First record of Eretmophyllum (Ginkgoales) with well-preserved cuticle from the Middle Jurassic of the Ordos Basin, Inner Mongolia, China

Abstract

The genus Eretmophyllum, a characteristic and widespread taxon of the order Ginkgoales, is restricted in the Mesozoic floras of Eurasia. In China, although some specimens were assigned to Eretmophyllum based on gross leaf morphology, none have epidermal structure, which is essential for species delimitation within this genus. In this paper, we describe a new species, Eretmophyllum neimengguensis n. sp., from the Middle Jurassic Yan’an Formation of the Ordos Basin, China. This is the first record of the genus Eretmophyllum (Ginkgoales) from the Ordos Basin as well as from China based upon the gross leaf morphology and the epidermal structure. The new record significantly extends the stratigraphic and geographic distribution of Eretmophyllum in China and Eurasia. It also improves our understanding of its leaf morphology, epidermal structure, and past diversity. The taxonomic position and the stratigraphic and geographical range of the genus Eretmophyllum are discussed. Briefly, leaf morphological and epidermal characters of the new species, associated plant assemblages, and sedimentology indicate that the regional climate of the Ordos Basin was warm and humid with seasonal temperature and precipitation fluctuations in warm-temperate zone during the Middle Jurassic. Furthermore, given the relationship between the distribution/diversity of the genus and the climate, the genus Eretmophyllum may be confined to the warm-temperature climate, is intolerant of heat and frost, and can be considered as an indicator of humid and warm climatic conditions.