| Altispinax | |
|---|---|
 | |
| Holotype (NHMUK R1828) illustrated c. 1850s | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Clade: | †Carnosauria |
| Genus: | †Altispinax von Huene, 1923 |
| Species: | †A. dunkeri |
| Binomial name | |
| †Altispinax dunkeri von Huene, 1923 | |
| Synonyms | |
| |
Altispinax (/ˌæltɪˈspaɪnæks/; "with high spines") is agenus of large predatorytheropoddinosaur from theEarly Cretaceous period (Valanginian, 140 to 133 million years ago) of what is now theWadhurst Clay Formation ofEast Sussex,England.
Probably during the early 1850s,fossil collectorSamuel Husbands Beckles discovered somenodules with dinosaur bones in a quarry nearBattle, East Sussex. These he sent to palaeontologistRichard Owen, who reported them in 1856.[1] Owen had alithograph made byJoseph Dinkel of the main specimen, a series of three backvertebrae 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,[2] leading to the misunderstanding the fossils had been recovered close to 1884. Owen, who referred the specimens toMegalosaurus 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 directedBenjamin Waterhouse Hawkins to put a hump on the back of his life-sizedMegalosaurus sculpture inCrystal Palace Park, which again inspired other restorations from the 19th century.[3][4]
The fossil, now catalogued asNHMUK PV R 1828, was probably found in a layer of theHastings Bed Group dating from the lateValanginian 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.[1] Olshevsky thought the holotype represented the eighth, ninth, and tenth dorsal vertebrae; later researchers, however, have assumed them to be the tenth, eleventh and twelfth.[5]
In 1888,Richard Lydekker compared these vertebrae with material referred toMegalosaurus dunkeri, a Cretaceous species represented by a single tooth found in Germany.[6] In 1923Friedrich von Huene created a separate genus forMegalosaurus dunkeri. He used the three vertebrae as the basis for this genus, noting that they were different fromMegalosaurus, and created the nameAltispinax (meaning "with high spines") based on their appearance. Many later researchers concluded thatMegalosaurus dunkeri had therefore received a new genus name asAltispinax dunkeri, a combination actually used for the first time in 1939 byOskar Kuhn.[7]
Later researchers consideredAltispinax anomen 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 byGregory Paul. Paul considered them to represent a possible new species ofAcrocanthosaurus, which he namedAcrocanthosaurus? altispinax. Thespecific name was deliberately made identical to the old generic name, to emphasize that both referred to the vertebrae.[8] 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 thetype speciesAcrocanthosaurus? altispinax thus becameBecklespinax altispinax.[9] The species namesAltispinax altispinax[10][11] andAltispinax lydekkerhueneorum[12] are itsjunior 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 namedAltispinax dunkeri, deliberately based the species on the vertebrae and not on theMegalosaurus 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 theICZN,Altispinax dunkeri (based on the tall-spined vertebrae) andMegalosaurus 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 by von Huene to nameAltispinax dunkeri, all of those later names must be considered junior objective synonyms (different names for exactly the same fossil), andAltispinax dunkeri, having been named first, has priority as the correct name for this species.[13]
Four other species would be named within the genusAltispinax. In 1923 von Huene renamedMegalosaurus oweni Lydekker 1889, based on themetatarsus BMNH R2559, intoAltispinax oweni.[14] In 1991 Olshevsky created a separate genusValdoraptor for this species.[9] In 1932 von Huene renamedMegalosaurus parkeri Huene 1923 intoAltispinax parkeri.[15] This species in 1964 was given the separate generic nameMetriacanthosaurus.
Paul in 1988 tentatively estimated thatAltispinax weighed 1 tonne (1.1 short tons) and was shorter than the type specimen ofAcrocanthosaurus atokensis which measures about 8 meters (26 ft) long.[8]
The threeA. dunkeri back vertebrae from Sussex have about thirty-five centimetres highneural spines orprocessus spinosi, about as relatively tall as those ofIchthyovenator.[16] These show irregular rugosities on the upper third part. According toRalph Molnar the two spines closest to the skull are ankylosed or fused. The single closest spine is only about two-thirds the height of the others and looks as it has broken off, while the spine behind partly overgrows the gap. This Molnar explained as a result of injury to a back frill, the wound later closing from behind.[5] In 2003,Darren Naish gave a different interpretation, suggesting the gap was natural. He denied that the front two vertebrae were ankylosed but observed that the spines of eleventh and twelfth vertebrae were joined at the top. The spines are also transversely expanded above, with a width of about fifty-five millimetres. Naish also pointed out that Owen had noted the large depressions on theneural arch sides and had explained them as a result ofpneumatisation, the first time this phenomenon would explicitly have been observed with a dinosaur.[17][18] In 2006 however, it was reported that in 1837Christian Erich Hermann von Meyer already had commented on this phenomenon with theSaurischia in general.[19] The discovery of a back crest incorporating only two high vertebrae inConcavenator, in 2010 provided corroboration that the short anteriorAltispinax spine may be complete.[20]
Olshevsky originally assignedAltispinax to theEustreptospondylidae. In 2003 Naish considered it a member of theAllosauroidea.[17] Most researchers give a less precise placement asTetanuraeincertae sedis.[21][22]
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