Name: Diorocetus.
Phonetic: De-oh-roe-see-tus.
Named By: R.‭ ‬Kellogg‭ ‬-‭ ‬1968.
Classification: Chordata,‭ ‬Mammalia,‭ ‬Cetacea,‭ ‬Mysticeti.
Species: D.‭ ‬hiatus‭ (‬type‭)‬.‭ ‬D.‭ ‬chichibuensis,‭ ‬D.‭ ‬shobarensis.
Diet: Filter feeder.
Size: Total length about‭ ‬6‭ ‬meters long.
Known locations: Japan‭ ‬-‭ ‬Korematsu Formation and Nagura Formation.‭ ‬USA,‭ ‬Mayland‭ ‬-‭ ‬Calvert Formation,‭ ‬Calvert Beach Member,‭ ‬and Virginia‭ ‬-‭ ‬Calvert Formation,‭ ‬Plum Point Member.
Time period: Burdigalian through to the Serravalian of the Miocene.
Fossil representation: Several individuals represented by skulls and partial post cranial remains.

       Diorocetus was first named from fossils recovered from the United States by R.‭ ‬Kellog in‭ ‬1968,‭ ‬establishing the type species Diorocetus hiatus.‭ ‬Then in‭ ‬2003‭ ‬and‭ ‬2008‭ ‬respectively two new species,‭ ‬Diorocetus chichibuensis and Diorocetus shobarensis were named from fossils discovered in Japan.‭ ‬Out of these D.‭ ‬shobarensis seems to be the earliest with fossils roughly dated to the Burdigalian of the Miocene,‭ ‬while at the time of writing fossils for D.‭ ‬hiatus and D.‭ ‬chichibuensis are Langhian to Serravalian in age.‭ ‬Noted for having quite a slender skull for a mysticetid whale,‭ ‬Diorocetus was considered in a‭ ‬2009‭ ‬study by Beatty‭ & ‬Dooley to potentially be a bottom feeder as opposed to feeding in open water like the baleen whales that we know today.
       Diorocetus might have been preyed upon by large‭ ‘‬megatoothed sharks‭’ ‬such as C.‭ ‬chubutensis and of course the famous C.‭ ‬megalodon.‭

More information on these whales can be found on their respective pages; 1 - Pakicetus,
2 - Ambulocetus, 3 - Rodhocetus, 4 - Dorudon, 5, Brygmophyseter, 6 - Diorocetus.

Further reading
-‭ ‬A hitherto unrecognized Calvert Cetothere.‭ ‬Bulletin of the United States National Museum‭ ‬247‭(‬6‭)‬:133-161‭ ‬-‭ ‬R.‭ ‬Kellogg‭ ‬-‭ ‬1968.
-‭ ‬New cetothere‭ (‬Cetacea:‭ ‬Mysticeti‭) ‬from the Miocene Chichibumachi Group,‭ ‬Japan.‭ ‬-‭ ‬Bulletin of the Saitama Museum of Natural History‭ ‬20-21:1-10.‭ ‬Bulletin‭ ‬247:133-161.‭ ‬-‭ ‬K.‭ ‬Yoshida,‭ ‬T.‭ ‬Kimura‭ & ‬Y.‭ ‬Hasegawa‭ ‬-‭ ‬2003.
-‭ ‬Cladistic analysis and a revised classification of fossil and recent mysticetes.‭ ‬-‭ ‬Zoological Journal of the Linnean Society‭ ‬150:875-894.‭ ‬-‭ ‬M.‭ ‬E.‭ ‬Steeman‭ ‬-‭ ‬2007.
-‭ ‬Cetotheres from the early Middle Miocene Bihoku Group in Shobara District,‭ ‬Hiroshima Prefecture,‭ ‬West Japan.‭ ‬Miscellaneous Reports of the Hiwa Museum for Natural History‭ ‬49‭ (‬2‭) ‬:1-66.‭ ‬-‭ ‬H.‭ ‬Otsuka‭ & ‬Y.‭ ‬Ota‭ ‬-‭ ‬2008.
-‭ ‬Injuries in a Mysticete Skeleton from the Miocene of Virginia,‭ ‬With a Discussion of Buoyancy and the Primitive Feeding Mode in the Chaeomysticeti.‭ ‬-‭ ‬Jeffersoniana,‭ ‬Virginia Museum of natural History,‭ ‬20.‭ ‬Brian Lee Beatty‭ & ‬Alton C.‭ ‬Dooley Jr‭ ‬-‭ ‬2009.


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