Pentecopterus decorahensis: Upper Iowa River Giant Sea Scorpion Fossil

by DerdriuMarriner

Pentecopterus decorahensis, Decorah’s winged warship, is a 470,000,000-year-old Upper Iowa River Crater giant sea scorpion found in 2010 and named in 2015.

Decorah’s winged warships are super-big, super-old sea scorpions

Twenty-first century Earthlings generally associate scorpions with:
• stinging tails;
• Tequila bottles.

They typically behave less cautiously and more confidently when threats of poisons, reactions, toxins, and venoms are contained or countered. But ancestral lines and fossil histories challenge any peace of mind achieved by canceling or controlling poisonous, toxic, venomous interactions through reconstructed scenarios of what once was and therefore may be once more.

For example, paleobiologists and paleogeologists describe two prehistorically unsettling scenarios of:
• a 5.6-kilometer (3.48-mile) crater attesting to a 250-meter (820.21-foot) meteorite impact 443,800,000 to 485,400,000 years ago under what is now Decorah’s Upper Iowa River;
• 150 470,000,000-year-old fossil pieces enshrining 20 giant sea scorpions with mature head-to-tail bodies 1.7 meters (5.58 feet) long.

Thus far Pentecopterus decorahensis is oldest fossil of Eurypterida order, known informally as sea scorpions:

reconstruction of Eurypterus remipes: fossil of extinct genus of sea scorpions first eurypterid fossil discovery -- found in central New York in 1818; named in 1825; adopted as New York State Fossil in 1984.
Smithsonian National Museum of Natural History's National Fossil Hall, Washington DC
Smithsonian National Museum of Natural History's National Fossil Hall, Washington DC

Decorah’s winged warships brave low-level, low-oxygen, low-salt waters


One good discovery encourages another. The discovery since 2010 of 5,354 specimens -- with 6.6% as eurypterid remains -- follows that in 2008 of the Decorah impact crater sustaining Winneshiek Shale’s suspected copper-, nickel-, platinum-rich, 27-meter-thick (88.58-foot) formation. Paleobiologists give the name eurypterid -- from the ancient Greek words εὐρύς (eurús-,  “wide”) and πτερόν (pterón, “wing”) -- to extinct, wide swimming-appendaged relatives of such modern arthropods -- from combining ἄρθρον (árthron, “joint”) and πούς (poús, “foot”) -- as:

  • harvestmen, mites, scorpions, solifuges, spiders, ticks;
  • horseshoe crabs;
  • lobsters.

The collection has as its most revelatory fossils giant sea scorpion adults and juveniles with respectively 75- to 100-centimeter-long (29.53- to 39.37-inch-long) and 10- to 15-centimeter-long (3.94- to 5.91-inch-long) limbs.


Modern-day relatives of Pentecopterus decorahensis include horseshoe crabs, which, originating 445,000,000 years ago (445 mya) in same geologic period, Ordovician, also share same class, Merostomata. ~

Atlantic Horseshoe Crab (Limulus polyphemus): ca. 1908 color print illustration by Heinrich Harder (June 2, 1858 – February 5, 1935).
Wilhelm Bölsche, Tiere der Urwelt (1916): illustrations first issued in series of prehistoric creature cards by Reichardt Cocoa Company in 1908.
Wilhelm Bölsche, Tiere der Urwelt (1916): illustrations first issued in series of prehistoric creature cards by Reichardt Cocoa...

Decorah’s winged warships cannot fossilize metastoma and side-eyes


The collection indicates survival of bivalve-, fish-, invertebrate-feeding top predators in brackish, oxygen-poor, shallow, tide-influenced, warm waters. Its paleoartists and paleontologists judge as super-accurate reconstructive descriptions and illustrations. Specimen removals by bin-angled chisels, steel periodontal probes, and water indeed keep together all molted bristles, follicles, scales, and structures except:

  • brain-covering, frontal prosomal shields;
  • lateral (side-located) eyes;
  • mouth-proximitous metastoma elevation;
  • ocelli (head-top “little eyes”).

They nevertheless leave scientific procedural doors open and revision-friendly through:

  • dry, normal-lit image production by Adobe Illustrator CS5 on OSX-run MacBook Pro, Adobe Photoshop CS5, Canon EOS 60D digital camera and EF-S60mm f/2.8 Macro USM fixed lens, Huion L42 LED light pad, Leica DFC240 digital camera and MZ16 stereomicroscope;
  • University of Iowa-housed specimen collections.


Decorah’s winged warships do not battle not-yet-existing dinosaurs


Images and information from discoverers Derek Briggs, James Lamdell, Huaibao Liu, Robert McKay, and Brian Witzke make clear eco-system functions of Decorah’s winged warships -- named for ancient Greek 50-oared battleships -- as:

  • descendants of 485,400,000- to 541,000,000-year-old Cambrian ancestors or explosive Mid-Ordovician radiators until 252,170,000 years ago;
  • Laurentian predators outcompeting Avalonian and Gondwanian bottom-feeders.

They need inspire nothing excepting:

  • appreciation for excellent analysis;
  • inspiration for future research;
  • relief over giant sea scorpion-free North American existences.

But they offer cause to speculate upon unmourned eco-system demises of Decorah’s winged warship, seemingly sustainable in:

  • angled, prey-grasping, sharp-spined fore-limbs;
  • balance-functioning, non-stinging, spikey tail half total length;
  • elongated, multi-claw-protected, helmet-shielded head;
  • hardy exoskeleton;
  • narrow, swimmer-streamlined body;
  • paddle-like, sensory bristle-covered rear-limbs.


Fossils Show Big Bug Ruled the Seas 460 Million Years Ago

Published on YouTube on September 2, 2015 by The Red Phoenix ~ URL:



My special thanks to talented artists and photographers/concerned organizations who make their fine images available on the internet.


closeup of setae (bristles) covering ventral prosimal integument (= underside of anterior segment of tough outer protective layer) of Pentecopterus decorahensis

scale bar = 1 millimeter
scale bar = 1 millimeter

Sources Consulted


Borenstein, Seth. 31 August 2015. “Fossils Show Big Bug Ruled the Seas 460 Million Years Ago.” MSN > News. Retrieved September 3, 2015.

  • Available @

Borenstein, Seth. 1 September 2015. “Iowa Fossils Show Giant Sea Scorpion Was Dominant Predator of Its Time.” The Globe and Mail > News > World. Retrieved September 3, 2015.

  • Available @

De Pastino, Blake. 31 August 2015. “’Incredibly Bizarre’ Giant Sea Scorpion Discovered in Iowa Fossil.” Western Digs > Dinosaurs & Ancient Life > Fossils. Retrieved September 3, 2015.

  • Available @

Feltman, Rachel; and Kaplan, Sarah. 1 September 2015. “’Bizarre’ Giant Sea Scorpion May Have Been the World’s First Big Predator.” The Washington Post > Speaking of Science. Retrieved September 3, 2015.

  • Available @

Ferreira, Becky. 31 August 2015. “This Prehistoric Sea Scorpion Was the Size of a Person.” Motherboard. Retrieved September 3, 2015.

  • Available @

Geggel, Laura. 1 September 2015. “’Bizarre’ Human-size Sea Scorpion Found in Meteorite Crater.” MSN > News > LiveScience. Retrieved September 3, 2015.

  • Available @

Haines, Lester. 1 September 2015. “Giant Sea Scorpion Which Prowled Ancient Oceans Revealed.” The Register > Science. Retrieved September 3, 2015.

  • Available @

Hays, Brooks. 1 September 2015. “Scientists Discover Ancient Six-Foot-Long Sea Scorpion.” UPI > Science News. Retrieved September 3, 2015.

  • Available @

Kaplan, Sarah. 1 September 2015. “Scientists Find Earth’s First Big Predator: A Terrifying Giant Sea Scorpion.” The Sydney Morning Herald > Environment > Animals. Retrieved September 3, 2015.

  • Available @

Lamdell, James C.; Briggs, Derek E.G.; Liu, Huaibao P.; Witzke, Brian J.; and McKay, Robert M. 31 August 2015. “The Oldest Described Eurypterid: A Giant Ordovician (Darriwilian) Megalograptid from the Winneshiek Lagerstätte of Iowa.” BMC Evolutionary Biology 15:169. Retrieved September 3, 2015.

  • Available @

Martin, Sean. 1 September 2015. “Fossilised ‘Giant Sea Scorpion’ Discovered in Iowa. International Business Times > Science. Retrieved September 3, 2015.

  • Available @

Payne, Ed. 1 September 1, 2015. “Met the Scorpion’s Prehistoric, Bigger, Badder Cousin.” CNN > U.S. Retrieved September 3, 2015.

  • Available @

Pratt, Sara E. 7 July 2013. “Iowa Impact Crater Confirmed.” Earth > Magazine. Retrieved September 3, 2015.

  • Available @

The Associated Press. 1 September 2015. “Giant Sea Scorpion May Have Been Earth’s 1st Big Predator.” CBC News > Technology & Science. Retrieved September 3, 2015.

  • Available @

Winston, Joel. 31 August 2015. “Giant ‘Sea Scorpion’ Fossil Discovered.” EurekAlert! > Public Releases. Retrieved September 3, 2015.

  • Available @

Yale University. 1 September 2015. “Meet Pentecopterus, a Giant Sea Scorpion: Predator from Prehistoric Seas.” Science Daily > Releases. Retrieved September 3, 2015.

  • Available @


Decorah Crater: 470- million-year-old meteorite crater concealed beneath bedrock and, at depth of 50+ feet below Upper Iowa River's bottom, Winneshiek Shale Lagerstätte sediments, which yield extraordinarily well-preserved fossils such as Pentecopterus ~

3-Dimensional view of Decorah, Iowa and the Upper Iowa River. Scene is looking due north. ~ Crater, known as Decorah Impact Structure, was discovered during 2008-2009 mineral survey by Iowa Geological and Water Survey.
3-D Perspective View of Decorah Impact
3-D Perspective View of Decorah Impact
the end which is also the beginning
the end which is also the beginning

Gold Scorpio Zodiac Charm, 10k by Charm America ~ 10k Gold Charm with Rhodium Center ~ Available now via Amazon

More than a zodiac symbol for late October - late November births, Scorpius is a large Southern Hemisphere constellation honoring a brave scorpion elevated to the sky by Zeus ~ P. decorahensis emerges as prehistoric warrior (predator) of the seas.
scorpion themed products

Decorah, Iowa - Panoramic Map: Available as Art Print and as Premium Giclée Print ~ Available now via AllPosters

1870 bird's-eye view of Decorah, Iowa with Iowa River flowing through and Upper Iowa River (site of discovery of Pentecopterus decorahensis) on outskirts
Decorah, Iowa - Panoramic Map

Me and my purrfectly purrfect Maine coon kittycat, Augusta "Gusty" Sunshine

Gusty and I thank you for reading this article and hope that our product selection interests you; Gusty Gus receives favorite treats from my commissions.
DerdriuMarriner, All Rights Reserved
DerdriuMarriner, All Rights Reserved
Updated: 08/02/2021, DerdriuMarriner
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DerdriuMarriner on 09/03/2015

blackspanielgallery, Considering all the development worldwide, it's amazing that anything still gets found!

blackspanielgallery on 09/03/2015

It is amazing what fossils can be found.

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