When sharks ate dinosaurs

In ancient times, around 86 million years ago, the remains of a hadrosaur were washed out to sea. towering carcass to float in warm waters where hungry sharks could tear it apart. The details of this feast are told by the fossils.

An amateur fossil hunter, Keith Ewell, discovered in 2005 in the Smoky Hill Chalk geological formation in western Kansas, a series of nine bones from the tail of a dinosaur. The prehistoric site where these fossils were unearthed is surprising. During the Cretaceous, when layers of sediment from the Smoky Hill Chalk were accumulating, Kansas was partially submerged by the Western Interior Seaway. Dinosaurs did not live in this marine environment, but their remains were sometimes transported by local floods and other aquatic phenomena to the jaws of marine carnivores. If the plesiosaur, armed with its four swimming paddles, and the mosasaur, with the air of a Komodo dragon, shared the crown of reptilian predators, prehistoric sharks also pulled out of the game, as evidenced by the traces of their distinctive teeth. on the tail fossils found by Ewell.

Michael Everhart, a paleontologist at the Sternberg Museum of Natural History, described these bones in collaboration with Ewell in a study published in 2006 in the journal Transactions of the Kansas Academy of Science. This case of a dinosaur being transported at sea is not only an extremely rare event, only six cases had been recorded at Smoky Hill Chalk, but also an exceptional discovery since at least four of the vertebrae of the hadrosaurus bear teeth marks solely attributable to a scavenger shark.

It remains to be seen which shark it is. An A-shaped serrated tooth belonging to a representative of the genus Squalicorax was discovered just below the bones. However, this proximity does not necessarily mean that this tooth belonged to the shark that devoured the dinosaur’s carcass. Association does not always imply interaction. In reality, according to Everhart and Ewell, the teeth marks do not appear to have been caused by a jagged-toothed shark. It is more likely that the dinosaur was devoured by Cretoxyrhina, a genus of massive shark about six meters long, in particular because fragments of teeth of this shark were found implanted in bones showing traces of similar bites. At least one Cretoxyrhina must have bitten into the flesh of the hadrosaur.

Although exceptional, Ewell’s discovery is not an isolated case. According to Everhart, all but two of the incomplete dinosaur fossils found at Smoky Hill Chalk showed bite marks. For example, in the case of Niobrarasaurus, mostly covered with solid scales, the teeth marks indicate that the lower part of one of its forelimbs had been torn off by a Cretoxyrhina scavenger.

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