Fossil seed cones of Fokienia (Cupressaceae) from the Paleocene Ravenscrag Formation of Saskatchewan, Canada

Abstract

Foliage bearing seed cones that are remarkably similar to those of extant Fokienia (Cupressaceae) have been recovered from early Paleocene sediments of the Ravenscrag Formation, southwestern Saskatchewan, Canada. The cones are borne in opposite pairs, are about 12.0 mm long and 10.0 mm wide, with 8–10 woody, decussate, peltate scales. Foliage branches oppositely and bears thin, flattened leaves in whorls of four. Although branching pattern and leaf morphology differ from that of modern Fokienia, similarity in seed cone structure allows assignment to this genus. These fossil remains indicate that cone structure comparable to modern Fokienia had evolved by the earliest Tertiary and has probably remained stable since. The vegetative remains indicate, however, that leaf and branch morphology has continued to evolve over this period of time (mosaic evolution), or that the diversity of morphological forms has in the past been greater in Fokienia and that extinction has limited this diversity. Such data reinforce the principle that seed cone structure should be the basis for identification of fossil Cupressaceae remains. Key words: Fokienia, Cupressaceae, Paleocene, fossil, seed cones, evolution.