A rostral denticle of Ischyrhiza mia, a species belonging to an extinct group of sawfishes that lived in North American waters during the late Cretaceous period, around 100 to 65 million years ago.

The curved bottom of the "foot" faces outward, while a cylindrical column at the base anchors the denticle to the shark's body. The outward shape of denticles was long believed to reduce drag ...