| abstract
| - Altispinax (meaning "high spine") was a genus of spinosaurid dinosaur which lived during the early Cretaceous of Europe. The type species, Altispinax dunkeri (Dames, 1884 and von Huene, 1923), is known only from teeth. Other described species have since been moved to other genera, including Baryonyx. Vertebrae initially linked with the teeth are now known to be from the carnosaur Becklespinax. Thus Altispinax is now usually considered a nomen dubium. Its type species, Megalosaurus dunkeri, was originally named and described by Wilhelm Barnim Dames on 16 December 1884 during a lecture.[3] 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.[4] 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.[3] 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,[5] 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.[6] The first to actually use it was Oskar Kuhn in 1939.[7] 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.[8] 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.[9] 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.[10] 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.[6] In 1991 Olshevsky created a separate genus Valdoraptor for this species.[10] In 1932 von Huene renamed Megalosaurus parkeri Huene 1923 into Altispinax parkeri.[11] 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.[12] 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.[13] 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.[3] 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.
- Probably during the early 1850s, fossil collector Samuel Husbands Beckles discovered some nodules with dinosaur bones in a quarry near Battle, East Sussex. These he sent to palaeontologist Richard Owen, who reported them in 1856. Owen had a lithography made by Joseph Dinkel of the main specimen, a series of three back vertebrae with very tall spines, whose image was also shown in an 1884 edition of an 1855 volume of his standard work on British fossil reptiles, leading to the misunderstanding the fossils had been recovered close to 1884. Owen, who referred the specimens to Megalosaurus bucklandii, thought the vertebrae were part of the shoulder region and it has been assumed that he must have already known of the find in 1853 as he directed Benjamin Waterhouse Hawkins to put a hump on the back of his life-sized Megalosaurus sculpture in Crystal Palace Park, which again inspired other restorations from the 19th century. The fossil, now catalogued as BMNH R1828, was probably found in a layer of the Hastings Bed Group dating from the late Valanginian age. It consists of a series of three posterior dorsal vertebrae. Owen also reported the presence in the nodules of two right ribs and two additional series of two dorsal vertebral centra each. Olshevsky thought the holotype represented the eighth, ninth, and tenth dorsal vertebra; later researchers, however, have assumed them to be the tenth, eleventh and twelfth. In 1888, Richard Lydekker compared these vertebrae with material referred to Megalosaurus dunkeri, a Cretaceous species represented by a single tooth found in Germany.[6] In 1923 Friedrich von Huene created a separate genus for Megalosaurus dunkeri. He used the three vertebrae as the basis for this genus, noting that they were different from Megalosaurus, and created the name Altispinax (meaning "with high spines") based on their appearance. Many later researchers concluded that Megalosaurus dunkeri had therefore received a new genus name as Altispinax dunkeri, a combination actually used for the first time in 1939 by Oskar Kuhn. Later researchers considered Altispinax a nomen dubium because the single tooth was undiagnostic. No relationship could be proven between the tooth and the vertebrae. The vertebrae were therefore given a new name in 1988 by Gregory Paul. Paul considered them to represent a possible new species of Acrocanthosaurus, which he named Acrocanthosaurus? altispinax. The specific name was deliberately made identical to the old generic name, to emphasize that both referred to the vertebrae. As indicated by the question mark, Paul himself was uncertain about this assignment. For this reason, in 1991 a new genus, Becklespinax, was named for the vertebrae by George Olshevsky, in honour of the original discoverer, Beckles. The new combination name of the type species Acrocanthosaurus? altispinax thus became Becklespinax altispinax. The species names Altispinax altispinax and Altispinax lydekkerhueneorum are its junior objective synonyms. In 2016, a re-examination of this convoluted history of classification was published by Michael Maisch. Maisch concluded that von Huene, when he named Altispinax dunkeri, deliberately based the species on the vertebrae and not on the Megalosaurus dunkeri tooth. Because both species were based on different type specimens, later researchers were wrong to consider them the same species. Rather, according to Maisch's interpretation of the rules of the ICZN, Altispinax dunkeri (based on the tall-spined vertebrae) and Megalosaurus dunkeri (based on the tooth from Germany) are two distinct species that happen to share the same species name. Because the later names created by Paul and Olshevsky were based on the same vertebrae used to von Huene to name Altispinax dunkeri, all of those later names must be considered junior objective synonyms (different names for exactly the same fossil), and Altispinax dunkeri, having been named first, has priority as the correct name for this species.
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