Sephanoceratidae is a family of planulate and coronate ammonites

Ammonitina

The Ammonitina comprises a diverse suborder of ammonoid cephalopods that lived during the Jurassic and Cretaceous periods of the Mesozoic Era. They are excellent index fossils, and it is often possible to link the rock layer in which they are found to specific geological time periods.The shells of...

 within the Stephanocerataceae

Stephanocerataceae

Stephanocerataceae is a superfamily of middle Jurassic ammonoid cephalopods within the order Ammonitida containing diverse forms, generally with sharp ribbing and complex suture lines...

. (Arkell et al 1957) Shells are evolute so that all whorls are exposed and have strong ribbing that bifurcates, that is splits in two, on the flanks. Many have tubercles at the point of bifurcation. Whorl sections are generally subequant; the outer rim, or venter, commonly rounded (ibid)

The Sephanoceratidae are derived from the Otoitidae

Otoitidae

Otoidtidae: stephanoceratacean ammonitina from the early Middle Jurassic that begin as cadicones but become more planualte with age; derived from the Hammitoceratidae , probably through Erycites by way of Abbasites....

. Their fossils are found in upper Middle- and lower Upper Jurassic sediments.