. • First recovery of Nemestheria in the Hekou Group. [ABSTRACT FROM AUTHOR]