Stephanoceratoidea, formerly Stephanocerataceae, is a superfamily of middle- upper Jurassic

ammonoid Ammonoids are extinct, (typically) coiled-shelled cephalopods comprising the subclass Ammonoidea. They are more closely related to living octopuses, squid, and cuttlefish (which comprise the clade Coleoidea) than they are to nautiluses (family N ...

cephalopods within the order Ammonitida containing diverse forms, generally with sharp ribbing and complex suture lines. Aptychi are believed to be mostly granular (Granulaptycus) or concentrically ribbed on the surface (Praestriaptychus) (Arkell ''et al.'' 1957)

Morphologic variation

The shells of the Stephanoceratoidea, which determine the different included families, are highly variable in form. They are discoidal and evolute with all whorls exposed, spheroidal and involute with only the outer whorl showing, cadiconic with a deep umbilicus and broad ventral margin, and oxiconic with the ventral margin sharp. They are united by being generally sharply ribbed and by their complex suture lines with a dominant 1st lateral lobe and a well-developed umbilical lobe. (Arkell ''et al.'' 1957)

Taxonomy

Stephanoceratoidea contains five families according to Donovan ''et al.'' (1981), a reduction from the 11 listed in the

Treatise on Invertebrate Paleontology The ''Treatise on Invertebrate Paleontology,'' published from 1953–2007 by the Geological Society of America and the University of Kansas, then 2009–present by the University of Kansas Paleontological Institute, is a definitive multi-authore ...

, 1957 Part L. They are the: *

Stephanoceratidae Stephanoceratidae is a family of planulate and coronate ammonites within the Stephanoceratoidea Stephanoceratoidea, formerly Stephanocerataceae, is a superfamily of middle- upper Jurassic ammonoid cephalopods within the order Ammonitida cont ...

Kosmoceratidae Kosmoceratidae is an extinct ammonite family from the Callovian (Middle Jurassic) to Early Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final p ...

Otoitidae Otoidtidae: stephanoceratoid ammonitina from the early Middle Jurassic that begin as cadicones but become more planualte with age; derived from the Hammitoceratidae (Hildoceratoidea), probably through '' Erycites'' by way of '' Abbasites''. Sh ...

* Sphaeroceratidae *

Cardioceratidae Cardioceratidae is an extinct ammonite family belonging to the superfamily Stephanoceratoidea. These fast-moving nektonic carnivores lived during the Middle-Late Jurassic The Late Jurassic is the third Epoch (geology), epoch of the Jurassic P ...

The Pachyceratidae and Tulitidae included in the Stephanoceratoidea in the Treatise (1957) are reassigned to the

Perisphinctoidea Perisphinctoidea, formerly Perisphinctaceae, is a superfamily of Middle Jurassic (Bajocian) to Lower Cretaceous (Barremian) Ammonitina, ammonites, commonly with evolute shells with strong ribbing that typically divides about mid flank before cro ...

. The Macrocephalotidae and Mayaitidae of the Treatise are reduced to subfamilies within the Sphaeroceratidae, Macrocephalitinae and Mayaitinae, but still in the Stephanoceratoidea. The Clydoniceratidae and Thamboceratidae are combined as the Clydoniceratinae within the Hildoceratoid family Oppeliidae.

Phylogeny

According to Donovan ''et al'' (1981) the Stephanoceratidae and Otoitdae both have their origin in the Hildoceratoidea, in the Phymatoceratidae. The Otoitidae gave rise to the Sphaeroceratidae which gave rise to the Cardioceraticae, the Stephanoceratidae to the Kosmoceratidae, all within the Stephanoceratoidea. The Stephanoceratidae, accordingly, also gave rise to the Perisphinctidae, root stock of the Perisphictoidea. This differs from the older phylogeny of the

Treatise A treatise is a Formality, formal and systematic written discourse on some subject concerned with investigating or exposing the main principles of the subject and its conclusions."mwod:treatise, Treatise." Merriam-Webster Online Dictionary. Acc ...

Part L the Stephanoceratoidea are thought to be derived from the Hammatoceratidae (

Hildoceratoidea Hildoceratoidea, formerly Hildoceratacaea, is a superfamily of compressed or planulate ammonites, some tending to develop acute outer rims; generally with arcuate or sigmoidal ribs. Aptichus were found in place are double-valved.Arkell ''et al.' ...

) through the ancestral family, the Otoitidae which gave rise in the early Middle Jurassic to the Stephanoceratidae and Sphaeroceratidae, forming two main lineages. The Stephanoceratidae gave rise to the Thamboceratidae which in turn gave rise to the Clydoniceratidae. The Sphaeroceratidae gave rise to the Tulitidae which is the source for both the Macrocephalitidae and the Pachyceratidae. The Pachyceratidae lead to the Mayitidae, the Macrocephalitidae both the Kosmoceratidae and Cardioceratidae.

References

* Arkell ''et al.'', 1957. Mesozoic Ammononidea, Treatise on Invertebrate Paleontology, Part L, Mollusca 4. Geol. Soc. of America and Univ. Kansas press; R.C. Moore, Ed. p. L287 * Donovan, Callomon and Howarth, 1981. Classification of the Jurassic Ammonitina; Systematics Associatio
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{{Taxonbar, from=Q7608452 Ammonitida superfamilies Middle Jurassic first appearances Middle Jurassic extinctions