Waeringopteridae

Waeringopteridae is a family of eurypterids, an extinct group of aquatic arthropods. The Waeringopteridae is the only family classified as part of the superfamily Waeringopteroidea, which in turn is classified within the infraorder Diploperculata in the suborder Eurypterina. The earliest known member of the group, Orcanopterus, has been recovered from deposits of Katian (Late Ordovician) age and the latest known surviving member, Grossopterus, has been recovered from deposits of Siegenian (Early Devonian) age. The name Waeringopteridae is derived from the type genus Waeringopterus, which is named in honor of eurypterid researcher Erik N. Kjellesvig-Waering.

Waeringopterid fossils are very rare and the family only contains five known species classified in three different genera (Waeringopterus, Orcanopterus and Grossopterus). Four of these species are from the ancient continent of Laurentia, with the only species known from outside of it being a Devonian species recovered from Germany. It is thus considered likely that the group originated in Laurentia before spreading to Germany during the Devonian. As the fossil record of the group is extremely poor, little is known of the morphology of the taxa within the group.

Although confirmed by phylogenetic analyses as monophyletic, and routinely used within eurypterid taxonomy, "Waeringopteroidea" and "Waeringopteridae" were not formally published clades until 2025, the names instead deriving from a 2004 thesis by O. Erik Tetlie. Some researchers referred to the group more formally as the "waeringopteroid clade" rather than as the superfamily "Waeringopteroidea", pending a formal publication. However, the group name was formalised in a 2025 overview paper of eurypterid taxonomy.