Scientists have discovered what they say is the oldest described eurypterid—a giant person-sized sea scorpion that lived 467 million years ago.

Eurypterids are a group of aquatic arthropods that are ancestors of modern spiders, lobsters, and ticks.

Pentecopterus, so named because of its sleek features that resembled a penteconter, one of the first Greek gallery ships, had a long head shield, a narrow body, and large, grasping limbs for trapping prey.

Pentecopterus illustration

“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,” says 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.”

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.

Remarkable preservation

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

“The Winneshiek site is an extraordinary discovery,” says Derek Briggs, professor of geology and geophysics at Yale and coauthor of the study published in the journal BMC Evolutionary Biology.

“What’s amazing is the Winneshiek fauna comprise many new taxa, including Pentecopterus, which lived in a shallow marine environment, likely in brackish water with low salinity that was inhospitable to typical marine taxa,” says Huaibao Liu of the Iowa Geological Survey and the University of Iowa, who led the fossil dig and is a coauthor 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.


This text is published here under a Creative Commons License.
Author: Jim Shelton-Yale University
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