Altispinax is a genus of large predatory theropod dinosaur from the Early Cretaceous (Barremian) Obernkirchen Sandstein of Niedersachsen, Germany. It is only known from a single tooth. Material has also been referred to it from the Hastings Beds (Valanginian), Purbeck Beds (Early Cretaceous), and Lower Greensand (Aptian) of England, and the Weald Clay (Hauterivian-Barremian) of England and Belgium, but this material probably does not belong to Altispinax. Three back vertebrae with high spines, earlier usually associated with Altispinax and the reason for its name, have later been named as the separate genus Becklespinax.Its type species, Megalosaurus dunkeri, was originally named and described by Wilhelm Barnim Dames on 16 December 1884 during a lecture. A synopsis of the lecture was actually published in 1885, but because this was in the form of an 1884 yearbook, the latter date is usually given. However, some sources indicate 1887 as the year of publication and designate the species as a Megalosaurus dunkeri Dames vide Koken 1887, because in that year, the type specimen, a single tooth, was again described and also illustrated in a publication by Ernst Koken. The specific name honours paleontologist Wilhelm Dunker, who, many years earlier, had discovered the tooth on the Deister, in the main coal seam of Obernkirchen. This holotype had been, under the inventory number UM 84, added by him to the collection of the University of Marburg.In 1888, Richard Lydekker redescribed many fragmentary specimens from the Cretaceous of England which previously had been assigned to Megalosaurus bucklandii. Because the latter is a Jurassic species, he referred them to the Cretaceous Megalosaurus dunkeri, which thus generally became to be understood as a British Early Cretaceous theropod. In 1923, Friedrich von Huene created a separate genus for Megalosaurus dunkeri: Altispinax. The generic name is derived from Latin "altus" meaning "high" and Neolatin "spinax", as "with spines". The name was inspired by specimen BMNH R1828, a series of three dorsal vertebrae with very high spines that von Huene referred to the species. Although implicitly the new combination name of the type species Megalosaurus dunkeri was Altispinax dunkeri, this combination does not occur in the 1923 publication. The first to actually use it was Oskar Kuhn in 1939. Contrary to normal practice, von Huene in 1926 again named Altispinax based on the vertebrae, on the condition they could be shown to belong to the Megalosaurus dunkeri material. Such a second naming act is invalid, however.After 1926, Altispinax was usually seen as a British dinosaur with a high sail on its back. However, later in the twentieth century it was realised that the German type specimen, the tooth, was undiagnostic, making Altispinax a nomen dubium with no provable connection to the spines. In 1988 Gregory S. Paul created a separate species for the vertebrae series, that he assigned to Acrocanthosaurus as an Acrocanthosaurus? altispinax. As already indicated by the question mark, Paul himself considered this designation to be tentative. Therefore, in 1991 George Olshevsky named a separate genus Becklespinax for the spined vertebrae.Four other species would be named within the genus Altispinax. In 1923 von Huene renamed Megalosaurus oweni Lydekker 1889, based on the metatarsus BMNH R2559, into Altispinax oweni. In 1991 Olshevsky created a separate genus Valdoraptor for this species. In 1932 von Huene renamed Megalosaurus parkeri Huene 1923 into Altispinax parkeri. This species in 1964 was given the separate generic name Metriacanthosaurus. In 2000, Oliver Wilhelm Mischa Rauhut, assuming the 1923 naming by von Huene was invalid because the combination Altispinax dunkeri had not been mentioned, considered the 1926 naming to be valid and to pertain only to the vertebrae. The name Becklespinax would then be redundant and the name Altispinax could be maintained with the new combination name Altispinax altispinax for the vertebrae. This name is thus a junior objective synonym of Becklespinax. The same is true for Altispinax lydekkerhueneorum, a nomen nudum in 1995 used by S. Pickering for the vertebrae.The only fossil that can be reliably assigned to the Altispinax material, the original tooth, consists of a crown with a length of six centimetres and a base length of twenty-two millimetres. It is moderately recurved with serrations on its back edge running all the way to the base. Dames concluded that there were two traits in which the tooth of M. dunkeri differed from that of M. bucklandii: the lack of serrations on the front edge and the flatter cross-section. However, already Lydekker pointed out that the serrations could have been worn off, and the greater flatness could have been caused by a compression of the fossil.