All About Sharks
The Strange and Terrifying World of Prehistoric Sharks
Since first appearing at least 420 million years ago, sharks have undergone many strange and sometimes terrifying changes to evolve into the sharks we know today.
INTERACTIVE TIMELINE OF SHARK EVOLUTION
Sharks are among Earth’s oldest lifeforms, having appeared at least 420 million years ago – nearly 200 million years before the first dinosaurs. Trace the evolution of sharks. Tap or click on hotspots for more information. EXPLORE THE TIMELINE
Spotlight on Science
How Do Experts Know About Prehistoric Sharks?
Paleontologists study fossilized bones to learn how creatures evolved. But sharks don’t have bones; they have cartilage, which dissolves quickly in ocean water. Luckily, after some sharks died, their bodies lay on rocks, leaving a fossilized impression on the rocks. Studying these gives good clues about shark evolution.
So, how exactly did sharks evolve over time? Some were born with features that made them better able to survive. A shark with a useful feature would pass along that feature to its offspring. Over millions of years, this happened from generation to generation. Sharks with superior features reproduced rapidly and sharks without those features died off because they couldn’t compete successfully for food and mates.
One example of this can be found in the special way shark jaws work. Scientists believe that the first sharks with jaws that were not fused to their heads appeared about 200 million years ago. This gave them the ability to thrust their jaws forward and catch prey efficiently. Today, many sharks have this feature.
How Did Prehistoric Sharks Escape Mass Extinction?
About 250 million years ago, life on Earth was flourishing … and then suddenly, what came to be known as the “Great Dying” occurred, wiping out roughly nine in 10 marine species and seven in 10 land species. Plants, insects, microbes, proto-mammals, fish -- nothing was spared. While the cause is of the event is still unknown (although scientists think it was likely due to volcanic activity or climate change), what’s much more certain is that life on Earth nearly came to an END.
So how did sharks overcome the odds and survive such a mass extinction?
They dove deeper.
In 2013, a paleontological dig site in southern France yielded fossilized teeth of a tiny shark relative, indicating that the fish escaped catastrophic events by swimming to deeper oceans.
The sharks discovered in the limestone bed were likely only about 8 inches (20 centimeters) long, and their teeth were only about a millimeter across. While small, however, the sharks were true predators, preying on the ancestors of today’s squids and small fish. But most importantly, they were just flexible enough in their diet to survive in the deep ocean while the events causing the mass extinction of their fellow Earthlings played out above them.
Sharks: the original practitioners of “duck and cover.”