Named By: Hyatt - 1900.
Classification: Animalia, Mollusca, Cephalopoda.
Species: D. cylindraceum, D. lambi, D. notabile.
Size: Large individuals had shells up to 2 meters across (4 meters or more when you account for the shell winding).
Known locations: Worldwide distribution with fossil site locations including Antarctica - Lopez de Bertodano Formation, Santa Marta Formation. Australia - Korojon Calcarenite Formation, Miria Formatio. Belgium - Craie de Ciply Formation, Maastricht Formation. Chile - Quiriquina Formation, Rio Blanco Formation, Santa Ana Formation. Denmark - Danish White Chalk Formation. France - Craie de Valognes Formation, Les Vignes Formation. Greenland. Japan - Senpohshi Formation. Netherlands - Maastricht Formation. Russia. South Africa. Spain - Vallcarga Formation. Tunisia. USA, Alabama - Prairie Bluff Formation;, Alaska - Kaguyak Formation, Matanuska Formation; California - Moreno Formation; Mississippi - Prairie Bluff Formation; Texas - Corsicana Marl Formation, Escondido Formation.
Time period: Campanian to Maastrichtian of the Cretaceous.
Fossil representation: Well over a hundred specimens known from shells with varying degrees of preservation.
most ammonites had shells that wound tightly in a spiral,
Diplomoceras was more unusual. The shells starts
out straight before
making a U-bend, then growing out back the other way before making
another U-bend around. The shell then continues growing again until
making yet another U-bend and turning back on itself, extending all
the way back beyond the extent of the shell before the head opening
The exact reason why Diplomoceras grew such an unusual shell is unknown. One reason could be so that species of Diplomoceras could recognise one another apart from the other species of ammonites that were swimming in the oceans at this time. A more streamlined shell may have also allowed for faster swimming similar to that of earlier orthocones, and may have allowed for a greater chance of predator evasion from the large shell crushing mosasaurs such as Proganthodon and Globidens that were common in the Late Cretaceous seas. This might also explain why Diplomoceras did not appear until the Campanian period of the late Cretaceous.
Whatever the reason why Diplomoceras grew such an unusual shell, the genus was clearly very successful. So far fossils of Diplomoceras have been found very common in Antarctica and Australia, but are also known from the Americas, Europe, Africa and also Japan, which combined with the Australian and Antarctic fossils suggest that Diplomoceras were common across most of the world’s oceans, until finally vanishing in the KT extinction at the end of the Cretaceous.
- The Upper Cretaceous cephalopod fauna of Graham Land. - Falkland Islands Dependencies Survey Scientific Reports 3:1-60. - L. F. Spath - 1953.
- Late Cretaceous ammonites from Seno Skyring-Strait of Magellan area, Magallanes Province, Chile. Journal of Paleontology 46(4):520-532. - A. Lahsen & R. Charrier - 1972.
- Late Campanian-Maastrichtian ammonite fauna from Seymour Island (Antarctic Peninsula). The Paleontological Society Memoir 18:1-59. - C. E. Macellari - 1986.
- Maastrichtian heteromorph ammonites from the Carnarvon Basin, Western Australia. - Alcheringa 16:133-170. - R. A. Henderson, W. J. Kennedy & K. J. McNamara - 1992.
- Discovery of a remarkably complete specimen of the giant cephalopod Diplomoceras maximum from the Late Cretaceous of Seymour Island, Antarctica. - Antarctic Journal of the United States, Vol. 30 Issue 5, p9. - William J. Zinsmeister & Anton E. Oleinik - 1995.
- Observations on the systematics, geographic and stratigraphic distribution and origin of Diplomoceras cylindraceum (Defrance, 1816). - Annals of The South African Museum 110: 171-198. - Herbert Christian Klinger & William James Kennedy - 2003.