Pentecopterus – A Giant Sea Scorpion from the Prehistoric Seas

Biologists Discover Giant Sea Scorpion Pentecopterus

Geologists discovered the fossils of Pentecopterus in a meteorite crater by the Upper Iowa River in northeastern Iowa.

You don’t name a sea creature after an ancient Greek warship unless it’s built like a predator.

That’s certainly true of the recently discovered Pentecopterus, a giant sea scorpion with the sleek features of a penteconter, one of the first Greek galley ships. A Yale University research team says Pentecopterus lived 467 million years ago and could grow to nearly six feet, with a long head shield, a narrow body, and large, grasping limbs for trapping prey. It is the oldest described eurypterid — a group of aquatic arthropods that are ancestors of modern spiders, lobsters, and ticks.

A detailed description of the animal appears in the September 1 online edition of the journal BMC Evolutionary Biology.

“This shows that eurypterids evolved some 10 million years earlier than we thought, and the relationship of the new animal to other eurypterids shows that they must have been very diverse during this early time of their evolution, even though they are very rare in the fossil record,” said James Lamsdell, a postdoctoral associate at Yale University and lead author of the study.

“Pentecopterus is large and predatory, and eurypterids must have been important predators in these early Palaeozoic ecosystems,” Lamsdell said.

Geologists with the Iowa Geological Survey at the University of Iowa discovered the fossil bed in a meteorite crater by the Upper Iowa River in northeastern Iowa. Fossils were then unearthed and collected by temporarily damming the river in 2010. Researchers from Yale and the University of Iowa have led the analysis.

The fossil-rich site yielded both adult and juvenile Pentecopterus specimens, giving the researchers a wealth of data about the animal’s development. In addition, the researchers said, the specimens were exceptionally well preserved.

“The Winneshiek site is an extraordinary discovery,” said Yale paleontologist Derek Briggs, co-author of the study. “The fossils are preserved in fine deposits of sediments where the sea flooded a meteorite impact crater just over 5 km in diameter.” Briggs is the G. Evelyn Hutchinson Professor of Geology and Geophysics at Yale and curator of invertebrate paleontology at the Yale Peabody Museum of Natural History.

“What’s amazing is the Winneshiek fauna comprise many new taxa, including Pentecopterus, which lived in a shallow marine environment, likely in brakish water with low salinity that was inhospitable to typical marine taxa,” said Huaibao Liu of the Iowa Geological Survey and the University of Iowa, who led the fossil dig and is a co-author of the paper. “The undisturbed, oxygen-poor bottom waters within the meteorite crater led to the fossils’ remarkable preservation. So this discovery opens a new picture of the Ordovician community that is significantly different from normal marine faunas.”

The National Science Foundation supported the research. Additional co-authors of the study were Robert M. McKay and Brian Witzke of the Iowa Geological Survey and the University of Iowa.

Publication: James C. Lamsdell, et al., “The oldest described eurypterid: a giant Middle Ordovician (Darriwilian) megalograptid from the Winneshiek Lagerstätte of Iowa,” BMC Evolutionary Biology 2015; doi:10.1186/s12862-015-0443-9

Source: Jim Shelton, Yale University

Illustration by Patrick Lynch

1 Comment on "Pentecopterus – A Giant Sea Scorpion from the Prehistoric Seas"

  1. Madanagopal.V.C. | September 2, 2015 at 12:35 am | Reply

    Giant size to mini size and from mini size to giant size of living beings are an automatic dance of evolution. Once upon a time even the horse was just a miniature sized which has grown to the present size in the struggle for existence since it wanted to run fast from its enemies. The giant sized dinosaurs when became extinct it has assumed the small size of reptiles. As long as there were plenty of plant food available they increased their size without bothering about any predators. Once the size has become small,as in reptiles, it went on small pries and even they turned carnivorous. Mammoths when they had plant food in plenty reduced their sizes to the present pachyderms in the environment of depletion of food. Scorpion of the sea also was like that since they were carnivorous and they could take food in plenty in waters. Once the survival became very difficult they became land based and grown very very small to eat insects like cockroaches.
    Struggle for existence and survival of the fittest is the motive for development of sizes of any animal , be it be tiger or cat without altering their food habits and preying upon smaller creatures. Thank You.

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