Diettertia montanensis, gen. et sp. nov., a fossil moss from the Lower Cretaceous Kootenai Formation of Montana

This is the first report of a moss gametophyte from the Cretaceous of western North America, and this moss may well be the oldest member of the Bryopsida recorded from the Mesozoic of North America. The fossils were collected from shales of the Lower Cretaceous Kootenai Formation of north central Montana. The general form of the fossil is dorsiventral, with a pinnately branched stem bearing small, remote, ovate, ecostate leaves that are inserted obliquely in an alternate, two-ranked arrangement on its upper surface. Lateral branches arise in association with leaves of the main axis and do not bear leaves for some distance from their point of origin. Cells of the stem are not differentiated into distinct layers or tissues. Isolated leaves appear slightly asymmetrical, possibly because of their oblique attachment. Leaf cells are elongate and thick-walled, with no evidence of differentiated alar cells. Apparently this moss occurred in considerable quantity at or near the area of deposition, since its remains are common in shale macerations.