Some had two paddles for swimming. They may have swum on their backs. Eurypterids date from the early Paleozoic Era , arising during the Ordovician period, over 400 million years ago. Many are found from the Silurian period. They went extinct in the Permian mass extinction.
Eurypterids are the state fossil of New York.
It isn't known whether or not it had a crest. The type species is S. koerneri . Secernosaurus was named by Brett-Surman in 1979. Most fossils are found in exposed sedimentary rock. They had woody stems studded with dried out leaf bases.