Elegestolepis
The Elegestolepis is shrouded in much mystery. Scientists only know what they could glean from fossilized placoid scales. The sharks were believed to be covered in placoid scales that were hydro-dynamically shaped to keep down water resistance.
These sharks were believed to have lived in the late Silurian period, more than 420 million years ago. They are thought to be one of the earliest sharks, even predating much of the life on land.