Placenticeras

Placenticeras; Temporal range: Late Cretaceous
	Placenticeras meeki
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Mollusca
Class:	Cephalopoda
Subclass:	†Ammonoidea
Order:	†Ammonitida
Family:	†Placenticeratidae
Genus:	†Placenticeras; Meek, 1870
Synonyms
	Diplacmoceras

Placenticeras is a genus of ammonites from the Late Cretaceous. Its fossils have been found in Asia, Europe, North and South America.

Taxonomy

Placenticeras, named by Fielding Bradford Meek, 1870, is the type genus for the Placenticeratidae, a family that is part of the Hoplitoidea, a superfamily of the Ammonitida.

Description

Placenticeras sp. ammolite, Bearpaw Formation. At the Royal Tyrrell Museum of Palaeontology.

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 auxiliary elements, with saddles and lobes that are much frilled.

Species

Species list according to [1]:

Placenticeras bidorsatum
Placenticeras costatum
Placenticeras cumminsi
Placenticeras fritschi
Placenticeras grossouvrei
Placenticeras intercalare
Placenticeras kolbajense
Placenticeras maherndli
Placenticeras mediasiaticum
Placenticeras memoriaschloenbachi
Placenticeras meeki
Placenticeras orbignyanum
Placenticeras paraplanum
Placenticeras placenta
Placenticeras polyopsis
Placenticeras pseudoplacenta
Placenticeras semiornatum
Placenticeras syrtale (syn. Stantonoceras pseudocostatum)
Placenticeras tamulicum
Placenticeras vredenburgi
Placenticeras whitfieldi
P. costatum, Pierre Shale Formation, South Dakota
P. placenta with mosasaur bite marks
P. meeki showing sutures
P. intercalare ammolite, Bearpaw Formation, Alberta, Canada
P. whitfieldi with mosasaur bite marks
Placenticeras sp. showing sutures. Pierre Shale, Upper Cretaceous; Meade County, South Dakota (USA)

References

Arkell et al., 1957, Mesozoic Ammonoidea, Treatise on Invertebrate Paleontology Part L. Geological Soc. of America, Univ of Kansas Press. R.C. Moore, (Ed)
W. A. Cobban and Hook, S. C. 1983 Mid-Cretaceous (Turonian) ammonite fauna from Fence Lake area of west-central New Mexico. Memoir 41, New Mexico Bureau of Mines&Mineral Resources, Socorro NM.
W. A. Cobban and Hook, S. C. 1979, Collignoniceras woollgari wooollgari (Mantell) ammonite fauna from Upper Cretaceous of Western Interior, United States. Memoir 37, New Mexico Bureau of Mines&Mineral Resources, Socorro NM.
Discovering Fossils: How to Find and Identify Remains of the Prehistoric Past (Fossils & Dinosaurs) by Frank A. Garcia, Donald S. Miller, and Jasper Burns
Placenticeras in the Paleobiology Database

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