Inoceramus

Inoceramus is an extinct genus of fossil saltwater clams. These were marine clams that ressembled the winged pearly oysters of the extant taxon, the genus Pteria. In other words they were pteriomorphian bivalves.

Inoceramus species lived worldwide during the Cretaceous period. Many examples are found in the Pierre shale of the Western Interior Seaway in North America. Inoceramus can also be found abundantly in the Cretaceous Gault Clay that underlies London. Other locations for this fossil include Vancouver Island, British Columbia, Canada; Texas, Tennessee, California and Alaska, USA; Spain, France, and Germany.

The clam had a thick shell paved with "prisms" of calcite deposited perpendicular to the surface, which gave it a pearly luster in life. Most species have prominent growth lines which appear as raised semicircles concentric to the growing edge of the shell. Paleontologists suggest that the giant size of some species was an adaptation for life in the murky bottom waters, with a correspondingly large gill area that would have allowed the animal to cope with oxygen-deficient waters.

The number of valid species is disputed. The taxonomy of the inoceramids is also disputed, with genera such as Platyceramus sometimes classified as subgenus within Inoceramus.