4. Modern Analogs for the Study of Eurypterid Paleobiology

Eurypterids are extinct, chelicerate arthropods whose life habits might be elucidated through comparison with living analogs. There are at least two potential eurypterid analogs, xiphosurans and arachnids (specifically, scorpions). Eurypterids and scorpions share striking morphologic and structural similarities despite their different habitats (aquatic vs. terrestrial); eurypterids and xiphosurans share numerous morphological characters and an aquatic habit. Despite the physiological differences inherent between aquatic and terrestrial chelicerates, the similarities in the basic body plan suggest that eurypterids and scorpions faced similar functional challenges during ecdysis, but eurypterid feeding was probably more similar to that of xiphosurans. For studies on the mechanical strength and functional morphology of the eurypterid exoskeleton, Limulus is the closer analog. The choice of modern analog for other aspects of eurypterid paleobiology, including reproduction and whether eurypterids were active predators, is a matter of discussion. The lack of a single, clear eurypterid analog from among extant chelicerates may reflect that eurypterids occupied an ecological niche intermediate between xiphosurans and arachnids. The search for a modern analog for eurypterids, then, is not likely to yield a single model organism.