Eothyrisoidea

Eothyrisoidea is an extinct superfamily of marine mollusks that lived during the Late Cretaceous period, approximately 100 to 66 million years ago. This group is characterized by its distinctive, flattened, and often asymmetrical shell, which is typically composed of aragonite. The superfamily includes several families, such as Eothyrisidae, which is the type family, and Eothyrididae, both of which are known for their unique shell morphologies.

The shells of Eothyrisoidea are often described as being "irregular" or "abnormal" in shape, with a wide variety of forms observed within the group. This diversity in shell shape is thought to have been an adaptation to different ecological niches and feeding strategies. Some species had shells that were highly modified for burrowing or crawling, while others had shells that were more streamlined for swimming.

The fossil record of Eothyrisoidea is well-represented, with numerous species described from various locations around the world, including North America, Europe, and Asia. These fossils provide valuable insights into the evolution of mollusks and the diversity of marine life during the Late Cretaceous.

Despite their distinctive appearance, the biology and ecology of Eothyrisoidea are not well understood. However, their unique shell morphologies and the diversity of their fossil record make them an important group for studying the evolution of mollusks and the history of marine life.