Lytoceratina

Lytoceratinais asuborderofJurassicandCretaceousammonitesthat produced loosely coiled, evolute and gyroconic shells in which the sutural element are said to have complex moss-like endings.

Lytoceratina Temporal range:
Fossil shells ofLytoceras cornucopiafrom I sắc re (France), on display atGalerie de paléontologie et d'anatomie comparéein Paris
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Mollusca
Class:	Cephalopoda
Subclass:	†Ammonoidea
Order:	†Ammonitida
Suborder:	†Lytoceratina Hyatt,1899
Families
Lytoceratidae Arcuceratidae Bochianitidae Dactyloceratidae Derolytoceritidae Ectocentritidae Gaudryceratidae Nannolytoceratidae Pleuroacanthitidae Protetragonitidae Tetragonitidae

Morphologic characteristics

Shells are generally evolute, with all whorls exposed and touching, some are gyroconic with whorls separated by a space. Whorl sections vary from subcircular to narrowly compressed. The venter, or outer rim, is generally broadly arched but in some is keeled. Sides are either smooth or ribbed. Sutural elements are typically complex, referred to in the literature as moss-like, with adventious and secondary subdivisions. Saddle endings tend to be rounded but usually not phylloid, lobes tend to be more jagged with thorn-like endings. Aptychi are single valved and concentrically striated (Anaptychus)

Derivation and phylogeny

The Lytoceratina, which constitute a suborder within the Ammonitida, are derived from the TriassicUssuritidaeorDiscophyllitidae,families belonging to thePhylloceratina,or both (which would make them polyphyletic). They in turn gave rise to the main body of JurassicAmmonitinaand to the CretaceousAncyloceratina.

Included Families

Twelve families have been described of which theLytoceratidaedominate. The Lytoceratidae also have the longest range, from the Lower Jurassic to the Cenomanian stage in the Upper Cretaceous.

References

• Arkell et al., Mesozoic Ammonoidea,Treatise on Invertebrate Paleontology,Part L, Mollusca 4; Geol Soc of America & Univ. Kansas press, 1957.
• The Paleobiology Database - Lytoceratina4/05/10