Name: Diplomoceras ‭(‬double horn‭)‬.
Phonetic: Dip-lo-mo-seh-rass.
Named By: Hyatt‭ ‬-‭ ‬1900.
Synonyms: Eudiplomoceras.
Classification: Animalia,‭ ‬Mollusca,‭ ‬Cephalopoda.
Species: D.‭ ‬cylindraceum,‭ ‬D.‭ ‬lambi,‭ ‬D.‭ ‬notabile.
Diet: Carnivore/Piscivore.
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.

       While 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 appears.‭
       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.

Further reading
-‭ ‬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.


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