Who ruled the Paleozoic seas? The Eurypterid did!

This is a 380 million year old sea scorpion or eurypterid (Eurypterus sp.) from New York state (left). It one of the thousands of specimens in the invertebrate paleontology collection at the Cincinnati Museum Center. Eurypterids were aquatic predators with paddle-like appendages and spiked claws used for catching prey. Their closest living relatives are the arachnids (spiders, harvestmen, mites and scorpions). Eurypterid fossils are found in Ohio and Kentucky and in many other locations in the Eastern United States and around the globe. Eurypterids are the state fossil of New York state and many fine specimens, like this one in the Cincinnati Museum Center collection, have been unearthed in that region.

Now, being only about 15-20 cm in length, this species may not be that imposing but other eurypterids grew to much larger size. Shown here is another eurypterid specimen in the Cincinnati Museum Center collection, Megalograptus ohioensis, collected in Ohio (right). This fossil dates to about 445 million years ago and consists only of the distal portion of the one of the claws or chelicerae, a little like a lobster claw or that of a modern terrestrial scorpion. This portion of the claw alone is about 2 cm wide and nearly 4 cm long. The spines on the claw likely used for grasping slippery prey items are clearly visible. This fragment obviously came form a much larger animal than the New York Eurypterus specimen, however, size variation in eurypterids doesn't stop here.

In a new paper by Simon Braddy, Markus Poschmann and Erik Tetlle available online in the journal Biology Letters the authors describe a new specimen of the eurypterid, Jaekelopterus rhenaniae. The fossil remains described in the Braddy et al. paper are from an animal nearly 2.5 m long, that's just over 8 feet in length. Not only is this is the largest eurypterid described to date it is the largest arthropod ever. The claws of J. rhenaniae alone were over 40 cm long and lined with long spines. The authors speculate that higher oxygen levels in the paleozoic seas may have contributed to the gigantic size of many arthropods during this time but a lack of large vertebrate predators like marine reptiles may have also been a factor as well because large eurypterids like these went extinct about the time we begin to see large marine reptiles in the fossil record.

Read more about this on NPR and listen to an interview with the authors of the study. Thanks to Brenda Hanke of Cincinnati Museum Center for help on this post.