Clam shrimp genus Ordosestheria from the Lower Cretaceous Dalazi Formation in Jilin Province, north-eastern China

Ordosestheria Wang, 1984 was originally described from the lower Aptian Jingchuan Formation (previously the sixth member of the Zhidan Group) in north-western China. It was recovered from the lower Barremian Bouhedma Formation in southern Tunisia. However, we identified species of Ordosestheria from the upper Albian Dalazi Formation in north-eastern China, which were previously identified as orthestheriids. This means that the distribution area of Ordosestheria is wider than we thought before. Through the SEM examination of specimens of Or. multicostata (Chen in Zhang et al., 1976), new features have been discerned: 1) small-sized polygonal reticulation occurs on growth bands near the umbo; 2) reticulation changes into evenly distributed puncta; 3) then widely spaced radial lirae with intercalated fine puncta; 4) puncta are disappeared on middle and lower part of the carapace, leaving an undulating upper part and a row of small pits along the lower margin of each growth band; 5) growth lines are serrated in their lower margins. As a result, Ordosestheria is also a principal component of the Yanjiestheria clam shrimp fauna, and can be an index genus for the subdivision of non-marine sequences in China.