Skull of a late Permian synapsid or therapsid from the southwestern shore of Lake Michigan. A found piece, it’s been preserved in sandstone and sandy chert. Looks like a late dimetrodon whose skull was bashed, then worn from millions of years of erosion in one place or another. This rock and smaller similar rocks are evidence that Permian fossils lie at the bottom of Lake Michigan. There are millions of these relics, mostly tiny skulls preserved at chert. Walking along the beach with these fossils underfoot for a ¼ mile is like walking through the Permian Extinction.
Lake Michigan's Left Coast 