Pentecopterus decorahensis: Upper Iowa River Giant Sea Scorpion Fossil

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.

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.

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.

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

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; Tuesday, January 1, 1980, 00:29: Ryan Somma, CC BY SA 2.0, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:Eurypterus_Smithsonian.jpg; Ryan Somma, CC BY SA 2.0, via Flickr @ https://www.flickr.com/photos/ideonexus/2238227210/in/set-72157603838941938/

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); one of 30 trading cards for Tiere der Urwelt (Animals of the Prehistoric World), illustrated by Heinrich Harder (June 2, 1858-February 5, 1935), written by Wilhelm Bölsche (January 2, 1861-August 31, 1939)
Tiere der Urwelt, Series 1a (1902-1916); Kakao-Compagnie Theodor Reichardt, Wandsbek, Hamburg, Northern Germany: Public Domain, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:Limulus.jpg

Pentecopterus could grow to almost six feet; the sea scorpion's narrow body supported a long head shield and large, prey-grasping limbs.
artist's impression of Pentecopterus by Patrick James Lynch, Yale University Office of Public Affairs & Communications
Patrick Lynch -- Yale University, No usage restrictions, via EurekAlert! @ https://www.eurekalert.org/multimedia/649868

"Fossils Show Big Bug Ruled the Seas 460 Million Years Ago" (2:31)
Uploaded September 2, 2015, by The Red Phoenix to YouTube ~ URL: https://www.youtube.com/watch?v=DtqAwJsf5p0

closeup of setae (bristles) covering ventral prosimal integument (= underside of anterior segment of tough outer protective layer) of Pentecopterus decorahensis
figure oriented with specimen anterior to left; scale bar = 1 millimeter
J. Lamsdell et al., "The oldest described eurypterid," BMC Evolutionary Biology, vol. 15 (2015), Figure 4: James Lamsdell, No usage restrictions, via EurekAlert! @ https://www.eurekalert.org/multimedia/649873

Decorah Crater: 470- million-year-old meteorite crater concealed beneath bedrock and, at depth of 50-p feet below Upper Iowa River's bottom, Winneshiek Shale Lagerstätte sediments, which yield extraordinarily well-preserved fossils such as Pentecopterus
Three-dimensional (3D) 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.
graphic by Adam Kiel/Northeast Iowa RC&D (Northeast Iowa Resource Conservation & Development): Department of the Interior/USGS, Public Domain, via U.S. Geological Survey @ https://www.usgs.gov/media/images/3-d-perspective-view-decorah-impact

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• Available @ http://www.msn.com/en-us/news/other/fossils-show-big-bug-ruled-the-seas-460-million-years-ago/ar-AAdNXCS?ocid=ansmsnnews11

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• Available @ https://www.iaa.uni-rostock.de/forschung/laufende-forschungsprojekte/american-antiquities-prof-mackenthun/project/artifacts/tiere-der-urwelt-trilogy/

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• Available @ http://westerndigs.org/incredibly-bizarre-giant-sea-scorpion-discovered-in-iowa-fossil/

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Lamsdell, 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. doi.org/10.1186/s12862-015-0443-9. Retrieved September 3, 2015.

• Available @ http://www.biomedcentral.com/1471-2148/15/169
• Available @ https://www.researchgate.net/publication/281521147_The_oldest_described_eurypterid_a_giant_Middle_Ordovician_Darriwilian_megalograptid_from_the_Winneshiek_Lagerstatte_of_Iowa
• Available @ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4556007/

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