Koninckioceratoidea Hyatt, 1900

Superfamily Koninckioceratoidea Hyatt, 1900

Diagnosis

Superfamily of the suborder Temnocheilina , in which the whorl profile shows only minor changes during ontogeny. Conch usually discoidal, subinvolute to evolute. Whorl profile elliptical or almost circular throughout ontogeny. Adult whorl profile depressed oval. Without coarse sculpture. Suture line with shallow lobes and saddles; internal lobe absent or very shallow.

Included family

Koninckioceratidae Hyatt, 1900 (Early Carboniferous to Early Permian; 2 genera, 17 species).

Remarks

Depending on the researcher, the koninckioceratids are a group that has been variously assigned to different phylogenetic lineages. Shimansky (1957, 1962) accepted them as a family within the superfamily Lirocerataceae with the genera Koninckioceras Hyatt, 1884 , Lophoceras Hyatt, 1893 and Planetoceras Hyatt, 1893 . Later Shimansky (1967, 1979) elevated them to a superfamily within the suborder Rutoceratina , composed of a single family containing the three genera mentioned above.

Kummel (1963, 1964) accepted the koninckioceratids as a family within the Tainocerataceae and included eleven genera ( Millkoninckioceras Kummel, 1963 , Endolobus Meek & Worthen, 1865 , Foordiceras Hyatt, 1893 , Knightoceras Miller & Owen, 1934 , Subvestinautilus Turner, 1954 , Temnocheilus M‘Coy, 1844 and Tylodiscoceras Miller & Collinson, 1950 ); in other words, he combined the koninckioceratids and some of the temnocheilids into one taxon.

The superfamily Koninckoceratoidea is still poorly understood. There are several reasons for this, based on the general rarity and limited morphological inventory. Probably only one specimen of the type species of Millkoninckioceras is known, and other species, such as the Early Permian M. bibbi (Miller & Kemp, 1947) , can only be placed in the genus with reservations. Typically, Carboniferous and Permian nautiloids with a wide umbilicus and a depressed oval whorl profile have been assigned to Millkoninckioceras or morphologically similar genera.

The simple morphology ( Fig. 14 View Fig ) of the species within the group makes a phylogenetic reconstruction difficult. One hypothesis for their origin is that they descended from fully coiled species in the superfamily Trigonoceratoidea with initially slightly depressed juvenile conchs. However, in contrast to the other evolutionary lineages, there was no ontogenetic change in conch geometry with the formation of a ventrolateral shoulder or an umbilical margin in the koninckioceratids. Instead, members of the Koninckioceratoidea retained the simple juvenile morphology even in the intermediate and adult growth stages.

The species of the superfamily Koninckioceratoidea are distinguished from other Late Palaeozoic nautiloids by their very simple conch morphology, with a wide umbilicus and an unsculptured shell. In contrast to almost all other coiled nautiloids, the conch shows almost no ontogenetic changes.