Cretoxyrhina, informally known as the ginsu shark, is a cretoxyrhinid mackerel shark from the Early-Late Cretaceous of the entire world. It was officially named in 1843 by Louis Agassiz. It was one of the biggest macropredatory (eating animals its size or larger) sharks to exist during the Cretaceous, and held the position of an aquatic top predator, even after larger marine reptiles came into the scene.
For the most part, Cretoxyrhina resembled a typical mackerel shark, with a torpedo-shaped body, triangular pectoral (arm) and dorsal (back) fins, a crescent-shaped caudal (tail) fin, a mid-sized head with a conical nose and large jaws, and 5 gills located near the head on each side of its body. However, its head was much like that of a thresher shark, as it had proportionally large eyes relative to its head, and its nose was rounded rather than pointy. Its body would have been covered in scaly skin.
Cretoxyrhina was a predator, preying on fish, cephalopods, turtles, diving birds, small plesiosaurs, pterosaurs, and small mosasaurs. Its teeth were sharp, bore smooth serrations, and built on thick enamel (mineralized base that protects the tooth), allowing it to bite through any organic substance.
Cretoxyrhina was a formidable carnivore, and was capable of preying on many large marine animals that existed with it; many small mosasaur vertebrae with tooth marks show that they were a common staple of its diet (whether they were dead and alive), and fossil remains with noticeable bite damage showed that many of the fish it ate included the large, predatory Xiphactinus. Its teeth were smoothly serrated like those of a mako, but were broader, more massive, and built upon thicker enamel, allowing it to feed on large, fast-swimming, and well-armed prey; when feeding, Cretoxyrhina would have sliced its victim into bite-sized pieces, a behavior that earned it the common name of "Ginsu shark". However, despite its reputation as a fearsome predator, Cretoxyrhina is known to have scavenged from time to time (as all predators do), and bite marks on the arm of an ankylosaurian dinosaur showed that it would feed on bloated dinosaur carcasses that were washed out to sea before sinking. In general, Cretoxyrhina was a prominent predator ecologically similar to the extant great white shark, mainly feeding on bony fish, but occasionally going after vertebrate prey such as diving birds and small mosasaurs as well as feeding on carrion.
In popular culture
Cretoxyrhina was featured in the 2007 documentary Sea Monsters: A Prehistoric Adventure, where it kills the mother of the protagonist Dolichorhynchops. It appeared again in another documentary, Monsters Resurrected, where it was shown as competing with Tylosaurus for the role of apex predator in the Cretaceous seas.