Cladoceramus

Cladoceramus is an extinct genus of fossil marine pteriomorphian bivalves that superficially resembled the related winged pearly oysters of the extant genus Pteria. They lived in the Santonian stage of the Late Cretaceous.

Description
Adult shells of Cladoceramus are small to very large size (more than 1 m in length). Many species with fine, discrete, juvenile ornamentation on umbo, consisting of closely and evenly to subevenly spaced raised concentric growth lines without rugae. Posterior auricle well-defined, triangular, separated from disc by auricular sulcus; a post-umbonal sulcus occurs in some species, as do very small anterior auricles ("ears").

Biostratigraphic significance
The first appearance of the species Cladoceramus undulatoplicatus marks the beginning of the Santonian stage.

Distribution
Fossils of the genus have been found in:
 * Matulla Formation, Egypt
 * United States
 * Forbes Shale, California
 * Smoky Hill Shale, Niobrara Formation, Colorado and New Mexico
 * Austin Chalk, Texas
 * Mancos Shale, Wyoming