The fossil record provides snapshots of the past that, when assembled, illustrate a panorama of evolutionary change over the past four billion years. The picture may be smudged in places and may have bits missing, but fossil evidence clearly shows that life is old and has changed over time
Nicholas Steno's anatomical drawing of an extant shark (left) and a fossil shark tooth (right). Steno made the leap and declared that the fossil teeth indeed came from the mouths of once-living sharks.
