First record of charcoalified sphenopterid mesofossils from the Serpukhovian (Mississippian, early Carboniferous) Jingyuan (Tsingyuan) Formation in Gansu Province, western China

Anatomical characteristics of three charred mesofossils are described from the Serpkhovian Jingyuan (Tsingyuan) Formation (Mississippian, early Carboniferous) in the Ciyao Section, Baiyin City, Gansu Province, western China. They are attributed to three types based on morphology, corresponding to the well-known, late Palaeozoic (uppermost Devonian-Permian) sphenopterid foliage. All of these three morphologic types of mesofossils have similar epidermal characteristics: the differentiation of costal and intercostal fields in both upper and lower epidermis, the same shape of the epidermal cells, similar simple stomata with only two bean-shaped guard cells but without subsidiary cells, the same distribution and orientation of stomata in the upper epidermis, and trichome bases in the costal fields of the lower epidermis. It is inferred that, based on the similarity of the anatomical characteristics, these three types of mesofossils could be derived from the same species of parent plant, although it appears that there are some differences in morphology. The presence of trichome bases in the costal fields of upper epidermis of the fossils is most probably an ecological adaptation to insect activity as observed in extant plants. Our record of charcoalified mesofossils for the first time demonstrates the occurrence of Mississippian wildfire in the North China Block, then located in eastern Pangaea, appearing as a tropical island in Palaeotethys Ocean.