The age of the dinosaur-bearing Cretaceous sediments at Dashuiguo, Inner Mongolia, P.R. China based on charophytes, ostracods and palynomorphs

The Dashuiguo Formation has yielded numerous fossils of Probactrosaurus, a dinosaur with both iguanodontid and hadrosaurid characteristics. Based on the evolutionary position of Probactrosaurus, the dinosaur-bearing sediments have been considered to be Aptian–Albian, but new micropalaeontological data (charophytes, ostracods and palynomorphs) indicate that they may be as old as Barremian. The three charophyte species recovered are indicative of a Barremian–Aptian age. A rich fauna of non-marine Ostracoda (13 species in nine genera) includes two species described as new, Cypridea pseudomodica sp. nov. and C. dashuiguoensis sp. nov., while the remaining eleven species have been described previously from Lower Cretaceous sediments of the Gobi Basin and adjacent areas in China. Based on the ostracod assemblage, the Dashuiguo Formation can be correlated with the Dzun Bayn suite of the Gobi Basin and can therefore be regarded as Barremian–Albian in age. The palynomorph assemblage is very similar to that described from the nearby Tebch site with an estimated Barremian–Early Aptian age and is radiometrically calibrated on the basis of an overlying basalt layer.