Placenticeras is an ammonite

Ammonite

Ammonite, as a zoological or paleontological term, refers to any member of the Ammonoidea an extinct subclass within the Molluscan class Cephalopoda which are more closely related to living coleoids Ammonite, as a zoological or paleontological term, refers to any member of the Ammonoidea an extinct...

 genus

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 from the Late Cretaceous

Late Cretaceous

The Late Cretaceous is the younger of two epochs into which the Cretaceous period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous series...

. Its fossil

Fossil

Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

s have been found in Asia, Europe, North and South America.

Taxonomy

Placenticeras, named by Meek, 1870, is the type genus for the Placenticeratidae

Placenticeratidae

The Placenticeratidae is a family of mostly Late Cretaceous ammonites included in the superfamily Hoplitaceae, derived from the Engonoceratidae by an increase in suture complexity....

, a family that is part of the Hoplitaceae

Hoplitaceae

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 umbilicus, at the inner edge of any whorl, and which are typically in a straight line...

, a superfamily of the Ammonitida

Ammonitida

The Ammonitida is an order of more highly evolved ammonoid cephalopods from the Jurassic and Cretaceous time periods, commonly with intricate ammonitic sutures....

.

Description

Placenticeras has a very involute shell with slightly convex sides and a very narrow venter. Side are smooth or with faint sinuous ribs. Early whorls have umbilical tubercles that in later whorls appear higher on the sides. Earlier whorls normally have lower and fine upper ventrolateral clavi. Ornament weakens in the adult and the last whorl may be smooth. The suture is with numerous adventitious and autxiliary elements, with saddles and lobes that are much frilled.