Cretoxyrhina

Cretoxyrhina (/ˌkrˈɪtɔːksiːrhaɪnə/; meaning 'Cretaceous sharp-nose') is an extinct genus of large mackerel shark that lived about 107 to 73 million years ago during the late Albian to late Campanian of the Late Cretaceous period. The type species, C. mantelli, is more commonly referred to as the Ginsu shark, first popularized in reference to the Ginsu knife, as its theoretical feeding mechanism is often compared with the 'slicing and dicing' when one uses the knife. Cretoxyrhina is traditionally classified as the likely sole member of the family Cretoxyrhinidae but other taxonomic placements have been proposed, such as within the Alopiidae and Lamnidae. Measuring up to 8 meters (26 ft) in length and weighing up to 3,400 kilograms (3.3 long tons; 3.7 short tons), Cretoxyrhina was one of the largest sharks of its time. Having a similar appearance and build to the modern great white shark, it was an apex predator in its ecosystem and preyed on a large variety of marine animals including mosasaurs and plesiosaurs, sharks and other large fish, pterosaurs, and occasionally dinosaurs. Its teeth, up to 8 centimeters (3 in) in height, were razor-like and had thick enamel built for stabbing and slicing prey. Cretoxyrhina was also among the fastest-swimming sharks, being capable of pursuing prey with burst speeds of up to 70 kilometers per hour (43 mph). It has been speculated that Cretoxyrhina hunted by lunging at its prey at high speeds to inflict powerful blows, similar to the great white shark today, and relied on strong eyesight to do so. Since the late 19th century, several fossils of exceptionally well-preserved skeletons of Cretoxyrhina have been discovered in Kansas. Studies have successfully calculated its life history using vertebrae from some of the skeletons. Cretoxyrhina grew rapidly during early ages and reached sexual maturity at around four to five years of age. Its lifespan has been calculated to extend to nearly forty years. Anatomical analysis of the Cretoxyrhina skeletons revealed that the shark possessed facial and optical features most similar to that in thresher sharks and crocodile sharks and had a hydrodynamic build that suggested the use of regional endothermy. As an apex predator, Cretoxyrhina played a critical role in the marine ecosystems it inhabited. It was a cosmopolitan genus and its fossils have been found worldwide, although most frequently in the Western Interior Seaway area of North America. It preferred mainly subtropical to temperate pelagic environments but was known in waters as cold as 5 °C (41 °F). Cretoxyrhina saw its peak in size by the Coniacian, but subsequently experienced a continuous decline until its extinction during the Campanian. One factor in this demise may have been increasing pressure from competition with predators that arose around the same time, most notably the giant mosasaur Tylosaurus. Other possible factors include the gradual disappearance of the Western Interior Seaway. Cretoxyrhina was first described by the English paleontologist Gideon Mantell from eight C. mantelli teeth he collected from the Southerham Grey Pit near Lewes, East Sussex. In his 1822 book The fossils of the South Downs, he identified them as teeth pertaining to two species of locally-known modern sharks. Mantell identified the smaller teeth as from the common smooth-hound and the larger teeth as from the smooth hammerhead, expressing some hesitation to the latter. In 1843, Swiss naturalist Louis Agassiz published the third volume of his book Recherches sur les poissons fossiles, where he reexamined Mantell's eight teeth. Using them and another tooth from the collection of the Strasbourg Museum (whose exact location was unspecified but also came from England), he concluded that the fossils actually pertained to a single species of extinct shark that held strong dental similarities with the three species then classified in the now-invalid genus Oxyrhina, O. hastalis, O. xiphodon, and O. desorii. Agassiz placed the species in the genus Oxyrhina but noted that the much thicker root of its teeth made enough of a difference to be a distinct species and scientifically classified the shark under the taxon Oxyrhina mantellii and named in honor of Mantell. During the late 19th century, paleontologists described numerous species that are now synonymized as Cretoxyrhina mantelli. According to some, there may have been as much as almost 30 different synonyms of O. mantelli at the time. Most of these species were derived from teeth that represented variations of C. mantelli but deviated from the exact characteristics of the syntypes. For example, in 1870, French paleontologist Henri Sauvage identified teeth from France that greatly resembled the O. mantelli syntypes from England. The teeth also included lateral cusplets (small enameled cusps that appear at the base of the tooth's main crown), which are not present in the syntypes, which led him to describe the teeth under the species name Otodus oxyrinoides based on the lateral cusplets. In 1873, American paleontologist Joseph Leidy identified teeth from Kansas and Mississippi and described them under the species name Oxyrhina extenta. These teeth were broader and more robust than the O. mantelli syntypes from England. This all changed with the discoveries of some exceptionally well-preserved skeletons of the shark in the Niobrara Formation in West Kansas. Charles H. Sternberg discovered the first skeleton in 1890, which he described in a 1907 paper: Charles R. Eastman published his analysis of the skeleton in 1894. In the paper, he reconstructed the dentition based on the skeleton's disarticulated tooth set. Using the reconstruction, Eastman identified the many extinct shark species and found that their fossils are actually different tooth types of O. mantelli, which he all moved into the species. This skeleton, which Sternberg had sold to the Ludwig Maximilian University of Munich, was destroyed in 1944 by allied bombing during World War II. In 1891, Sternberg's son George F. Sternberg discovered a second O. mantelli skeleton now housed in the University of Kansas Museum of Natural History as KUVP 247. This skeleton was reported to measure 6.1 meters (20 ft) in length and consists of a partial vertebral column with skeletal remains of a Xiphactinus as stomach contents and partial jaws with about 150 teeth visible. This skeleton was considered to be one of the greatest scientific discoveries of that year due to the unexpected preservation of cartilage. George F. Sternberg would later discover more O. mantelli skeletons throughout his career. His most notable finds were FHSM VP-323 and FHSM VP-2187, found in 1950 and 1965 respectively. The former is a partial skeleton consisting of a well-preserved set of jaws, a pair of five gills, and some vertebra while the latter is a near-complete skeleton with an almost complete vertebral column and an exceptionally preserved skull holding much of the cranial elements, jaws, teeth, a set of scales, and fragments of pectoral girdles and fins in their natural positions. Both skeletons are currently housed in the Sternberg Museum of Natural History. In 1968, a collector named Tim Basgall discovered another notable skeleton that, similar to FHSM VP-2187, also consisted of a near-complete vertebral column and a partially preserved skull. This fossil is housed in the University of Kansas Museum of Natural History as KUVP 69102.