information:classification, structural:expansion
Devonian

Though the eurypterids continued to be abundant and diversify during the Early Devonian (for instance leading to the evolution of the pterygotid Jaekelopterus, the largest of all arthropods), the group was one of many heavily affected by the Late Devonian extinction. The extinction event, only known to affect marine life (particularly trilobites, brachiopods and reef -building organisms) effectively crippled the abundance and diversity previously seen within the eurypterids.

A major decline in diversity had already begun during the Early Devonian and eurypterids were rare in marine environments by the Late Devonian. During the Frasnian stage four families went extinct, and the later Famennian saw an additional five families going extinct. As marine groups were the most affected, the eurypterids were primarily impacted within the eurypterine suborder. Only one group of stylonurines (the family Parastylonuridae) went extinct in the Early Devonian. Only two families of eurypterines survived into the Late Devonian at all (Adelophthalmidae and Waeringopteridae). The eurypterines experienced their most major declines in the Early Devonian, during which over 50% of their diversity was lost in just 10 million years. Stylonurines, on the other hand, persisted through the period with more or less consistent diversity and abundance but were affected during the Late Devonian, when many of the older groups were replaced by new forms in the families Mycteroptidae and Hibbertopteridae.

It is possible that the catastrophic extinction patterns seen in the eurypterine suborder were related to the emergence of more derived fish. Eurypterine decline began at the point when jawless fish first became more developed and coincides with the emergence of placoderms (armored fish) in both North America and Europe.

Stylonurines of the surviving hibbertopterid and mycteroptid families completely avoided competition with fish by evolving towards a new and distinct ecological niche. These families experienced a radiation and diversification through the Late Devonian and Early Carboniferous, the last ever radiation within the eurypterids, which gave rise to several new forms capable of "sweep-feeding" (raking through the substrate in search of prey).