Eurypterids, or ‘sea-scorpions’ are an extinct group of chelicerates: the group containing the terrestrial arachnids (such as spiders and scorpions) and the aquatic ‘merostomes’ (represented today solely by the horseshoe crabs). They bear a gross-morphological resemblance to scorpions (hence the informal name) but, in being aquatic, may have shared more in common with horseshoe crabs. They inhabited the waters of the Paleozoic Era and were typically scavengers or predators. Most eurypterids were quite small and unremarkable, but some genera, such as Pterygotus and Jaekelopterus grew to incredible sizes; the latter reached an estimated 2.5m (8’ 2”) and is still the world’s largest-known arthropod.

Described today in BMC- Evolutionary Biology is the oldest-yet-described eurypterid Pentecopterus decorahensis and we've got lead author Dr James Lamsdell, Yale University, to introduce us to the eurypterids and to discuss the significance of this new genus.