''Zetoceras'' is an extinct

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 ...

cephalopod A cephalopod is any member of the molluscan Taxonomic rank, class Cephalopoda (Greek language, Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral symm ...

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

from the

suborder Order () is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and recognized ...

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 ...

that lived during the Early and Middle

Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately 143.1 Mya. ...

in what is now Europe, and is included in the (family)

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 ...

. ''Zetoceras'' has a compressed involute shell with a very small umbilicus. The suture is phylloid, as for the suborder, with tall primary sutural elements. Saddles commonly have tetraphyllic endings. ''Zetoceras'' is considered by some (Wright ''et al'', 1996) to be a subgenus of '' Phylloceras''. The two are very similar except that the saddle endings in '' Phylloceras'' split in three rather than in four as in ''Zetoceras''.

References

* Wright, Calloman, and Howarth. 1996; Cretaceous Ammonoidea.

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 ...

L(4)
The Paleobiology Database ''Zetoceras'' entry
Ammonitida Sinemurian first appearances Middle Jurassic extinctions {{Ammonite-stub