Pelorosaurus (Monstrous lizard)
Pelorosaurus (Monstrous lizard)
Named By : Gideon Mantell - 1850
Diet : Herbivore
Size : Estimated 16 – 25 meters long
Type of Dinosaur : Sauropod
Type Species : P. conybeari (type)
Found in : England - Lower Greensand Group, Wealden Group, and France
When it Lived : Early Cretaceous, 125 million years ago
Pelorosaurus is a genus consisting of titanosauriform dinosaurs. The remains referred to as Pelorosaurus were found in England and Portugal during the Early Cretaceous period (around 140-125 millions years ago). Thomas Holtz estimated it to be 24 meters (79 feet) long.
Paul Upchurch, Philip D. Mannion, Michael P. Taylor, CC BY 2.5, via Wikimedia Commons
Pelorosaurus was the first name given to a sauropod. Although many species have been historically assigned to this genus, most of them are now considered to be part of other genera. P. conybeari is the junior synonym of Cetiosaurus Brevis.
Pelorosaurus was the very first dinosaur-like sauropod to have been identified. Richard Owen, who had found Cetiosaurus 1841, incorrectly thought it was a giant sea-going crocodile reptile. Mantell recognized Pelorosaurus to be a dinosaur that lived on land.
Reviewers Michael P. Taylor, Darren Naish and others noted that the taxonomic history for Cetiosaurus (and Pelorosaurus) is confusing. Richard Owen, an 1842 biologist, named several Cetiosaurus species. Cetiosaurus Brevis was one of them, and it was based on several specimens dating back to the Cretaceous Period. Four caudal vertebrae (BMNH R2544-2547) and three chevrons (BMNH R2548-2550), were found by John Kingdon around 1825 in the Tunbridge Sand Formation of the Hastings Beds. These were both likely to be sauropods. Other bones, such as BMNH R10390 found near Sandown Bay, Isle of Wight and BMNH R2133, R2115, were actually part of an iguanodont. Alexander Melville, a comparative anatomist, renamed the sauropod bones Cetiosaurus Conybeari after recognizing Owen’s error in assigning iguanodont bone to Cetiosaurus.
Gideon Mantell, a 1850s biologist, decided that C. conybeari was different than Cetiosaurus and needed a new Genus. He reclassified the animal under the new name Pelorosaurus conybeari. Mantell originally intended to name it “Colossosaurus” in November 1849. However, he realized that kolossos is Greek for “statue”, and not “giant”. The Greek pelor, “monster”, is the source of the generic name. He also emended his specific name (honouring William Conybeare), to conybearei. However, according to the current rules of the ICZN the original conybeari has priority. Mantell used not only the sauropod material C. brevis to create the type of Pelorosaurus Conybeari, but also a large humerus that Peter Fuller, a miller, found at the same location, BMNH 26626, which he believed to be the same individual. It was only a few meters from the vertebrae. Mantell purchased the bone to make PS8. Pelorosaurus was clearly a land animal as the humerus is clearly designed to support the body’s weight and has a medullary cavity. This was the main reason for naming a separate genera. However, shortly after, Mantell discovered that Cetiosaurus too lived on land by studying the sacral vertebrae.
Melville and Mantell tried to “suppress” Owen’s Cetiosaurus Brevis. Owen was very upset. He published a 1853 publication to correct the situation as he saw them. However, he did not have to admit to his original error. He suggested that Melville was motivated by the inaccuracy of Melville’s epithet Brevis, which means “short”, as the animal’s length could not be determined from its limited remains. Owen explained that anyone who is familiar with taxonomy will have realized that “short”, referred to individual vertebrae and not the entire animal. Owen implied on a page that the 1842 publication had not been sufficiently descriptive. He then gave Cetiosaurus Brevis a valid name. It was still not clear if Mantell had named it a new genera. Owen solved it by simply presenting Pelorosaurus conybeari’s humerus to be the only holotype. Surprisingly, Owen repeated the mistake in 1859 by referring to C. brevis iguanodontid verbrae, specimens BMNHR1010 and R28635, again. In 1853, he proposed that the last specimen belonged to Pelorosaurus. Owen said it was because Mantell had previously labeled them as such; Owen suggested that this mistake had been made by Owen who thought the Pelorosaurus name had been used with C. brevis material.
Owen’s interpretation was accepted by most people until the early 20th century. Rodney Steel and John Ostrom understood by 1970 that Owen’s claim in 1842 that C. Brevis was still a nomen Nudum should be rejected. This is a transparent attempt at changing the type specimen. It was not admissible under current standards. Melville’s name-change was also wrong. Since the Cetiosaurus Brevis name was still “available”, he should have simply made the sauropod bone the lectotype and removed the iguanodontid remnants from the syntype series. C. brevis would have been retained for the sauropod bones and not the iguanodont bone. Cetiosaurus conybeari, a junior objective synonym for C. Brevis, is therefore not only an older name but also one that is based on the exact same fossils as C. brevis’ invalid younger name.
More specimens were assigned to Pelorosaurus as well as Cetiosaurus after 1850. Both species were extensively studied and reported in the scientific literature. Slowly, a tendency began to develop to include fragmentary sauropod material of the Jurassic of England under Cetiosaurus while assigning incomplete European Cretaceous Sauropod finds as Pelorosaurus. Pelorosaurus was thus a common wastebasket taxon of any European sauropod from this period. However, much has been done in recent years to correct the confusion.