Jaekelopterus was a predatory aquatic arthropod of the order of eurypterids, often called sea scorpions. Its claws and compound eyes indicate it was active and powerful with high visual acuity, most likely an apex predator in the ecosystems of Euramerica. Fossils have been discovered from roughly 400 million years ago, during the Early Devonian. There are two known species: the type species J. rhenaniae from brackish to fresh water strata in the Rhineland, and J. howelli from estuarine strata in Wyoming. Based on isolated fossil remains from the Klerf Formation of Germany, J. rhenaniae has been estimated to have reached a size of around 2.3–2.6 metres (7.5–8.5 ft), making it the largest arthropod ever discovered. J. howelli was much smaller, reaching 80 centimetres (2.6 ft) in length. In overall appearance, Jaekelopterus was similar to other pterygotid eurypterids, with enlarged pincers and forelimbs. The genus was named for German paleontologist Otto Jaekel, who described the type species. (Full article...)