Decorah crater

The crater is estimated to be in diameter, covered by the Winneshiek Shale. There is no surface evidence of the impact, as the Winneshiek Shale is more than below the bottom of the Upper Iowa River. The impact event, equivalent to 1,000 megatons of TNT, It may be one of several Middle Ordovician meteors that fell roughly simultaneously 469 million years ago, part of a proposed Ordovician meteor event, including three confirmed impact craters: Rock Elm crater in Wisconsin, Slate Islands crater in Lake Superior, and Ames crater in Oklahoma. {{wide image|Decorah crater 2.jpg|500px||100%|center ==Pentecopterus decorahensis==

The Middle Ordovician (Darriwilian) Winneshiek Lagerstätte sediments that filled in the crater contained a wide variety of unusual fauna. Among them was a newly discovered species of eurypterid, Pentecopterus decorahensis. Pentecopterus was scorpion-like in appearance, and the largest predator known from that time, measuring nearly 6 feet in length. Its species name was derived from "Decorah." == See also ==