Cretoxyrhina

Cretoxyrhina mantelli was one of the largest sharks and a formidable predator in the Late Cretaceous seas. Nicknamed the Ginsu shark, Cretoxyrhina ripped apart prey with a mouth full of razor-sharp, bone-shearing teeth. Evidence suggests Cretoxyrhina fed on mosasaurs, plesiosaurs, and even the giant bony fish Xiphactinus, a fierce predator itself. Despite its fearsome size and armament, C. mantelli did not long survive, becoming extinct by about 90 million years ago.

Fossils
Sharks are made of cartilage, which does not fossilize well. Much of what is known about them comes from their abundant—and harder—teeth. Cretoxyrhina mantelli teeth often grew more than two inches (five centimeters) long. Bite marks and teeth embedded in the bones of its prey suggest Cretoxyrhina chomped with brutal force.

Most Cretaceous sharks are known primarily from isolated fossilized teeth. In contrast, several nearly complete skeletons of C. mantelli have been discovered. These astonishing fossil finds include disarticulated clusters of vertebrae with associated upper and lower tooth sets lying in clear arcs, giving a vivid impression of Cretoxyrhina's body length and mouth width. Remarkably, paleontologists have also discovered at least two mineralized impressions of C. mantelli skin, with tooth-like dermal denticles still anchored in place. From these and other, less spectacular finds, we know that Cretoxyrhina mantelli lived globally in oceanic and coastal areas, including the Western Interior Sea (sometimes known by more evocative name, Sundance Sea) which had flooded inland North America during the Mesozoic.

Estimates from a few calcified remains of cartilaginous Ginsu sharks suggest they grew upwards of 24 feet (7 meters) long, similar in size to modern great white sharks. Though fierce and feared, Cretoxyrhina was preyed upon by the giant mosasaur Tylosaurus, and C. mantelli remains were scavenged by the smaller shark of its time, Squalicorax. Fossil tooth marks suggest Cretoxyrhina and Squalicorax sharks went after the same food, either hunting together or stealing from each other.

Teeth
Hundreds of Cretoxyrhina mantelli teeth have been collected from late Cretaceous deposits in the western part of that state, indicating that this species was once quite abundant there. Each of these teeth had a smooth-edged blade and resembled those of a mako, but were much broader and more massive with an unusually thick enameloid coating. Such teeth clearly enabled it to feed on large, active, and well-armed prey.

Recent Events
A recent paper by paleontologist Kenshu Shimada reviewed the paleoecology of Cretoxyrhina mantelli from late Cretaceous deposits in Kansas. According to Shimada, associated fossil remains with evidence of digestive damage suggest that probable fish prey of C. mantelli included the massively jawed, 14-foot (4.25-metre) long Xiphactinus, which resembled a dagger-toothed tarpon and was a powerful predator in its own right. Based on a few tooth-scarred, associated mosasaur vertebrae, Shimada suggests that C. mantelli also tackled these 10- to 40-foot (3- to 12- metre) long marine reptiles of the late Cretaceous.