Oxynoticeratidae

Oxynoticeratidae Temporal range: Late Jurassic PreЄ Є O S D C P T J K Pg N
Scientific classification
Kingdom:	Animalia
Phylum:	Mollusca
Class:	Cephalopoda
Subclass:	†Ammonoidea
Order:	†Ammonitida
Superfamily:	†Psilocerataceae
Family:	†Oxynoticeratidae Hyatt, 1875

Oxynoticeratidae is a family of true ammonites (order Ammonitida) from the Lower Jurassic. They are part of the superfamily Psilocerataceae, characterized by mostly involute, oxyconic shells with narrow venter and compressed, lanceolate whorl section. Suture is ammonitic. Ribbing is feeble, hardly functional and often absent.

The Oxynoticeratidae evolved rapidly. They developed shorter body chambers than in the ancestral Arietitidae, resulting in more stable floating positions. Their mostly smooth, knife-edge discoidal forms would have allowed for quick, though probably no sustained, movement through the water.

Oxynoticeratids have a broad, worldwide distribution but a narrow stratigraphic one, being known only from the Upper Sinemurian and Lower Pliensbachian, a span of some 4 or 5 million years during which their shells changed little in form.

References

• Arkell, et al, 1957. Mesozoic Ammonoidea. Treatise on Invertebrate Paleontology, Part L, pp. L240-L243. Geological Soc. of America and Univ. Kansas Press.
• Donovan & Callomon, 1981. Ammonoidea. [1]