| Pelorosaurus | |
|---|---|
 | |
| Holotype humerus | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | †Sauropodomorpha |
| Clade: | †Sauropoda |
| Clade: | †Macronaria |
| Family: | †Brachiosauridae |
| Genus: | †Pelorosaurus Mantell, 1850 |
| Species: | †P. brevis |
| Binomial name | |
| †Pelorosaurus brevis (Owen, 1842) | |
| Synonyms | |
| |
Pelorosaurus (/pəˌlɒroʊˈsɔːrəs/pə-LORR-oh-SOR-əs; meaning "monstrous lizard") is a genus oftitanosauriformsauropoddinosaur. Remains referred toPelorosaurus date from the EarlyCretaceous period, about 140-125 million years ago, and have been found inEngland andPortugal.[citation needed]Thomas Holtz estimated its length at 24 meters (79 feet).[1]
The namePelorosaurus was one of the first to be given to anysauropod. Many species have been assigned to the genus historically, but most are currently considered to belong to other genera. Problematically, the first named species ofPelorosaurus,P. conybeari, is ajunior synonym ofCetiosaurus brevis.
Pelorosaurus was one of the firstsauropods to be identified as a dinosaur, although it was not the first to be discovered.Richard Owen had discoveredCetiosaurus in 1841 but had incorrectly identified it as a gigantic sea-going crocodile-like reptile.[2] Mantell identifiedPelorosaurus as a dinosaur, living on land.
The taxonomic history ofPelorosaurus andCetiosaurus, as noted by reviewers includingMichael P. Taylor andDarren Naish, is highly confusing. In 1842, Richard Owen named several species ofCetiosaurus. Among them wasCetiosaurus brevis, based on several specimens from the early Cretaceous Period. Some of these, four caudal vertebrae, NHMUK PV OR 2544–2547, and three chevrons, NHMUK PV OR 2548–2550, found around 1825 by John Kingdon nearCuckfield in theTunbridge Wells Sand Formation of theHastings Beds, belonged to sauropods. Others however, including NHMUK PV OR 10390, found nearSandown Bay on theIsle of Wight, and NHMUK PV OR 2133 and OR 2115, found near Hastings, actually belonged to someiguanodont. Noticing Owen's mistake in assigning iguanodont bones toCetiosaurus, comparative anatomistAlexander Melville renamed the sauropod bonesCetiosaurus conybeari in 1849.[3][4]
In 1850,Gideon Mantell decided thatC. conybeari was so different fromCetiosaurus that it needed a new genus, so he reclassified it under the new namePelorosaurus conybeari. Mantell had originally, in November 1849, intended to use the name "Colossosaurus", but upon discovering thatkolossos wasGreek for "statue" and not "giant", he changed his mind. The generic name is derived from the Greekpelor, "monster". He also emended thespecific name (honouringWilliam Conybeare) toconybearei, but under the present rules of theICZN, the originalconybeari, today written without a capital, has priority. Mantell not only used the sauropod material ofC. brevis as the type ofPelorosaurus conybeari but also a largehumerus found by miller Peter Fuller at the same site, NHMUK PV OR 28626, which he assumed to have been of the same individual, being discovered only a few metres away from the vertebrae. Mantell acquired the bone for £8. The humerus, clearly shaped to vertically support the weight of the body and presumed to possess amedullary cavity, showed thatPelorosaurus was a land animal. This was a main motive in naming a separate genus; shortly afterwards, however, by studying the sacral vertebrae ofCetiosaurus Mantell established that it too lived on land.[5]
Owen was highly piqued by Melville's and Mantell's attempts to "suppress" hisCetiosaurus brevis. By a publication in 1853 he tried to set matters straight, as he saw it, while avoiding having to openly admit his original mistake. First he suggested that Melville's main motivation for the name change was the presumed inaccuracy of the epithetbrevis, "short", because the total length of the animal could not be deduced from such limited remains. Owen pointed out that anyone being acquainted with taxonomy would have understood that "short" referred to the vertebrae themselves, not to the animal as a whole. On a subsequent page, apparently separate from this issue, Owen in covert terms implied that his 1842 publication was not descriptive enough, thus merely having resulted in anomen nudum, to which he now assigned the sauropod material, makingCetiosaurus brevis a valid name. This still left the problem of it having been named a new genus by Mantell. Owen resolved it by simply presenting the humerus as the soleholotype ofPelorosaurus conybeari.[6][failed verification] Remarkably, in 1859 he repeated his mistake by again referring iguanodontid vertebrae, specimens NHMUK PV OR 1010 and OR 28635, toC. brevis.[7] The last of these he had in 1853 proposed to belong toPelorosaurus together with a number of other iguanodontid vertebrae because Mantell had once labelled them as such in his collection; Owen suggested it had been by a mere mistake that the namePelorosaurus had been connected with theC. brevis material instead of with these finds.[6]
Owen's interpretation was commonly accepted until well into the twentieth century. By 1970 however, bothJohn Ostrom andRodney Steel understood that Owen's claim thatC. brevis in 1842 was still anomen nudum should be rejected as a transparent attempt to change the type specimen, inadmissible by present standards.[failed verification] By those same standards though, Melville's name change was also incorrect: as the nameCetiosaurus brevis was still "available" he should simply have made the sauropod bones thelectotype, removing the iguanodontid remains from thesyntype series. The sauropod bones, not the iguanodont bones, would then have retained the nameC. brevis. Therefore,Cetiosaurus conybeari is ajunior objective synonym ofC. brevis, that is,C. brevis is not only an older name, but one based on exactly the same fossils as the younger, invalid name.[4]
After 1850, more specimens continued to be assigned to bothPelorosaurus andCetiosaurus, and both were studied and reported on extensively in the scientific literature.[4] Slowly a tendency developed to subsume fragmentary sauropod material from the Jurassic of England under the designationCetiosaurus, while assigning incomplete European Cretaceous sauropod finds toPelorosaurus.Pelorosaurus thus came to be a typicalwastebasket taxon for any European sauropod of this period. However, in recent years much work has been done to rectify the confusion.
The validity ofPelorosaurus is problematic.P. conybeari was based on a separately discovered humerus and vertebrae. However, these specimens might not belong to the same animal.P. conybeari is also ajunior synonym of the older nameCetiosaurus brevis. In 2007, Michael P. Taylor and Darren Naish stated their intention to petition theInternational Commission on Zoological Nomenclature (ICZN) in order to designate the more widely used nameP. conybeari the type species ofPelorosaurus and officially abandon the nameC. brevis.[8] However, the issue of thePelorosaurus type species did not end up as part of their petition when it was officially filed and accepted.[9]
Many species have later been assigned toPelorosaurus, most of which today are considered different dinosaurs. One notable species,P. becklesii, was known from a humerus, radius and ulna, as well as skin impressions. This specimen has since been made the new genusHaestasaurus.
Mantell was the first to suggest a relationship betweenPelorosaurus and dinosaurs. In 1852Friedrich August Quenstedt formally listed it in theDinosauria.[10] Predictably, Owen at first rejected this classification, still in 1859 considering it a member of theCrocodilia.
In 1882Henri-Émile Sauvage first stated it belonged to theSauropoda. That group being still very incompletely known however, it proved difficult to determine its more precise affinities, with theAtlantosauridae,Cardiodontidae,Cetiosauridae andMorosauridae being suggested until in 1927 von Huene understood the possible link withBrachiosaurus, placingPelorosaurus in theBrachiosauridae, a placement followed by subsequent authors until the early 21st century. The humerus, 137 centimeters long and very elongated, strongly suggests a typical brachiosaurid trait was present: the possession of relatively long front limbs. The uncertainties about whether the qualities of the vertebrae or the humerus should be analysed, both specimens not necessarily belonging to the sametaxon, prevents any firm conclusion to be reached, however. In recent years, the material was commonly placed in a more generalTitanosauriformes.
