Fossil record of Ceratophyllum aff. muricatum Cham. (Ceratophyllaceae) from the middle Eocene of central Tibetan Plateau, China

Abstract Ceratophyllaceae Gray is a cosmopolitan submersed family in angiosperm. The fossil record is mainly composed of fruits ranging in age from the Cretaceous to the Neogene within the Northern Hemisphere. However, its fossil record in Asia is sparse. Here we report on a fossil fruit attributed to Ceratophyllum aff. muricatum Cham. from the early middle Eocene of the Niubao Formation in Bangor County, central Tibetan Plateau, China, which is characterized by marginal lateral spines, a style and two basal spines and a small smooth, possibly warty body. This is the earliest fossil record of Ceratophyllaceae in Asia, and it indicates a dispersion from North America to Asia as well as a much wider distribution of Ceratophyllum during the Eocene than previously thought. Moreover, this fossil record demonstrates that the depositional site corresponds to a shallow freshwater environment. The climate was tropical to sub-tropical, consistent with environmental conditions of other fossils findings in the same site. Besides, the climate condition was totally different from the present, largely due to the Neogene formation of central Tibetan Plateau.