Grypoceratoidea, Hyatt, 1900

New family Korn & Hairapetian (in press)

Fig. 21 View Fig

Diagnosis

Family of the superfamily Grypoceratoidea with a usually discoidal, subinvolute conch. Whorl profile in the adult stage weakly compressed or weakly depresses; flanks and venter usually separated by a distinct ventrolateral shoulder, venter more or less concave. Umbilical margin usually subangular or angular, rarely rounded; umbilical wall steep, often flattened. Ornament usually consisting of fine growth lines. Septum simple in shape, concavely domed; suture line depending on whorl profile with shallow to V-shaped external lobe and shallow lateral lobe (from Korn & Hairapetian in press: 14).

Included genera

Pseudotitanoceras Shimansky, 1965 (Wuchiapingian; 1 species).

New genus B to be described by Korn & Ghaderi (in press) (Changhsingian; 2 species).

New genus A to be described by Korn & Hairapetian (in press) (Wuchiapingian; 3 species).

New genus B to be described by Korn & Hairapetian (in press) (Wuchiapingian; 2 species).

Remarks

As Korn & Hairapetian (in press) will outline, grypoceratids with a whorl profile characterised by a concave venter, a pronounced ventrolateral shoulder with skid-like extensions, strongly convergent flanks and an angular umbilical margin occurred iteratively in the Late Carboniferous and Late Permian. It may be discussed whether they are phylogenetically related or belong to independent evolutionary lineages.

The Late Permian species are morphologically closely related; they are characterised by a rather late ontogenetic transformation from a juvenile growth stage with a rounded or flattened venter to an adult stage with a concave venter. Furthermore, the Late Permian species have rather stout conchs (ww/dm between 0.40 and 0.55), whereas the conchs of the Late Carboniferous species are usually much slenderer (ww/dm between 0.30 and 0.35). The umbilical margin is more pronounced in the Late Permian genera. These are probably good reasons to assume that the Late Permian species evolved independently of the Late Carboniferous species.

The family Ocunautilidae is characterised by a transformation of the originally broadly rounded venter into a more or less concave venter in the middle ontogenetic stage. The new family can therefore easily be derived from the family Domatoceratidae , some species of which also show a similar transformation. In addition to the modification of the venter, some members of the family Ocunautilidae show a narrowing of the umbilicus and a subangular or angular shape of the umbilical margin.