Aipoceratoidea Hyatt 1884

Superfamily Aipoceratoidea Hyatt, 1884 Fig. 37 Diagnosis Superfamily of the suborder Solenochilina, in which the conch form ranges from gyroconic to nearly involute with extraordinarily high coiling rate. Whorl profile laterally compressed to weakly depressed. Included families Aipoceratidae Hyatt, 1884 (Early Carboniferous to Early Permian; Permian; 5 genera, 18 species). Solenochilidae Hyatt, 1893 (Early Carboniferous to Middle Permian; 2 genera, 36 species). Remarks A very apt characterisation of the superfamily Aipoceratoidea was given by Shimansky (1967: 39) (translated from Russian): “The origin of the peculiar Late Palaeozoic nautiloids, grouped in the superfamily Aipocerataceae and characterised by a smooth conch of various shapes, a ventral position of the siphuncle and an almost straight suture line, is not very clear. There seems to be no doubt about the unity of the group, even though its representatives differ greatly in the shape of their conchs. Some have conchs with completely free whorls (Aipoceras), others with touching whorls (Asymptoceras) and others with slightly overlapping whorls (Solenochilus). In most representatives, the shell rapidly increases in width and height, sometimes becoming almost spherical (Solenochilus, Acanthonautilus) and forming lateral ear-like projections (Fig. 37). American authors differentiate between the families Aipoceratidae and Solenochilidae, which we agree with, since both groups of genera (Asymptoceras, Aipoceras, Librovitschiceras, on the one hand, and Solenochilus, Acanthonautilus, on the other) are very different. There is no doubt that the former are closer to the ancestral forms, most likely Rutoceratidae, and the latter are descended from the former.” This is similar to what was given by Furnish & Glenister (in Kummel 1964) before: “Conch rapidly expanding, cyrtoconic to coiled, whorls rounded to flattened or possibly impressed dorsally; shell surface smooth to ribbed; modified mature aperture known in most forms; sutures nearly straight; siphuncle marginal and ventral; septal necks orthochoanitic on ventral surface and orthochoanitic to cyrtochoanitic on dorsal side.” The two families are characterised as follows: Aipoceratidae Hyatt, 1884. – Ancestral forms with a gyroconic conch; whorl profile usually laterally compressed (Fig. 38). Solenochilidae Hyatt, 1893. – Derived forms with a subinvolute or involute conch; whorl profile circular or depressed (Fig. 39).