Palaeobiology of Silurian and Devonian eurypterids and scorpions

Arthropods (crustaceans, chelicerates, insects and myriapods) are the most diverse and abundant group of animals on our planet today, and have been since the Cambrian. The most diverse group of chelicerates during the Palaeozoic was the aquatic eurypterid s, with about 300 different species. They ranged from Ordovician to Permian, attaining maximum abundance and diversity in the Silurian. They include the largest arthropods ever to have evolved, predators over 2 meters long. Scorpions appeared in the Si lurian, but are much rarer, although they occur together with eurypterids. Even though eurypterids and scorpions were the major arthropod predators in a range of Palaeozoic communities, their palaeobiology is poorly known. They are very abundant in ce rtain environmental settings, but we do not know to what extent this is due to suitable conditions for preservation or habitat preference. Nor do we know what proportion of the fossils are moults versus carcases: large arthropods moult many times distort ing the abundance of predators. Extensive new discoveries of eurypterids and fossil scorpions in well documented sequences in New York, Indiana, and southern Ontario will be described in relation to their preservation, environmental context and associated fauna. Our understanding of changes in the diversity of these arthropods through time is now sufficient to allow the link between their evolution and changes in habitat to be analysed: both eurypterids and scorpions made major adaptive shifts to coloniz e fresh water and land respectively. New specimens will also allow outstanding questions about the position of eurypterids and scorpions within the chelicerates to be addressed.