Pelorosaurus ("monstrous lizard") is the generic name of a sauropod dinosaur. Pelorosaurus was one of the first sauropod names ever. Remains referred to Pelorosaurus date from the Early Cretaceous period, about 140-125 million years ago and have been found in England and Portugal.

Many species have been named in the genus but today these are largely seen as belonging to other genera. The first named species of Pelorosaurus, P. conybeari, is a junior synonym of Cetiosaurus brevis.


Pelorosaurus was the first sauropod 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 Taylor and Naish, is confusing to the extreme. In 1842 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, BMNH R2544–2547, and three chevrons, BMNH R2548–2550, found around 1825 by John Kingdon near Cuckfield in the Tunbridge Wells Sand Formation of the Hastings Beds, belonged to sauropods. Others however, among them perhaps the present specimen BMNH R10390 found near Sandown Bay on the Isle of Wight and BMNH R2133 and R2115 found near Hastings, actually belonged to some member of the Iguanodontidae. Noticing Owen's mistake in assigning iguanodont bones to Cetiosaurus, in 1849 comparative anatomist Alexander Melville renamed the sauropod bones Cetiosaurus conybeari.

Gideon Mantell in 1850 decided that C. conybeari was so different from Cetiosaurus that it needed a new genus, so he reclassified it under the new name Pelorosaurus Conybearei. 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 present rules 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, BMNH 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.

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.

In The Land Before Time

A Pelorosaurus briefly appears in The Land Before Time II: The Great Valley Adventure as part of a group of dinosaurs who are trying to re-seal the entrance to the Great Valley.