Discovery of Pseudofrenelopsis from the Lower Cretaceous of Liupanshan Basin and its paleoclimatic significance

The Lower Cretaceous strata are well developed and widely distributed in the Liupanshan Basin, Ningxia Hui Autonomous Region, NW China. A variety of spores and pollen have been discovered, whereas few megafossil plants have been reported. In the present study, a new cheirolepidiaceous species, Pseudofrenelopsis liupanshanensis, is described from the Lower Cretaceous Naijiahe Formation of the Liupanshan Basin based on the leaf morphological and cuticular features. The specimens are characterized by cylindrical leafy shoots with spirally and loosely arranged triangular leaves. The cuticles are strongly cutinized with very developed papillae and the absence of hairs or trichomes on the epidermis of the leaves and internodes. The stomata are longitudinally arranged in uniseriate files and irregularly oriented and commonly surrounded by 5–6 subsidiary cells. The present species is morphologically and micromorphologically distinct from other Pseudofrenelopsis species. A seasonal and arid or semi-arid climate is represented in the Liupanshan Basin during the late Early Cretaceous, which is indicated by fossil plant taxa and the leafy shoot morphological and epidermal structures of the present Pseudofrenelopsis. Furthermore, the dominant Classopollis, occurrence of gypsum layers and evidence of the carbon and oxygen isotopes also support these findings.