First record of Sphenarion (Czekanowskiales) with epidermal structures from the Middle Jurassic of Inner Mongolia, China

Abstract

The genus Sphenarion (Czekanowskiales) was first established for some fossil leaves from the Middle Jurassic Yorkshire flora of England. There are relatively few reports of Sphenarion with epidermal structures in the Mesozoic floras of Eurasia since its establishment. In this paper we describe a new species, Sphenarion angustae n. sp., from the Middle Jurassic Jiulongshan Formation near Daohugou Village, Inner Mongolia, China. This is the first record of the genus Sphenarion (Czekanowskiales) from the Daohugou Biota and from China based upon the gross leaf morphology and the epidermal structures. The new species has 7–8 persistent, linear leaves clustered on a short shoot. The amphistomatic leaves, with distinctive stomatal and nonstomatal zones on both upper and lower epidermis are simple or mostly fork once. The new species provides new morphological and epidermal data and extends stratigraphic and geographic distribution of Sphenarion in Eurasia. Meanwhile, the new discovery is significant in understanding the floral composition, paleoclimate, and paleoenviroment of the Daohugou Biota. Analysis of the cuticular structures presented here and preliminary examination of other associated plant groups suggest that the new species grew in an area with a seasonal warm and humid climate in a warm-temperate zone.