There are over 20 known eurypterid families and some were formidable predators in the Paleozoic seas (one grew as long as 3 meters). Here in New York, our state fossil is Eurypterus remipes - a Silurian Period eurypterid shown below.
Turns out an ancient eurypterid trackway was recently discovered in Scotland (northeast Fife). The tracks were left on damp sand by a 2 meter monster called Hibbertopterus some 330 million years ago during the middle part of the Mississippian Period (Lower Carboniferous over there in Europe). A BBC news article on the find states that "The track consists of three rows of crescent shaped footprints on each side of a central groove." The animal was likely walking along a beach, dragging its tail (telson) to form the groove.
Fossil trackway on tilted sandstone bed (note hammer for scale)
Eurypterids may have had book lungs and could come out of the water occassionally, like horseshoe crabs (Limulus polyphemus) on Atlantic beaches today. Would have been a neat site to see. At the time, what we now know as the British Isles were near the equator and large areas were covered with equatorial swamps and riotous vegetation which later formed the coal deposits from which the Carboniferous Period derived its name.
The fossil trackway is along the coast in Scotland so it's in danger of weathering away. They're creating a reproduction of it in silicone rubber so it can be studied. It's a shame they can't save the actual slab.