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Eurypterid - Sea Scorpion Facts and Information - The Details

Eurypterids, or "Sea Scorpions" are an order of ancient arthropods that lived in the Paleozoic era. These formidable Paleozoic predators appeared in the Ordovician and became extinct in the great Permian mass extinction. They seem to have reached their peak in the Silurian.

Eurypterids are not Crustaceans. The Eurypterid order belongs to the Chelicerata superclass. This class includes Horseshoe crabs, scorpions, and arachnids. Although they may be related to Scorpions, they are not scorpions, and are only called "Sea Scorpions" due to the scorpion like tail found on many of the Eurypterid genera.

Most Eurypterids inhabited very shallow brackish and fresh water environments, and some may have been able to walk on land. Their bodies were made of many segments and joints. Most Eurypterids were under 10" in length, but some genera, such as Pterygotus and Jaekelopterus could reach lengths of over 7 feet, and may have been the largest arthropods to ever live.

Eurypterids have a nearly global distribution, but are rare as complete fossils. There are only a few places on Earth were whole Eurypterid Fossils can be regularly found (New York and Ontario in North America). As a result, many type specimens are fragments, therefore, a number of genera and species may be nomen dubium or junior synonyms. As a result, the actual number of genera is uncertain, with publications reporting anywhere from 40 to 80 genera. The most well known Eurypterid is probably Eurypterus rempise, the state fossil of New York.

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Sea Scorpions vs Real Scorpions

Sea Scorpions are not related to Scorpions. They just have a similar appearance.

True Scorpions appeared during the Silurian. The first ones seem to have been aquatic. These aquatic Scorpions can be found alongside Eurypterids in certain strata, such as the Phelps waterlime in the Fiddlers Green formation in New York.

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Fossil Occurence of Eurypterids

Eurypterids have a nearly global distribution, but they are usually found as fragments. There is, however, an Upper Silurian rock unit in New York and Ontario that have exquisitely preserved Eurypterids. This rock unit is called the Bertie group.

In this group, there are several Eurypterid "colonies" or "pools" where fossil Eurypterids are common and exquisitely preserved. These pools are called the Otisville Basin, the Pittsford Pool, the Herkimer Pool, and the Buffalo Pool. The latter two pools are more remarkable. The Herkimer Pool is in Herkimer County, NY, and the Buffalo Pool is near Buffalo and extends into Ontario.

Both of these Eurypterid pools were thought to be either shallow salt flats or tidal flats, where bodies and/or molts of Eurypterids living nearby washed up. These molts naturally accumulated in shallow depressions, called windrows, in the tidal flats.

The windrows at the fossil sites look like concoidal, or plate like, depressions in the Dolomite rock. To find Eurypterids, one must find natural fractures running through the concoidal depressions and correctly break them open to reveal the windrows. Usually the Eurypterid or Eurypterid pieces are centered neatly in the windrow.

By far, the best Eurypterid fossils on Earth have come from Allan Langheinrich's Quarry (Lang's Quarry) which is situated on top of the Herkimer Pool.

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Eurypterid Body Morphology

Eurypterids have a distinct body shape. They have a "U" shaped head followed by a series of 12 articulated segments called tergites. Below that is a tail, which is called the telson.

The body is divided into three main sections: the prosoma, the mesosoma, and the metasoma. The head is called the prosoma. It contains the Eurypterid's compound eyes and a pair of tiny eyes called ocelli. The prosoma also has appendages, such as walking legs, pinchers, and/or paddles. Some genera of Eurypterids have all walking legs and no paddles, while others have long pinchers.

Below the Eurypterid's head is the body. It is called the mesosoma, which is made from a series of tergites. The last body section is called the metasoma, which contains the telson, or tail. The telson can have many shapes depending on the Eurypterid genera. It is most often either stinger shaped or shaped like a paddle.

Eurypterus remipes had four pairs of walking legs, one pair of swimming legs, and a stinger like telson. Below is a diagram of Eurypterus remipes.

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Eurypterid Trackways - Including the Worlds Largest Eurypterid Track

Although complete Eurypterids are rare, tracks from these arthropods have been found in various places. Some notable discoveries include tracks from the early Devonian of Germany (Poschmann 2010), and a huge carboniferous trackway from Fife, Scotland (made by a ~1.6 meter Eurypterid). Other places include Australia, and various places in the United States, including Washington and Pennsylvania.

The Eurypterid trackway imaged here was excavated from a Carboniferous outcropping in Elk County, Pennsylvania. It was discovered in 1983 and is possibly the world's largest Eurypterid trackway. This trackway has been assigned to a Eurypterid called Palmichnium kosinskiorum, which is estimated to be approximately 7.5 feet long. This track is now displayed in the Carnegie Museum of Natural History.

Eurypterid trackways all look very similar, they have sets of 3 impressions on both the left and right sides (6 legs), and usually a tail imprint running down the center. The tail imprint in the imaged trackway is visible, but faint. Eurypterid tracks were probably laid down in very shallow water.

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Pterygotid: The Largest Sea Scorpion. Fierce Predator or Scavanger? New Evidence

Reaching lengths of over 2 m, Pterygotids are amung the largest sea scorpions to ever live. A Jaekelopterus specimen has been found that is slightly larger than Pterygotids.

These animals are amung the largest arthropods to ever exist! Robust mouthparts, long claws, forward facing eyes, along with their sheer size caused most people to assume it was a fierce predator; possibly one of the fiercest arthropod predators of all time! Just look at the image (An image of one of the largest Pterygotids ever found is just below this paragraph).

However, this view has recently changed. Research done by R. P. Anderson, et al. show they may have been a scavenger after all. The team developed and used new imaging technology along with a new mathematical analysis to reconstruct the visual capability of a Pterygotid and then compared it with the visual capability of other small Eurypterid species.

They found Pterygotids have far worse eyesight than other Eurypterids. In fact, all arthropod predators living today have much better eyesight. Pterygotids eyesight actually falls within the range of scavengers and not predators! The team concludes Pterygotids could have been large nocturnal scavengers.

So, it may have looked like a vicious predator, but this new research shows it may have, in fact, been a huge scavenger!

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Recommended Books and Items:

A Sea without Fish: Life in the Ordovician Sea of the Cincinnati Region (Life of the Past)
Life of the Past series: Richard Arnold Davis, David L. Meyer
Copyright 2009, Indiana University Press

This book gives a comprehensive view of life in the Ordovician seas. This wonderful introduction to the geology and paleontology of life in Ohio 450 million years ago is full of illustrations. If you have ever wondered what exactly the Ordovician of Ohio, New York, and the surrounding states looked like, this is your window!

Eurypterid Swimming Wall Decal - 24 Inches W x 17 Inches H - Peel and Stick Removable Graphic
If your child likes fossils and paleontology and wants a change from the standard dinosaur wall decales, this would make a great gift!

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Eurypterid Fossil Examples:

E. remipes, E. lacustris, and Pterygotus sp.

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Eurypterus remipes (DeKay, 1825)
Sea Scorpion

This is one of the more common Eurypterids found in New York

This large specimen is missing the telson and pretelson section of the body. It also is missing one swimming paddle, but has part of a walking leg preserved.

Formation:Bertie Dolestone of the Fiddler's Green Formation, Phelps Waterlime
Age:Upper Silurian ~410 m.y.o.
Location:Herkimer County, N.Y.
Size:3 3/8"(86mm)
Trip:New york Eurypterid Trip

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This positive and negative of a smaller specimen has a complete body, but all of the appendages are missing.

Formation:Bertie Dolestone of the Fiddler's Green Formation, Phelps Waterlime

Age:Upper Silurian ~410 m.y.o.
Location:Herkimer County, N.Y.
Size:3 1/8"(79mm)
Trip:New york Eurypterid Trip

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These two parts may be of the same specimen. They have the correct number of tergites, and the size is correct. On the computer, the two parts crop together nearly perfectly.

Formation:Bertie Dolestone of the Fiddler's Green Formation, Phelps Waterlime
Age:Upper Silurian ~410 m.y.o.
Location:Herkimer County, N.Y.
Size: 2 14"(57mm)
Trip:New york Eurypterid Trip

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This faint and tiny, yet remarkable, specimen has all of it's walking legs and swimming legs attached.

Formation:Bertie Dolestone of the Fiddler's Green Formation, Phelps Waterlime
Age:Upper Silurian ~410 m.y.o.
Location:Herkimer County, N.Y.
Size:3/4"(19mm)
Trip:New york Eurypterid Trip

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Here is a small specimen with the metasoma and a paddle missing. It has parts of two walking legs preserved.

Formation:Bertie Dolestone of the Fiddler's Green Formation, Phelps Waterlime
Age:Upper Silurian ~410 m.y.o.
Location:Herkimer County, N.Y.
Size:1 1/4"(32mm)
Trip:New york Eurypterid Trip

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Eurypterus lacustris (Harlan)
Sea Scorpion

This species of Euryperid may be synonymous with E. rempise, or a subspecies of E. rempise

This is a prosoma and one tergite of a Eurypterid.

Formation:Bertie Dolestone of the Fiddler's Green Formation, Phelps Waterlime
Age:Upper Silurian ~410 m.y.o.
Location:Ridgemount (Walker Brothers) Quarry, Fort Erie, Ontario
Size:1/2"(13mm)
Trip:Ontario TRIP

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Pterygotus sp.
Sea Scorpion

Pterygotus looks different than many Eurypterids. One notable difference is the telson (tail). Instead of a stinger like telson it has a swimming paddle.
Pterygotus were also the largest of the Eurypterids. A cast of one of the worlds largest is shown at the top of this page.

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Links to Eurypterid Sites

Langs Fossils
The Langheinrich Fossil Preserve. They are committed to the preservation and study of Eurypterus remipes


EURYPTERIDS.NET
An awesome website devoted to Sea Scorpions

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References / Works Cited

R. P. Anderson, V. E. McCoy, M. E. McNamara, D. E. G. Briggs. (2014) What big eyes you have: the ecological role of giant pterygotid eurypterids. Biology Letters, 10 (7): 20140412 DOI: 10.1098/rsbl.2014.0412

Markus Poschmann, Simon J. Braddy. (2010) Eurypterid trackways from Early Devonian tidal facies of Alken an der Mosel (Rheinisches Schiefergebirge, Germany). Palaeobiodiversity and Palaeoenvironments 90(2):111-124

J. Waddington, D. M. Rudkin, J. A. Dunlop. (2015) A new mid-Silurian aquatic scorpion - one step closer to land? Biology Letters, Jan;11(1):20140815. DOI: 10.1098/rsbl.2014.0412