Arietitidae is a family of true ammonites that make up part of the superfamily

Psiloceratoidea Psiloceratoidea is a superfamily of Early Jurassic Ammonoidea, ammonoid cephalopods proposed by Alpheus Hyatt, Hyatt in 1867, assigned to the order Ammonitida. They were very successful during Hettangian and Sinemurian. Last of them, family Cym ...

, named after the type genus '' Arietites''. They comprise medium-size to large or gigantic genera which in general are strongly ribbed, tuberculate in some, with keeled or grooved and keeled venters, and well differentiated ammonitic sutures. The aptycus is single valved with a shiny, concentrically striated surface. Arietitidae dominated

Lower Jurassic The Early Jurassic Epoch (in chronostratigraphy corresponding to the Lower Jurassic Series) is the earliest of three epochs of the Jurassic Period. The Early Jurassic starts immediately after the Triassic–Jurassic extinction event, 201.3 Ma&nb ...

Sinemurian In the geologic timescale, the Sinemurian is an age (geology), age and stage (stratigraphy), stage in the Early Jurassic, Early or Lower Jurassic epoch (geology), Epoch or series (stratigraphy), Series. It spans the time between 199.5 ±0.3 annu ...

ammonites, worldwide, extending into the lower

Pliensbachian The Pliensbachian is an age of the geologic timescale and stage in the stratigraphic column. It is part of the Early or Lower Jurassic Epoch or Series and spans the time between 192.9 ±0.3 Ma and 184.2 ±0.3 Ma (million years ago). The Plie ...

. The Arietitidae may have their origin in the Schlotheimiidae if not directly from the

Psiloceratidae Psiloceratidae is an extinct family of cephalopods belonging to the ammonite subclass. Description The Psiloceratidae are evolute, smooth or with blunt primary ribbing. The venter is rounded and generally smooth, in some feebly keeled. Sutures a ...

, and is the probably source for the Oxynoticeratidae.

References

* * Donvan, D.T. and Callomon, J.H. 1981, Classification of the Jurassic Ammonitina., in The Ammonoidea, The Systematics Association Special Volume 18. {{Taxonbar, from=Q4790516 Ammonitida families Psiloceratoidea Sinemurian first appearances Early Jurassic extinctions