Solenoceras Conrad, 1860

KENNEDY, W. J., LANDMAN, N. H., COBBAN, W. A. & SCOTT, G. R., 2000, Late Campanian (Cretaceous) Heteromorph Ammonites From The Western Interior Of The United States, Bulletin of the American Museum of Natural History 2000 (251), pp. 1-88 : 72-73

Genus Solenoceras Conrad, 1860

TYPE SPECIES: Hamites annulifer Morton, 1841: 109, 1842 , p. 213, pl. 11, fig. 4 by the subsequent designation of Conrad, 1860: 284.

DIAGNOSIS: A small genus that consists of two straight shafts in tight contact with the

older shaft extending, straight or slightly curved, beyond the aperture and arising from a minute ammonitella coil (fig. 66). With the exception of a very small tear-shaped opening at the elbow, the younger shaft has a prominent impressed dorsal furrow resulting from growth of that shaft over the dorsum of the older shaft. Constrictions may or may not be present on both shafts, but the aperture is usually preceded by a conspicuous constriction bounded by high ribs (figs. 58, 66). Ornament consists of narrow, straight, closely spaced ribs that are prorsiradiate on the older shaft and rursiradiate on the younger shaft. Each rib ordinarily bears a minute tubercle on each side of the venter. Size dimorphism is present.

DISCUSSION: Morton’s type specimen, well illustrated by Reeside (1962, pl. 70, figs. 8– 10), is a small densely ribbed body chamber 21 mm long that begins at the elbow. Conspicuous constrictions are present in the middle of the elbow, in the middle of the shaft, and at the aperture; at the aperture the constriction is bounded by high ribs. Tubercles bordering the venter are barely visible.

The early growth stages of Solenoceras have not been previously described or illustrated. The restoration shown in figure 66 is based mainly on juvenile growth stages of specimens found in calcareous concretions in the upper Campanian Didymoceras stevensoni zone in the Rock River Formation of Wyoming.

Solenoceras differs from Oxybeloceras in possessing constrictions and in having the early growth stages in the form of a gently curved shaft that originates from a tiny initial coil.

OCCURRENCE: Solenoceras has been found in the Western Interior only in the middle and upper Campanian. It occurs in the zones of Baculites gregoryensis and Baculites scotti in the Pierre Shale in South Dakota; in the Didymoceras stevensoni zone in the Pierre Shale in Colorado, Wyoming, and Montana; in the Didymoceras nebrascense zone in the Bearpaw Shale in Montana and in the Pierre Shale in South Dakota and Colorado; in the Exiteloceras jenneyi zone in the Pierre Shale in Montana, South Dakota, and Colorado; in the same zone in the Mancos Shale in Colorado; and in the Baculites reesidei zone in the Pierre Shale in Colorado, Wyoming, and Montana. Solenoceras has been recorded from Arkansas, Texas, Tennessee, Mississippi, Georgia, and California, as well as from Spain? (Martinez, 1982), Italy (Giudici and Pallini, 1993), Belgium (Kennedy, 1993), Angola (Haughton, 1925), Nigeria? (Zaborski, 1985), Israel? (Lewy, 1969), Egypt? (Hamama and Kassab, 1990), and Japan (Matsumoto and Morozumi, 1980).