Evolution and systematics

There are numerous limpet taxa in the Paleozoic fossil record, however none possesses unique characteristics that convincingly place these taxa within the order Patellogastropoda. The earliest patellogastropod verified by shell microstructure is from the Triassic of Italy, but it is in the Late Cretaceous and Tertiary periods that many of the living higher taxa have their first occurrences in the fossil record.

Phylogenetic analysis places the patellogastropods at the base of the gastropod tree as the sister taxon to all other gastropods. Although all living patellogastropods are limpets with cap-shaped shells, it is likely that like other living limpets they are descended from coiled snails. However, possible ancestors have not yet been identified in the fossil record.

The patellogastropods are divisible into two major suborders, the Patellina and Acmaeina. The Patellina includes the families Patellidae and Nacellidae. The Acmaeina includes the families Lepetidae, Acmaeiadae, and Lottiidae. Because of their simple shell morphology and anatomy, classifications of the patellogastropods have tended to underestimate their diversity. The application of molecular techniques is providing help in resolving the evolutionary history of this group, and systematic and nomenclatural revisions are certain.

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