Orthorhombisella

Orthorhombisella is a genus of small, extinct marine bivalve mollusks that lived during the Late Cretaceous period, approximately 99.6 to 66 million years ago. The genus is characterized by its orthorhombic shell shape, which is a distinctive feature among bivalves. The shells of Orthorhombisella are typically small, ranging from a few millimeters to a few centimeters in length, and are composed of calcite. The genus is known from fossil specimens found in marine sediments from various locations around the world, including Europe, North America, and Asia.

The taxonomy of Orthorhombisella is somewhat controversial, with some researchers classifying it as a separate genus within the family Orthorhombidae, while others consider it to be a junior synonym of the genus Orthorhombus. Despite this uncertainty, Orthorhombisella is an important fossil taxon for understanding the evolution of bivalve mollusks during the Late Cretaceous. Its orthorhombic shell shape is a unique adaptation that may have allowed it to occupy a specific ecological niche within its marine environment. Further study of Orthorhombisella fossils may provide additional insights into the diversity and evolution of bivalves during the Cretaceous period.