List of Eurypterids - Phylogeny

Phylogeny

The cladogram presented here is simplified from a study by Tetlie. The most important phylogenetic breakdown is based on the two major innovations that characterise the evolution of the eurypterids. The most important was the transformation of the posteriormost prosomal appendage into a swimming paddle (as found in the clade Eurypterina). The second innovation was the enlargement of the chelicerae, (as found in the family Pterygotidae), allowing these appendages to be used for active prey capture.

75% of eurypterid species are eurypterines; this represents 99% of specimens. The superfamily Pterygotioidea is the most species-rich clade with 56 species, followed by the Adelophthalmoidea with 43 species; as sister taxa, they comprise the most derived eurypterids. Pterygotioidea includes the pterygotids, which are the only eurypterids to have a cosmopolitan distribution. This clade is one of the best supported within the eurypterids.

It has been suggested that the development of dermal armour in certain groups of jawless vertebrates (such as the Heterostraci and the Osteostraci) is in response to predation pressure by increasingly sophisticated eurypterid predators (specifically the pterygotids) although this has yet to be verified by detailed analysis. An increase in fish diversity is tied to a decline in eurypterid diversity in the Lower Devonian, although it is not thought that this represents competitive replacement; in fact, this is rare in the fossil record.