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

ammonoid Ammonoids are a group of extinct marine mollusc animals in the subclass Ammonoidea of the class Cephalopoda. These molluscs, commonly referred to as ammonites, are more closely related to living coleoids (i.e., octopuses, squid and cuttlefish) ...

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'' (or ''TIP'') published by the Geological Society of America and the University of Kansas Press, is a definitive multi-authored work of some 50 volumes, written by more than 300 paleontologists, and co ...

, 1957 Part L. They are the: *

Stephanoceratidae Stephanoceratidae is a family of planulate and coronate ammonites within the Stephanoceratoidea.Arkell, Kummel, and Wright, 1957. Mesozoic Ammonoidea; Treatise on Invertebrate Paleontology, Part L, Mollusca 4. Shells are evolute so that all whorl ...

Kosmoceratidae Kosmoceratidae is an extinct ammonite family from the Callovian (Middle Jurassic) to Early Cretaceous. Kosmoceratidae are probably the most polymorphic groups of Jurassic ammonites. These ammonoids have a more or less tabulate venter, with lat ...

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 of the Jurassic Period, and it span ...

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) ammonites, commonly with evolute shells with strong ribbing that typically divides about mid flank before crossing the ven ...

. 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 formal and systematic written discourse on some subject, generally longer and treating it in greater depth than an essay, and more concerned with investigating or exposing the principles of the subject and its conclusions."Treat ...

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