Structurally preserved Nilssoniopteris from the Arida Formation (Barremian, Lower Cretaceous) of southwest Japan

Strap-shaped foliage previously assigned to Nilssonia ex. gr. schaumburgensis is redescribed as Nilssoniopteris oishii sp. nov., based on structurally preserved foliage from the Barremian Arida Formation in Yuasa District, Wakayama Prefecture, southwest Japan. The newly assigned bennettitalean affinity of the fossil was confirmed with its cuticular morphology exhibiting paracytic (syndetocheilic) stomata, and rachis anatomy. Rachis vascular bundles are basically arranged in a circular form, which is dissected at both lateral sides for the pinna trace departure. This vascular configuration is similar to those of other bennettitalean genera and different from inverted-omega-shaped or C-shaped vascular configuration in the Cycadales. N. oishii is most abundantly found in the Ryoseki-type fossil assemblages which flourished under the dry conditions. This study clears the discrepancy between the abundance of “Nilssonia ex. gr. schaumburgensis” under dry climates and the general climatic preference of Nilssonia species to humid conditions.