Many of the most famous dinosaurs roamed the Earth during the Cretaceous Period, some 100 million years ago. But it might be time for T. rex to move over as the most lethal giant of the Cretaceous. Scientists are discovering that the oceans of this period were teeming with sizable sharks.
In fact, sharks have a long and little known prehistoric history. The earliest shark yet discovered lived during the Ordovician Period about 420 million years ago. However, since sharks have softer cartilage instead of bone, they are often missing from the fossil record. Often the only remaining evidence of ancient sharks are their easily-fossilized hard teeth. For that reason, the history of sharks has long presented a mystery to scientists.
A recent discovery, however, casts new light on the mystery. Guillaume Guinot of the Natural History Museum in Switzerland, Charlie Underwood of Birkbeck College in London, Henri Cappetta of the University of Montpellier, and David Ward of The Natural History Museum in London have discovered the remains of no less than 96 different species of sharks in northern France and the UK. Their paper, published in the Journal of Systematic Palaeontology, details their discovery, which includes 18 species and four genera that have never been seen before, indicating that the oceans of the Cretaceous were packed with predators.
Sharks living at this time would have had to compete for food with aquatic dinosaurs and the super-sized reptiles of the period. It is even possible that some of the larger dinosaurs and pterosaurs feasted at least in part upon the smaller sharks.
It is more difficult to tell whether sharks ate dinosaurs. The foot bones of a hadrosaur, a type of duck-billed dinosaur, have been found with a shark tooth embedded in them, that of the nearly 17-foot-long Squalicorax, but it is impossible to tell if the shark attacked the living dinosaur or was just munching on carrion.
Although few of the Cretaceous sharks have close living relatives today, Guinot reports that ancient sharks probably looked much like modern sharks. Sharks have a body design so efficient that it has changed very little in the last 140 million years.
Source: Guinot, G., Underwood, C. J., Cappetta, H., & Ward, D. J. (2013). Sharks (Elasmobranchii: Euselachii) from the Late Cretaceous of France and the UK. Journal of Systematic Palaeontology, 1-83.
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