Pelorosaurus was one of the first
sauropods to be identified as a dinosaur, although it was not the first to be discovered.
Richard Owen had discovered
Cetiosaurus in 1841 but had incorrectly identified it as a gigantic sea-going crocodile-like reptile. Mantell identified
Pelorosaurus as a dinosaur, living on land. The taxonomic history of
Pelorosaurus and
Cetiosaurus, as noted by reviewers including
Michael P. Taylor and
Darren Naish, is highly confusing. In 1842, Richard Owen named several species of
Cetiosaurus. Among them was
Cetiosaurus 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 near
Cuckfield in the
Tunbridge Wells Sand Formation of the
Hastings Beds, belonged to sauropods. Others however, including NHMUK PV OR 10390, found near
Sandown Bay on the
Isle of Wight, and NHMUK PV OR 2133 and OR 2115, found near Hastings, actually belonged to some
iguanodont. Noticing Owen's mistake in assigning iguanodont bones to
Cetiosaurus, comparative anatomist
Alexander Melville renamed the sauropod bones
Cetiosaurus conybeari in 1849. In 1850,
Gideon Mantell decided that
C. conybeari was so different from
Cetiosaurus that it needed a new genus, so he reclassified it under the new name
Pelorosaurus conybeari. Mantell had originally, in November 1849, intended to use the name "Colossosaurus", but upon discovering that
kolossos was
Greek for "statue" and not "giant", he changed his mind. The generic name is derived from the Greek
pelor, "monster". He also emended the
specific name (honouring
William Conybeare) to
conybearei, but under the present rules of the
ICZN, the original
conybeari, today written without a capital, has priority. Mantell not only used the sauropod material of
C. brevis as the type of
Pelorosaurus conybeari but also a large
humerus 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 a
medullary cavity, showed that
Pelorosaurus was a land animal. This was a main motive in naming a separate genus; shortly afterwards, however, by studying the sacral vertebrae of
Cetiosaurus Mantell established that it too lived on land. Owen was highly piqued by Melville's and Mantell's attempts to "suppress" his
Cetiosaurus 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 epithet
brevis, "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 a
nomen nudum, to which he now assigned the sauropod material, making
Cetiosaurus 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 sole
holotype of
Pelorosaurus conybeari. Remarkably, in 1859 he repeated his mistake by again referring iguanodontid vertebrae, specimens NHMUK PV OR 1010 and OR 28635, to
C. brevis. The last of these he had in 1853 proposed to belong to
Pelorosaurus 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 name
Pelorosaurus had been connected with the
C. brevis material instead of with these finds. Owen's interpretation was commonly accepted until well into the twentieth century. By 1970 however, both
John Ostrom and
Rodney Steel understood that Owen's claim that
C. brevis in 1842 was still a
nomen nudum should be rejected as a transparent attempt to change the type specimen, inadmissible by present standards. By those same standards though, Melville's name change was also incorrect: as the name
Cetiosaurus brevis was still "available" he should simply have made the sauropod bones the
lectotype, removing the iguanodontid remains from the
syntype series. The sauropod bones, not the iguanodont bones, would then have retained the name
C. brevis. Therefore,
Cetiosaurus conybeari is a
junior objective synonym of
C. brevis, that is,
C. brevis is not only an older name, but one based on exactly the same fossils as the younger, invalid name. After 1850, more specimens continued to be assigned to both
Pelorosaurus and
Cetiosaurus, and both were studied and reported on extensively in the scientific literature. Slowly a tendency developed to subsume fragmentary sauropod material from the Jurassic of England under the designation
Cetiosaurus, while assigning incomplete European Cretaceous sauropod finds to
Pelorosaurus.
Pelorosaurus thus came to be a typical
wastebasket taxon for any European sauropod of this period. However, in recent years much work has been done to rectify the confusion. ==Classification==