Lauraceous Fossil Flowers from the Kamikitaba Assemblage (Coniacian, Late Cretaceous) of Northeastern Japan (Lauraceae)

Abstract

A new genus and species of Lauraceae, Microlaurus perigynus gen. et sp. nov. is described based on fossil charcoalified flower buds recovered from the Kamikitaba assemblage (early Coniacian, Late Cretaceous; ca. 89 million years before present (myr BP)) in the Ashizawa Formation (Asamigawa Member) of the Futaba Group in northeastern Japan. Analysis of the internal structure of the fossil buds using synchrotron-radiation X-ray microtomography (SRXTM) at the 2-BM-B beamline of the Advanced Photon Source (APS), Argonne National Laboratory, shows that the flowers are small, pedicellate, bisexual, trimerous, and actinomorphic, with small outer tepals, larger inner tepals, three whorls of stamens, an innermost androecial whorl composed of staminodia, and a unicarpellate gynoecium containing a single ovule. Microlaurus perigynus is assigned to the Lauraceae based on the regular trimerous floral organization and other details of floral structure, but it is distinguished from most previously described lauraceous fossil flowers by the poorly differentiated filament and anther in the stamens of the third whorl and the marked size difference between the small outer tepals and the large inner tepals. Also unusual are the paired glandular appendages that appear to be associated with the first (outermost) whorl of stamens, rather than the stamens of the third whorl, although the precise position is not fully clear. The same feature occurs in Hernandiaceae, the sister group of Lauraceae, as well as in Powhatania connata, an earlier but fragmentary lauralean fossil flower from the Early to Middle Albian of Virginia. Microlaurus perigynus adds to the floral diversity of Lauraceae known from the Late Cretaceous, and its presence in the Kamikitaba assemblage from Japan underlines the broad geographic distribution and floristic significance of lauraceous plants during the Late Cretaceous.