Pentecopterus

Pentecopterus is a genus of eurypterid, an extinct group of aquatic arthropods. Fossils have been registered from the Darriwilian age of the Middle Ordovician period, as early as 467.3 million years ago. The genus contains only one species, P. decorahensis, that is the oldest known eurypterid, surpassing other Ordovician eurypterids, such as Brachyopterus, in age by almost 9 million years. The generic name derives from the penteconter, a warship from ancient Greece, and the suffix -pterus, which means "wing" and is often used in other genus of eurypterids. The specific name refers to Decorah, Iowa, where Pentecopterus was discovered. The genus is classified as part of the Megalograptidae family of eurypterids, a family differentiated from other eurypterids by the possession of two or more pairs of spines per podomere on prosomal appendage IV, a reduction of almost all spines and the large exoskeletons with ovate to triangular scales. It is estimated that Pentecopterus had a length of , turning it into one of the largest eurypterids or arthropods ever discovered. However, Pentecopterus was overtaken by other eurypterids such as Jaekelopterus rhenaniae, the largest known arthropod with . A replica of the eurypterid was created for the National Geographic's "Strange Truth" program. The project had the help of James Lamsdell, one of the paleontologists who contributed to the description of Pentecopterus, who provided information and two illustrations. When it was finished, it was taken to the impact site where the original fossils were discovered. Pentecopterus is among the largest known arthropods, with the largest specimens having an estimated length of . With this size, it exceeds all other genera of the Megalograptidae. While fragmentary tergites have been suggested to indicate a length of for Megalograptus shideleri, they actually indicate a length of at most . Most Pentecopterus specimens would have had a total length of .