Suturovagina intermedia (Cheirolepidiaceae) from the Lower Cretaceous Dalazi Formation of Wangqing, Northeast China: Cuticle ultrastructure and palaeoenvironmental insights

The Cheirolepidiaceous conifer Suturovagina intermedia Chow et Tsao is reported from the Lower Cretaceous of Wangqing, Jilin Province in northeastern China, and its leaf cuticles were studied in detail using scanning and transmission electron microscopies and EDS. The data obtained were compared with those of the previous study on the same species from the Lower Cretaceous of the type locality Nanjing, Jiangsu Province in eastern China. Despite the general similarity in gross morphology and leaf cuticular structure, there are a number of differences in leaf cuticular ultrastructure and element composition (EDS data) between specimens from the two localities. Among them, 14 differences are potential taxonomical characters. Of them, 7 might be of importance at the species/genus level, and 7 are possible characters at the family level. There are also 23 differences, i.e., 7 cuticle ultrastructural characters of ordinary epidermal cell cuticles and 5 subsidiary cell cuticles, plus 11 EDS ratios of cuticles, believed to be of ecological significances. This paper presents the first case to make comparative palaeoenvironmental analyses based on leaf cuticle ultrastructure and element composition of the same taxon from different areas. It shows that Suturovagina intermedia was an inhabitant of a lower xerothermic environment in Wangqing, instead of being a higher xerothermic environment, such as in the type locality Nanjing. The conclusion obtained is well-supported by the evidence of the element composition (EDX data) of the matrix and the associated biotic composition of the fossil-bearing beds from the two localities. It is the first attempt to search for the environmental footprint in fossil plant cuticles based on their element composition.