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.
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.
Early fossil discoveries
In the 17th century, Nicholas Steno shook the world of science, noting the similarity between shark teeth and the rocks commonly known as “tongue stones.” This was our first understanding that fossils were a record of past life.
Two centuries later, Mary Ann Mantell picked up a tooth, which her husband Gideon thought to be of a large iguana, but it turned out to be the tooth of a dinosaur, Iguanodon. This discovery sent the powerful message that many fossils represented forms of life that are no longer with us today.
Additional clues from fossils
Today we may take fossils for granted, but we continue to learn from them. Each new fossil contains additional clues that increase our understanding of life’s history and help us to answer questions about their evolutionary story. Examples include: