''Placenticeras meeki'' is an
ammonite
Ammonoids are a group of extinct marine mollusc animals in the subclass Ammonoidea of the class Cephalopoda. These molluscs, commonly referred to as ammonites, are more closely related to living coleoids (i.e., octopuses, squid and cuttlefish) ...
species
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
from the
Late Cretaceous
The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', the ...
. These cephalopods were fast-moving
nektonic
Nekton or necton (from the ) refers to the actively swimming aquatic organisms in a body of water. The term was proposed by German biologist Ernst Haeckel to differentiate between the active swimmers in a body of water, and the passive organisms t ...
carnivores. They mainly lived in the American Interior Basin (
Western Interior Seaway
The Western Interior Seaway (also called the Cretaceous Seaway, the Niobraran Sea, the North American Inland Sea, and the Western Interior Sea) was a large inland sea that split the continent of North America into two landmasses. The ancient sea, ...
).
Description
Shells of this species could reach a diameter of about . They are discoidal, involute and compressed. Whorls are stout and rounded to diameter of 3 millimeters. The surface of fossils is usually covered by opalized nacre (
ammolite
Ammolite is an opal-like organic gemstone found primarily along the eastern slopes of the Rocky Mountains of North America. It is made of the fossilized shells of ammonites, which in turn are composed primarily of aragonite, the same mineral co ...
).
Etymology
The name honours
Fielding Bradford Meek
Fielding Bradford Meek (December 10, 1817 – December 22, 1876) was an American geologist and a paleontologist who specialized in the invertebrates.
Biography
The son of a lawyer, he was born in Madison, Indiana. In early life he was in bu ...
.
References
Ammonites* J.B. Reesid
A comparison of the genera Metaplacenticeras Spath and Platcenticeras MeekProfessional Paper - United States Geological Survey
*Sepkoski, Jac
Sepkoski's Online Genus Database – Cephalopodes
Placenticeratidae
Late Cretaceous ammonites
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