Kimuriella gen. nov. (Bennettitales), a Whole-Plant Bennettite from the Oxfordian (Upper Jurassic) Tochikubo Formation of Shidazawa, Minamisōma, Fukushima Prefecture, Northeast Japan

Abstract

A new whole-plant bennettite—Kimuriella densifolia—is described and restored based on excellently preserved fossils from the Oxfordian (Upper Jurassic) Tochikubo Formation of Northeast Japan. Recent excavations revealed plant fossils with axes, sterile foliage and ovuliferous Williamsonia type flowers in organic connection. The sterile foliage of the plant is identical to what is described as Zamites nipponicus when found isolated. Microsporangiate flowers of the Weltrichia type were preserved together with the articulated macrofossils and conspecificity is strongly warranted. The absence of an appropriate plant genus to accommodate the restored plant based on the articulated fossils necessitated the erection of the new genus Kimuriella for whole-plant bennettites with a divaricate growth habit and Zamites type foliage. Kimuriella densifolia is compared with a number of coeval bennettites, amongst which the very similar Williamsonia gigas and Williamsonia pecten from the Bajocian of Yorkshire, UK. Nomenclatural issues of the latter two bennettite species are discussed in detail when research on the different organs assigned to them raised some questions connected with the classical circumscription of the taxa complying with the concept of form-classification of fossil plant organs. Finally, some interpretations of the coastal/river delta environment and habitat, in which Kimuriella densifolia thrived, are discussed.