Fig. 45 in The cephalopods of the Boda Limestone, Late Ordovician, of Dalarna, Sweden

Fig. 45. Hypothesis about the phylogenetic relationship of selected Ascocerida and Barrandeocerida. Note the phylogenetic trend of decoiling in ascocerids. The diversification of ascocerids occurred during the late Mid Ordovician. Star = truncation; 1 = thin subcentral siphuncle with orthocerid-like thin connecting ring; 2 = uncoiling. The close phylogenetic relationship between the uranoceratid Warburgoceras gen. nov. and ascocerids is based on the general similarity of shell shape, ornamentation, sipho-position and connecting ring shape of Redpathoceras Flower, 1963. Note also that Montyoceras titaniforme Flower, 1941 is larger, more rapidly expanding and more strongly coiled than the type of the genus, and thus much more similar to Redpathoceras. Figures of Hebetoceras Flower, 1941; Montycoceras Flower, 1941; Probillingsites Flower, 1941; Billingsites Hyatt, 1884; Schuchertoceras Miller, 1932; and Ascoceras Barrande, 1847 are modified from Kesling (1961). Figures of Choanoceras Lindström, 1890 are based on Furnish & Glenister (1964a); those of Deckeroceras Foerste, 1935 and Barrandeoceras Flower, 1950 are based on Sweet (1964a).