This cutie is one of my favourites. I imagine him wearing mittens but that, of course, is not the case at all.
This fellow is just under a centimetre in length but his cousins grew larger than a human. Eurypterids were the largest known arthropods to ever live.
The largest, Jaekelopterus, reached 2.5 meters (8.2 ft) in length — significantly larger than some of his very tiny cousins — most growing to less than 20 centimetres (8 inches) in length.
More commonly known as sea scorpions, the now-extinct eurypterids were arthropods that lived during the Paleozoic Era. We saw the first of their brethren during the Ordovician and the last of them during the End-Permian Mass Extinction Event. In between, they thrived and irradiated out to every niche within our ancient seas and many later forms survived and thrived in brackish and freshwater.
The group Arthropoda includes invertebrate animals with exoskeletons, segmented bodies, and paired joint appendages. Eurypterids had six sets of appendages. You can clearly see the segmented body on this cutie, which is one of the defining characteristics of arthropods. The first set was modified into pinchers which are used for feeding. The largest appendage visible in this fossil is a broad paddle that E. tetragonophthalmus used to swim.
This first eurypterid, Eurypterus remipes, was discovered in New York in 1818. It is an iconic fossil for this region and was chosen as the state's official fossil in 1984. An excellent choice as most of the productive eurypterid-bearing outcrops are within the state's boundaries. Most of the fossils we find from them, whether body fossils or trace fossils are from fossil sites in North America and Europe This is because the group lived primarily in the waters around and within the ancient supercontinent of Euramerica.
Only a handful of eurypterid groups spread beyond the confines of Euramerica and a few genera, such as Adelophthalmus — the longest lived of all known eurypterid genera — and the giant predatory Pterygotus, achieved a cosmopolitan distribution so we find their fossil remains worldwide today.
Interestingly, the type species, Pterygotus anglicus, was first through to be the remains of a massive fish by Swiss naturalist Louis Agassiz who described it in 1839 — hence the poorly chosen name Pterygotus, which translates to "winged fish. He did catch that embarrassing error five years later, but the name remains and will for all time.