aligned almost laterally but move to a more anterior location during growth. The preabdomen also lengthened, increasing the overall length of the ophisthosoma. The swimming legs also became narrower and the telsons shorter and broader (though in E. tetragonophthalmus and E. henningsmoeni the telsons changed from being angular in juveniles to larger and more rounded in adults). All these changes are believed to be a result of the respiratory and reproductive requirements of adults. Paleoecology Members of Eurypterus existed for a relatively short time, yet they are the most abundant eurypterids found today. They flourished between the Late Llandovery epoch (around 432 million years ago) to sometime during the Přídolí epoch (418.1 million years ago) of the Silurian period. A span of only around 10 to 14 million years. During this period, the landmasses were mostly restricted to the southern hemisphere of the Earth, with the supercontinent Gondwana straddling the South Pole. The equator had three continents (Avalonia, Baltica, and Laurentia) which slowly drifted together to form the second supercontinent of Laurussia (also known as Euramerica, not to be confused with Laurasia). The ancestors of Eurypterus were believed to have originated from Baltica (eastern Laurussia, modern western Eurasia) based on the earliest recorded fossils. During the Silurian, they spread to Laurentia (western Laurussia, modern North America) when the two continents began to collide. They rapidly colonized the continent as invasive species, becoming the most dominant eurypterid in the region. This accounts for why they are the most commonly found genus of eurypterids today. Eurypterus (and other members of Eurypteroidea), however, were unable to cross vast expanses of oceans between the two supercontinents during the Silurian. Their range were thus limited to the coastlines and the large, shallow, and hypersaline inland seas of Laurussia. They are now only known from fossils from North America, Europe, and northwestern Asia, cratons that were the former components of Laurussia. While three species of Eurypterus were purportedly discovered in China in 1957, the evidence of them belonging to the genus (or if they were even eurypterids at all) is nonexistent. No other traces of Eurypterus in modern continents from Gondwana are currently known. Eurypterus are very common fossils in their regions of occurrence, millions of specimens are possible in a given area, though access to the rock formations may be difficult. Most fossil eurypterids are the disjointed shed exoskeleton (known as exuviae) of individuals after