Hibbertopterus is a hibbertopterid eurypterid merostomate arthropod from the Middle Devonian-Mississippian of the United Kingdom, Belgium, the United States of America, Ireland, Czech Republic, and South Africa. It was officially named in 1959 by Erik Norman Kjellesvig-Waering. Alongside its semi-distant relative, Stylonurus, it was a unique eurypterid, as well as one of the largest, rivaling Pterygotus in size.
Hibbertopterus looked more like a horseshoe crab than the generic eurypterid. It had a large, rounded cephalothorax, mid-sized eyes, a pair of arms bearing blades, 3 pairs of walking legs, and a mid-sized tail ending in a spear-like telson. Its body would have been covered in a hard, chitinous exoskeleton.
Hibbertopterus was a predator, feeding on small invertebrates by sifting through the seafloor and catching them with the blades on it arms. As well as this, it would sometimes settle for detritus suspended in the water.
Like Stylonurus, Hibbertopterus did not have a pair of paddles for swimming like older eurypterids did, relying on its legs for walking and its tail for swimming. Unlike most eurypterids, it only truly had 6 legs, and its tail was not that long compared to the tails of other eurypterids. In general, Hibbertopterus lived at the bottom of rivers, swamps, and freshwater lakes, ravaging carcasses and using its bladed arms to catch small invertebrates. A parallel trackway indicates that it was able to crawl out of the water and onto dry land, much like modern horseshoe crabs.