Eurypterus- Sea ScorpionWhen: Late Silurian ~ 430-420 million years ago  Where: In ancient relativel

Eurypterus- Sea ScorpionWhen: Late Silurian ~ 430-420 million years ago  Where: In ancient relatively shallow seas, swimming over what is today North America and Europe. They are very common in the eastern US, and are the state fossil of New York. What: Eurypterus is the most well known member of the Eurypterida. Okay that probably didn’t help much! These animals are arthropods (insects, spiders, crustaceans, etc) and in the group that incudes the horseshoe crabs, spiders, and scorpions. They are not actually scorpions, though they are closely related to them.  Like a lot of living arthropods, they grow by successive molting and can become very large, in fact the largest arthropods known were eurypterids! Most fossil are small, just a few centimeters, but the largest one is over 4 feet (120cm) long from head to tail tip! They moved both by swimming though the water with their large paddles arms and walking on the substrate with their smaller legs.  They were carnivorous and most likely at the top of the food chain in their day - jawed fishes were just starting to appear. Its possible the evolution and migration of these fishes is what lead to the extinction of the sea scorpions.  -- source link

More pics about