Placenticeratidae is an extinct family of mostly Late Cretaceous ammonites (

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

order Ammonitida) included in the superfamily

Hoplitoidea Hoplitoidea, formerly Hoplitaceae, is a superfamily of mostly Upper Cretaceous ammonites comprising families united by a similar suture pattern with multiple similar elements that tend to decrease in size going toward the umbi ...

, derived from the Engonoceratidae by an increase in suture complexity. Placeticeratids are characterized by rather involute compressed shells of moderate to large size with narrow flat or grooved venters (outer rims), at least on early whorls. Most are rather smooth or weakly ornamented except for a few later forms in which the outer whorls are strongly tuberculate. The suture has numerous, including auxiliary and adventive, elements. Saddles and lobes are typically deep, narrow necked, and raggedly embayed. The Placenticeratidae had their beginning in the Late Albian stage at the end of the Early Cretaceous, starting with '' Hypengonoceras''. The type genus, '' Placenticeras'', appears later and is known from the upper Santonian to the lower Campanian of the Upper Cretaceous. The family has the longest duration of the Hoplitaceae, extending well into the Maastrichtian, the final stage of the Cretaceous period with the genus '' Hoplitoplacenticeras''.

References

Sources

*Arkell ''et al.'', 1957. ''Mesozoic Ammonoidea; Treatise on Invertebrate Paleontology, Part L (Ammonoidea)''. Geol. Soc. of America and Univ. Kansas Press. Ammonitida families Hoplitoidea Albian first appearances Maastrichtian extinctions {{Ammonitina-stub