hold them while they used their chelicerae to rip off pieces small enough to swallow. Young individuals may also have fallen prey to cannibalism by larger adults. Eurypterus were most probably marine animals, as their remains are mostly found in intertidal shallow environments. The concentrations of Eurypterus fossils in certain sites has been interpreted to be a result of mass mating and molting behavior. Juveniles were likely to have inhabited nearshore hypersaline environments, safer from predators, and moved to deeper waters as they grew older and larger. Adults that reach sexual maturity would then migrate en masse to shore areas in order to mate, lay eggs, and molt. Activities that would have made them more vulnerable to predators. This could also explain why the vast majority of fossils found in such sites are molts and not of actual animals. The same behavior can be seen in modern horseshoe crabs. Respiration Examinations of the respiratory systems of Eurypterus have led many paleontologists to conclude that it was capable of breathing air and walking on land for a short amount of time. Eurypterus had two types of respiratory systems. Its main organs for breathing were the book gills inside the segments of the mesosoma. These structures were supported by semicircular 'ribs' and were probably attached near the center of the body, similar to the gills of modern horseshoe crabs. They were protected under platelike appendages (which actually formed the apparent 'belly' of Eurypterus) known as Blatfüsse. These gills may have also played a role in osmoregulation. The second system are the Kiemenplatten, also referred to as gill-tracts. These oval-shaped areas within the body wall of the preabdomen. Their surfaces are covered with numerous small spines arranged into hexagonal 'rosettes'. These areas were vascularized, hence the conclusion that they were secondary breathing organs. The function of the book gills are usually interpreted to be for aquatic breathing, while the Kiemenplatten are supplementary for temporary breathing on land. However, some authors have argued that the two systems alone could not have supported an organism the size of Eurypterus. Both structures might actually have been for breathing air and the true gills (for underwater breathing) of Eurypterus have yet to be discovered. Eurypterus, however, were undoubtedly primarily aquatic. Ontogeny Juvenile Eurypterus differed from adults in several ways. Their carapaces were narrower and longer (parabolic) in contrast to the trapezoidal carapaces of adults. The eyes are