Regnosaurus

*Regnosaurus northamptoni*

**Regnosaurus** was a huayangosaurid stegosaurid dinosaur from Early Cretaceous England. Its jaws were very similar to Huayangosaurus' jaws. People thought that this was an iguanodontid, scelidosaurid, stegosaurid (but then it also included ankylosaurids), Hylaeosaurus synonym and sauropod. It was found to have been a stegosaurid in 1993.

## Discovery and Species

The fossil remains, a portion of the right lower jaw, were found near Cuckfield in Sussex, and made part of the collection of the British Museum of Natural History. In 1839 Gideon Mantell reported having noticed the fossil during a visit. Mantell soon came to the conclusion that the specimen represented the, until then unknown, lower jaw of his *Iguanodon*, probably that of a juvenile. On 8 February 1841 he presented it as such to the Royal Society. This interpretation was immediately challenged by Richard Owen, who felt that any proof of a connection was lacking. In 1848, after several real jaws of *Iguanodon* had been discovered, Mantell changed his position, concluding it was a related but different genus or subgenus, coining the name *Regnosaurus Northamptoni*. The generic name is derived from the Regni or Regnenses, a British tribe inhabiting Sussex. The specific name honours Spencer Compton, 2nd Marquess of Northampton, the president of the Royal Society, who was about to resign. By present conventions, the type species is written as *Regnosaurus northamptoni*.

*Regnosaurus* is known only from the holotype BMNH 2422, a right mandibular (lower jaw) fragment, consisting of a third of the dentary and a part of the splenial. The specimen is six inches long and shows fifteen tooth sockets. Also some replacement teeth are visible. Other bone fragments have sometimes been referred to *Regnosaurus*, such as a fossil pubis recovered on the Isle of Wight, but as these are of other parts of the body and a reasonably complete skeleton is lacking, the identity cannot be proven. The same is true for some dermal spikes reported by William Blows. *Regnosaurus* was probably a rather small animal, about 4 metres (13 feet) long.

Very little is known about it due to limited fossil material, with only parts of its jaw known. It is a part of the Huayangosauridae, a family of primitive stegosaurs primarily found in China and includes genera such as *Huayangosaurus* and *Chungkingosaurus*. Due to the sheer scarcity of the remains, even this classification is questionable and *Regnosaurus* is now regarded as a dubious genus.

In 1874, another genus of stegosaur from the same area was named *Craterosaurus*. Known only from a single vertebrae, it is possibly a synonym of *Craterosaurus*. However, currently both genera are classed as dubious.

## Phylogeny

First seen as some iguanodontid, *Regnosaurus* was later connected to armoured dinosaurs. In 1888 Richard Lydekker assigned it to the Scelidosauridae. In 1909 Friedrich von Huene classified it in the stegosaurian Omosauridae and in 1911 Alfred von Zittel assigned it to the Stegosauridae but these groups then had a different content and also included armoured forms. In 1956 Alfred Romer synonymised it with *Hylaeosaurus*. An entirely different suggestion was made by John Ostrom who surmised it might have been a sauropod.

The first to state that it was a stegosaurian in the modern sense was George Olshevsky in 1993. This was confirmed by Paul Barret and Paul Upchurch in 1995 who concluded that it is a stegosaur similar to *Huayangosaurus*, as the jaws are very similar. As the remains are so limited, many recent researchers have concluded *Regnosaurus* to be a nomen dubium.

## Appearance in other media

### *Jurassic Park*

* Regnosaurus is mentioned in the Jurassic World book "Dinosaur Digs".