Discophyllitidae are discoidal, generally evolute

Phylloceratina The Phylloceratina comprise a suborder (biology), suborder of Ammonoidea, ammonoid cephalopods, belonging to the Ammonitida, whose range extends from the Lower Triassic to the Upper Cretaceous. Shells of the Phylloceratina are generally smooth w ...

from the Upper Triassic, derived from the

Ussuritidae Ussuritidae are ancestral, Triassic, Phylloceratina characterized by generally smooth, discoidal, evolute shells with rounded venters and little or no ornamentation and by sutures with primitive monophyllitic saddles with a single terminal branch ...

, in which the principal saddles of the suture have bifurcated or trifurcated endings, described as being di- or triphyllic. Discophyllitid shells are rather similar to those of the ancestral Ussuritidae and are distinguished primarily by the more complex suture. The Discophyllitidae provided the source for the Jurassic

Phylloceratidae Phylloceratidae is the predominant family of the Phylloceratina with some 15 or more genera found in rocks ranging from the Lower Jurassic to the Upper Cretaceous. Members of the Phylloceratidae are characterized by smooth, involute shells with v ...

and Juraphyllitidae. Four genera are recognized and described.

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 ...

Part L Mollusca 4, Ammonoidea, 1957

Discophyllitid genera

*'' Discophyllites'': Discophyllitids in which the first lateral saddle of the suture is asymmetrically monophyllic, like those of the Ussuritidae. The remaining are characteristic of the family. *'' Rhacophyllites'': Discophyllitidae in which the first lateral saddle of the suture is diphyllic and adjacent lateral saddles are diphyllic or triphillic. *'' Tragorhacoceras'': Discophyllitidae with peripheral ribs on the outer whorl and with large leaflets in the sutural saddles. *'' Trachyphyllites'': a discophyllitid with sigmoidal growth lines and about six ribs or flares per whorl; suture less phylloid than in other genera of the family. ''Discophyllites'' and ''Rhacophyllites'' have their beginnings in the early Late Triassic. Both are found in Europe, the Himalayas, and on Timur; ''Discophyllites'' in California and Alaska as well. ''Discophyllites'' is the more primitive and ancestral genus. ''Rhacophyllites'' is slightly more evolved with its more developed suture. ''Tragorhacoceras'' and ''Trachyphyllites'' are known from the middle Late Triassic, ''Tragorhacoceras'' from the Alps and Sicily, ''Trachyphyllites'' from the island of Timur. Both result from further, but different, evolutionary developments within the Discophyllitidae.

References

Ammonitida families Phylloceratina Triassic ammonites Carnian first appearances Early Jurassic extinctions {{Ammonitida-stub