South Dakota Ammonites The ammonites of South Dakota were residents of the Pierre Seaway. The Pierre Seaway expanded and contracted throught the Cretaceous Period (144 - 66.5 million years ago). The Pierre shales, which we find most of the ammonites in, were laid down during the Campion and Maastrichtian Stages (82 - 69 million years ago). This page has been set up to expedite your search for South Dakota ammonites. They will be sorted first by Genus. And finally, where enough detail is warrented, by species. |
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