Cuticular anatomy of Comia(Pteridospermae) from the Upper Permian of Yumen in Gansu Province, Northwestern China, and palaeoatmospheric CO_2 reconstruction

Comia macrofossils have been widely known from rocks of the Late Permian age in the Angaran and Cathaysian Palaeobiogeographic regions. However, the epidermal structure of the genus has not been reported. The new material with wellpreserved cuticles obtained from the Late Permian Sunan Formation in the west of Gansu Province, Northwestern China allows a new species to be attributed to this genus, namely Comia dashankouensis Dong C et Sun BN sp. nov. The cuticular features of the genus are described, including the general structures of lower and upper cuticles, stomata, and papillae. The stomatal density(SD) and stomatal index(SI) of fossil cuticles are routinely used today as a proxy in the reconstruction of palaeoatmospheric CO2 levels for the Cenezoic, Mesozoic, and Paleozoic eras. In particular, the cuticles of cycads, ginkgoes, conifers, and pteridosperms have frequently been used for this purpose. Within this study, the CO2 concentration of the early Late Permian was reconstructed by performing stomatal frequency analysis of these Comia fossils, suggesting a maximum palaeoatmospheric CO2 concentration of 1929.5 ppmv, consistent with the estimates obtained using GEOCARB III, and a minimum of 1157.8 ppmv, consistent with the estimates obtained using GEOCARB II.