Earliest fossil evidence for sharks

Fossil traces of what may have been sharks have been found in Colorado that date back as far as the late Ordovician Period, 455 million years ago. The earliest widely accepted evidence of shark existence, however, dates back to the early Silurian Period, 420 million years ago, and consists of various isolated fossil scales, each measuring less than 1 mm long, found in deposits in Siberia. These tiny scales belonged to an ancient shark known as Elegestolepis, whose physical appearance is currently unknown.