This image is of Ptychodus whipple fossil ancestral stingray teeth on display at Mace Brown Museum of Natural History (August 2017). They date to the Campanian Age (about 80 million years ago), Late Cretaceous Period. The fossils were found in the Eagle Ford Shale Grayson County Texas USA.
Learn more at their blog: http://blogs.cofc.edu/macebrownmuseum/