What’s That Science? Eurypterids

Orchids? You can buy some of those at the nearest Home Depot. Squids? Most people have probably at least heard of calamari. But what on Earth is a eurypterid?

Well, it isn’t an organism you will find living on Earth any more. Eurypterids, also known as “sea scorpions,” were common underwater predators from about 470 to about 250 million years ago. Long before the rise of the dinosaurs, these chelicerates – relatives of modern-day spiders, scorpions, and horseshoe crabs – lived abundantly in a variety of aquatic habitats, preying upon fish, other arthropods, and each other. Some larger species could reach almost two meters in length – that’s longer than the average American is tall!

Eurypterids were diverse organisms. Some swam, some walked, some crawled and burrowed, and some did all of these things. This variety in lifestyle is clearly visible in the diversity of body plans eurypterids display in the fossil record; some have paddle-like limbs useful for swimming, while others had appendages better suited for walking or gathering food.

Sea scorpions seem to have lived in a wide variety of habitats, ranging from solidly marine ocean floor to freshwater lakes and rivers to brackish estuaries and bays (where freshwater meets and mixes with saltwater). Alas, eurypterids reached their peak during the Silurian Period, around 440 – 420 million years ago, when plants were still in the early stages of moving onto land. If you want to see a eurypterid these days, you’ll have to look into the fossil record. Eurypterids are most commonly found in North American and European fossil assemblages; the rest of the world has a fairly sparse record of these creatures.

Why should you care about eurypterids? Well, who wouldn’t care about a two-meter-long sea scorpion that could have been swimming around a lake or river near you – if you had lived 250 million years ago, that is!


Benton, Michael J., and David A. T. Harper. Introduction to Paleobiology and the Fossil Record. Chichester, West Sussex: Wiley-Blackwell, 2009. Pp 375-8; 482-6; 550. Provided information on eurypterids, and on the colonization of land by plants.

McDowell, M. A., C. D. Fryar, C. L. Ogden, K. M. Flegal. “Anthropometric reference data for children and adults: United States, 2003-2006.” National Health Statistics Reports: No 10. Hyattsville, MD: National Center for Health Statistics (2008). http://www.cdc.gov/nchs/data/nhsr/nhsr010.pdf – see pages 14 and 16. Provided height statistics of men and women in the United States.

Selden, P. A., “Autecology of Silurian Eurypterids.” Special Papers in Palaeoecology Issue 32, 39-54 (1984). Provided information on ecology of eurypterids. http://www.paulselden.net/uploads/7/5/3/2/7532217/autecology.pdf

Tetlie, O. Erik. “Distribution and dispersal history of Eurypterida (Chelicerata).” Palaeogeography, Palaeoclimatology, Palaeoecology Vol. 252, Issue 3-4: pp. 557-574 (2007). Provided information on distribution of eurypterid fossils. http://dx.doi.org/10.1016/j.palaeo.2007.05.011


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