Megalodon shark and great white
Megalodon shark (Carcharodon megalodon), computer artwork. A great white shark (Carcharodon carcharias) is shown below it at the same scale. This enormous shark lived between around 20 and 1.2 million years ago, and is known from fossils. It was related to the modern great white shark, and is thought to have fed on whales, as this is the only source of food that could have provided it with enough meat. Megalodon was thought to attain lengths exceeding 20 metres, and possibly significantly larger. It is thought that it died out after the seas cooled, allowing warm-blooded whales to escape the sharks for much of the year by swimming to waters too cold for them to survive in.
© CHRISTIAN DARKIN/SCIENCE PHOTO LIBRARY
Whale shark and pilot fish
Whale shark (Rhincodon typus) about to eat a pilot fish (Naucrates ductor). The whale shark is the largest fish in the world, growing up to 18 metres in length. This harmless, solitary animal is found in tropical and warm waters throughout the world, except the Mediterranean. It is a filter feeder, straining plankton and small organisms from the water. It generates its own suction rather than relying on its forward motion and schooling fish may be eaten at times. The pilot fish is a scavenger well know for its habit of accompanying ships and large fish, especially sharks, in warm waters. Photographed in the Red Sea, Egypt.
© Alexis Rosenfeld/Science Photo Library
Steno's shark tooth fossil
Great white shark jaw with fossil shark teeth. Copperplate after Steno 1667. Steno produced a book "Head of a shark dissected" from his dissection of a great white shark caught in the Mediterranean and brought to him in Florence. In it he notes that the 'Glossopetrae' or 'tongue stones' of Pliny are in fact sharks teeth. This was also a conclusion alluded to a century before by Conrad Gesner (see other image in this collection). And Gesner may himself have been led to that conclusion if he read Guillaume Rondelet's 1554 comparison of shark's teeth and tongue stones in his compendium of Mediterranean fishes. Steno however was the first to come up with coherent theories about how such teeth had turned to stone and how they could be found in the ground far from the sea.
© PAUL D STEWART/SCIENCE PHOTO LIBRARY