Sprecher
Beschreibung
A permineralized ovulate cone of Metasequoia Miki (Cupressaceae), representing the oldest record of the genus in Japan, was discovered in the Upper Cretaceous Obisagawa Member of the Ashizawa Formation, Futaba Group (latest Turonian to earliest Coniacian), in Hirono Town, Fukushima, Japan. Here we report its anatomical features and affinities, focusing on the evolutionary history of Metasequoia. The specimen is preserved in a calcareous concretion with numerous plant fragments, including isolated seeds, leaves, and shoots of various affinities. Gross morphology was preliminarily assessed using microfocus X-ray CT, and internal anatomy was studied using serial peel sections, with 3D rendered images. The ovulate cone is nearly cylindrical, ca. 33 mm long and 28 mm wide, and terminates on a sparsely leaved stalk. Fourteen cone scale complexes, arranged decussately on the main axis, bear at least seven ovules, with their micropyles oriented toward the main axis. Along with these cone features, the associated shoots with opposite leaves and the circular winged seeds support its assignment to Metasequoia. Three fossil species are currently accepted in the genus: M. milleri, M. foxii, and M. occidentalis. The new specimen is anatomically distinct from all known species in the genus. Notably, the specimen possesses a uniseriate ring of resin canals internal to the central vascular bundle ring of the cone scale complex. Furthermore, the vascular bundle course within the complex may exhibit characteristics intermediate between Metasequoia and Sequoia. This study provides important insights into the early evolutionary history and morphological diversity of Metasequoia during the Late Cretaceous.