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. Taxonomy Research history 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