The holotype specimen of Millkoninckioceras Kummel 1963 is large, capping out at 135 mm in diameter. Ammonoids reached great sizes during the Mesaozic, but large coiled Nautaloids are rare. Most nautiloid macrofossils found in the Glenshaw Formation are about the diameter of a baseball or smaller, whereas rare significant examples can be double or larger the diameter.

The holotype has rounded ventrolateral and umbilical shoulders; in cross-section, it is a wide oval. The sutures are straight across the flank and center. There is no test (shell) preserved on the holotype.

Koninckioceras was renamed to Millkoninckioceras by Kummel (1963)

In a review of Koninckioceras, Kummel (1963) focuses on Hyatt’s (1884) declaration that deKonick’s (1851) specimen, Nautilus ingens, was the type for his new genus, Koninckioceras. Earlier, deKoninick named Ammonites ingens Martin 1809 as the type for his new genus, Nautilus ingens. Earlier still, Martin (1809) used the name Conchyliolithes (Nautilites) ingens for his specimen, not Ammonites ingens.

Conchyliolithes (nautilites) ingens Martin 1809
Conchyliolithes (nautilites) ingens Martin 1809

Shortly after deKoninick (1851) named Nautilus ingens, M’Coy (1855) assigned several specimens from the British Museum to Nautilus ingens Martin. He proposed that Nautilus pentagonus (Sowerby) be synonymized with Nautilus ingens Martin, an idea Foord (1891) agreed with. Yet, Foord cautioned setting N. ingens as the senior name because there was “much uncertainly” about that name.

Nautilus pentagonus Sowerby 1812
Nautilus pentagonus Sowerby 1812 (Plate 249)
Nautilus ingens—Plate 60, Figure 1 by deKoninick, 1851.

Later, Foord (1891) and Miller and Kemp (1947) agreed that deKoninick’s and Martin’s specimens were not conspecific. As a result, Miller and Kemp erected Koninckioceras konincki for Hyatt’s specimen of Koninckioceras. Since Kummel determined the type specimen of Hyatt’s K. konincki unrecognizable, he erected a new name, Millkoninckioceras, placing Miller and Kemp’s specimen of Koninckioceras konincki as the type species.

References

  • Foord, A. H., 1891, Catalogue of the fossil Cephalopoda in the British Museum (Natural History), Part 2, containing the remainder of the suborder Nautiloidea, consisting of the families Lituitidae, Trochoceratidae, and Nautilidae with a supplement. London, 407 pp.
  • Hyatt, A., 1884, Genera of fossil cephalopods. Proceedings of the Boston Society of Natural History, vol. 22, pp. 253-338
  • Koninick, L. G. de, 1878, Fauna du Calcaire Carbonifere de la Belgique; Premiere partie: Mus. Royale Hist. Nat. Belg. Ann., t. 2, pp. 1-152, pls. 1-31.
  • Kummel, B., 1963, Miscellaneous nautilid type species of Alpheus Hyatt. Bulletin of the Museum of Comparative Zoology 128:325-368