Taxodiaceous pollen cones from the Upper Cretaceous (Horseshoe Canyon Formation) of Drumheller, Alberta, Canada

Abstract

One hundred permineralized cones, 1.0–1.2 mm × 1.5-2.0 mm, some attached to branching systems, have been examined from the Upper Cretaceous ironstones in the Horseshoe Canyon Formation near Drumheller, Alberta. Cones are borne laterally and terminally on specialized shoots. Microsporophylls are helically arranged on the cone axis with one large resin canal and two pollen sacs per microsporophyll. Pollen is 12–16 μm in diameter with one exit papilla that forms a low protuberance on the grain. External surfaces of grains are scabrate with numerous orbicules and macrogranules while the nexine is laminated. Arrangement of cones on branches is similar to those of Taxodium whereas the number of pollen sacs per microsporophyll is similar to Sequoia and Sequoiadendron. Pollen morphology is similar to Metasequoia and Taxodium, while ultrastructurally it most closely resembles that of Metasequoia. This combination of morphological features is unlike that found in any living taxodiaceous genus. These remains are therefore described as Drumhellera kurmanniae gen. et sp. nov. This study reveals the importance of whole plant reconstructions of other fossil Taxodiaceae due to the scarcity of distinctive morphological characters in isolated organs. Furthermore, the large number of fossil plant specimens associated with these taxodiaceous remains in the Horseshoe Canyon Formation show enormous potential for reconstructions of several types of seed plants.