Paranthodon

*Paranthodon africanum*

***Paranthodon*** is a genus of extinct stegosaurian dinosaur that lived in South Africa during the Early Cretaceous, approximately 145.5–136.4 million years ago. Discovered in 1845, it was one of the first stegosaurians found. Its only remains, a partial skull and isolated teeth, were found in the Kirkwood Formation. Although Owen initially identified the fragments as those of the pareiasaur *Anthodon*, after years of storage in the British Museum of Natural History, Broom identified the partial skull as belonging to a different genus, and named the specimen *Palaeoscincus africanus*. Several years later, Nopcsa, unaware of Broom's new name, similarly concluded that it represented a new taxon, and named the binomial *Paranthodon owenii*. However, since the Nopcsa's species name was assigned after Broom's, and Broom did not assign a new genus, both names are now synonyms under the current naming, *Paranthodon africanus*. The genus name was chosen from the Ancient Greek para, "near" and *Anthodon*, for the originally proposed similarity of the specimens.

In identifying the remains as those of *Palaeoscincus*, Broom basically classified *Paranthodon* as an ankylosaurian, a statement backed by the research of Coombs. Nopcsa however, identified the genus as a stegosaurid, which most modern studies agree with. In 1981, the genus was reviewed, and found to be a valid genus of stegosaurid. *Paranthodon* is one of a few genera found in the Kirkwood Formation; other such taxa include theropods, like *Nqwebasaurus*; ornithopods; such as Iyuku and sauropods, like *Algoasaurus*.

## Discovery and naming

In 1845, amateur geologists William Guybon Atherstone and Andrew Geddes Bain discovered several fossils near Dassieklip, Cape Province, in the Bushmans River Valley. This was the first dinosaur find in all of the Southern Hemisphere and Africa. In 1849 and 1853, Bain sent some of the fossils to the British paleontologist Richard Owen for identification. Among them was an upper jaw Bain referred to as the "Cape *Iguanodon*"; as such the site was named "Iguanodonhoek". Atherstone published about the find in 1857, but lamented in 1871 that it had thus far received no attention in London. Only in 1876 did Owen name a series of specimens from the collection as *Anthodon serrarius*. *Anthodon* means "flower tooth". The partial holotype skull BMNH 47337, the left jaw BMNH 47338, the matrix BMNH 47338 including bone fragments and impressions of the anterior skull, and the vertebrae BMNH 47337a were all assigned to *Anthodon*. In 1882, Othniel Charles Marsh assigned *Anthodon* to Stegosauridae based on BMNH 47338, and in 1890, Richard Lydekker found that although *Anthodon* was a pareiasaur, its teeth were similar to those of Stegosauridae.

In 1909, the South-African paleontologist Robert Broom visited the collection of the British Museum of Natural History. He concluded that Owen had mixed the partial distorted skull, teeth, and a mandible of a pareiasaur and a partial upper jaw of a dinosaur BMNH 47338, which were actually from two different species. Broom kept the name *Anthodon* for the pareiasaur, but identified the other fossil as a member of the genus *Palaeoscincus*, naming the new species *Paleoscincus africanus* in 1912. He found that the anatomy of the teeth were quite different, even thought they resembled each other, as well as those of *Stegosaurus*. In 1929, Baron Franz Nopcsa, unaware of Broom's previous publication, provided a new name for Broom's *P. africanus*, as D.M.S. Watson believed that the jaw should be differentiated from *Anthodon*. Nopcsa named the species *Paranthodon Owenii*, with the genus name derived from the Latin para, meaning "similar", "near", or "beside", and Anthodon, and specific name honoring Owen. Due to present conventions, the specific name was later emended to *owenii*. In 1978, Walter Coombs incorporated both names into the current nomenclature, *Paranthodon africanus*, as *Paranthodon* was the first new genus for the fossils and *africanus* was the first named species. This makes *Palaeoscincus africanus* and *Paranthodon owenii* junior synonyms of *Paranthodon africanus*.

The holotype of *Paranthodon*, BMNH 47338, was found in a layer of the Kirkwood Formation dated between the Berriasian and early Valanginian ages. It consists of the back of the snout, containing the maxilla with teeth, the posterior caudodorsal ramus of the premaxilla, part of the nasals, and some isolated teeth probably from the lower jaw. One additional specimen can be assigned to it based on the dentition, BMNH 47992, including only isolated teeth sharing the same morphology as those from the holotype. However, the teeth do not bear any autapomorphies of *Paranthodon*, and were referred to an indeterminate stegosaurid in 2008.

## Description

*Paranthodon* was a small stegosaurid relative to larger relatives such as *Stegosaurus*. Thomas R. Holtz Jr. estimated that the animal was 5.0 m (16.4 ft) long and weighed between 454 and 907 kg (1,001 and 2,000 lb). The snout is elongated, though not extremely so, and convex on top. The back of the premaxilla is long and broad, and the external nares are large. The teeth have a prominent primary ridge. The fossilized nasal and maxillary bones are relatively complete, and an incomplete premaxilla is also preserved. The partial snout resembles *Stegosaurus* in its large posterior premaxillary process and the extension of the palate. However, *Stegosaurus* is the only stegosaurid known from adequate cranial material to compare with *Paranthodon*, and even though their resemblance is great, tooth morphology is very distinguishing among the stegosaurians. For example, cranial material is only known from *Stegosaurus*, *Paranthodon*, *Kentrosaurus*, and *Tuojiangosaurus*, and in all of them, the tooth morphology differs.

The maxilla of *Paranthodon* preserves the tooth row, and shows that there is little to no overhang. This differs from ankylosaurians, where there is a large amount of overhang of the maxilla. The teeth also have a middle ridge, with five fewer prominent ridges on either side. This is similar to the size ridges seen on *Kentrosaurus*. Like all stegosaurians, the denticles on the teeth are rounded at the tips, in contrast to ankylosaurians. Also, like *Huayangosaurus*, but unlike *Kentrosaurus* and *Stegosaurus*, *Paranthodon* possesses a prominent buccal margination (a ridge beside the tooth row). *Paranthodon* teeth preserve wear, possibly cause by rubbing with other teeth. However, wear is absent on most teeth, similar to *Huayangosaurus*, meaning it is likely that *Paranthodon* lacked occlusion between teeth. *Paranthodon* is distinguished from other stegosaurs by a long, wide, posterior process of the premaxilla, teeth in the maxilla with a very large cingulum, and large ridges on the tooth crowns. Not all of these features were considered valid in a 2008 review of Stegosauria, with the only autapomorphy found being the possession of a partial second bony palate on the maxilla.

## Classification

Although known from fragmentation of the jaw they are enough to tell that it was a stegosaur.

## Paleoecology

The Kirkwood Formation is in South Africa, and many fossils of different species and genera have been discovered in it, with Paranthodon being the first uncovered. The formation is of a Late Jurassic to Early Cretaceous age, with the oldest deposits from the Tithonian, about 145.5 million years ago, and the youngest rocks being from the Valanginian, about 130 million years ago. The specific vertebrate-bearing portion of the formation is approximately level with the upper region of the Sundays River Formation, which has been dated to 139 to 131 mya based on microfossils. A large variety of different animal groups have been found in the formation, including dinosaurs, at least two different sphenodontian tuataras, multiple teleost fishes, a few crocodylians, some frog specimens, and also turtles. A large amount of the material of the Kirkwood formation only includes isolated teeth or partial and fragmentary pieces of bone. Dinosaurs of the formation include a basal tetanuran, the primitive ornithomimosaurian Nqwebasaurus, the sauropod Algoasaurus, a potential titanosaurian, many ornithischians, a genus of ornithopod Iyuku, and a "hypsilophodontid" (the family Hypsilophodontidae is no longer considered to be a natural grouping). Multiple additional sauropod taxa have been discovered, including a basal eusauropod, a brachiosaurid, a dicraeosaurid and a derived diplodocid.
If the referral of teeth from Ethiopia to Paranthodon is correct, then the taxon's geographic range is extended significantly. The Mugher locality is approximately 151 million years old, about 14 million older than has previously been suggested for Paranthodon, as well as across both southern and eastern Africa. The fauna in the Mugher locality differ from elsewhere of the same time and place in Africa. While the Tendaguru has abundant stegosaurs, sauropods, ornithopods and theropods, the Mugher Mudstone preserves the stegosaur Paranthodon, a hypsilophodontid ornithopod, a probable sauropod, and theropods related to Allosauridae and Dromaeosauridae.

## JPInstitute.com Description

Paranthodon was a close relative of Stegosaurus and lived in the southern part of Africa at the end of the Jurassic period. The stegosaurs were a family of plant-eaters with small heads and a row of either plates or spines running along their back from their neck to the end of their tail.

Paranthodon was initially classified in 1929 as a non-dinosaur due to the lack of material - only a partial jaw with teeth were found. It was given its present name in 1978, but classified as an ankylosaur. In 1979 a number of similarities with Stegosaurus were noted and it was given its current membership in the stegosauria.

## Links

http://web.archive.org/web/20040606013918fw\_/http://www.jpinstitute.com/dinopedia/dinocards/dc\_paran.html
https://web.archive.org/web/20080720024640/http://kids.yahoo.com/dinosaurs/292--Paranthodon