inoceramid

Inoceramids are an extinct family of marine bivalve mollusks known from the fossil record as the Inoceramidae. They lived in oceans from the Early Jurassic to the end of the Cretaceous, roughly 190 to 66 million years ago, with a broad geographic distribution that includes Europe, Asia, and the Americas.

Morphology and notable features: Inoceramids typically possessed large, thick shells with a rounded to elongated outline and a long hinge line. The surface ornamentation ranges from smooth to weakly ribbed, and the umbo is often prominent. Some Late Cretaceous forms grew to very large sizes, such as Platyceramus, whose shells could be substantial in width. The shells and internal features indicate they were sessile, benthic filter feeders anchored in soft substrates on the seafloor.

Ecology and life habits: As filter feeders living on the seabed, inoceramids inhabited a variety of marine environments from coastal shelves to deeper offshore settings. Their presence in many marine faunas makes them useful for understanding paleoecology and sedimentation in Jurassic and Cretaceous seas.

Distribution and significance: Inoceramids are among the more widespread and long-lasting bivalve groups of the Mesozoic, with abundant fossil records in many continents. They are especially important as biostratigraphic marker fossils for correlating Jurassic and Cretaceous strata across basins. The group largely disappears at the end of the Cretaceous, in step with the broader marine extinction at the Cretaceous–Paleogene boundary.