Paranthodon

Paranthodon africanus Temporal range: Early Cretaceous, 145.5–136.4Ma PreꞒ Ꞓ O S D C P T J K Pg N
Skull reconstruction, white material is known. Unknown material reconstructed after related genera
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Dinosauria
Order:	†Ornithischia
Suborder:	†Stegosauria
Family:	†Stegosauridae
Subfamily:	†Stegosaurinae
Genus:	†Paranthodon Nopcsa, 1929
Binomial name
Paranthodon africanus Broom, 1912
Synonyms[1]
Palaeoscincus africanus Broom, 1912 Paranthodon owenii Nopcsa, 1929

Paranthodon (meaning "beside Anthodon"; "puh-RAN-thoh-don"^[2]) is a genus of stegosaurian dinosaur that lived in South Africa during the Early Cretaceous (approximately 145.5 to 136.4 million years ago). Discovered in 1845, it was one of the first stegosaurians found. Its only remains, including a partial skull and isolated teeth, were found in the Kirkwood Formation. Originally, the material was assigned to the pareiasaur Anthodon by Sir Richard Owen. After years of storage in the British Museum of Natural History, Robert Broom identified the partial skull as belonging to a different genus, and named the species Palaeoscincus africanus based on it. Many years later, Baron Franz Nopcsa, who did not know of Broom's paper, made similar conclusions. Nopsca named the new genus and species Paranthodon Owenii for the remains. However, since the Nopcsa's species was named after Broom's, and Broom did not assign a new genus, both names are now synonyms under Paranthodon africanus.

Thinking the material belonged to Palaeoscincus, Broom basically found Paranthodon to be ankylosaurian. Nopcsa however, found the genus to be stegosaurid, although no definition had yet been suggested. Even though Nopcsa's more recent paper found Paranthodon to be a stegosaurid, scientists followed Broom's classification without comment. Only in 1981, Peter Galton established that it was indeed a stegosaurid, this time in the modern sense. Paranthodon is one of a few genera from the Kirkwood Formation, most of which are unnamed, the only other named genera include the coelurosaurian Nqwebasaurus, and the possible camarasaurid Algoasaurus.

Discovery and naming

In 1845, amateur geologists William Guybon Atherstone and Andrew Geddes Bain found a number of fossils near Dassieklip, Cape Province, in the valley of the Bushmans River. In 1849 and 1853, Bain sent some 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". In 1857, Atherstone published about the find,^[3] but in 1871 lamented that it as yet had received no attention in London. Only in 1876 did Owen name a series of specimens from the collection as Anthodon serrarius.^[4] Anthodon means "flower tooth".^[5] Four specimens were assigned to Anthodon, the partial holotype skull BMNH 47337, the left jaw BMNH 47338, the matrix BNMH 47338 including bone fragments and impressions of the anterior skull, and the vertebrae BMNH 47337a.^[1] 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, the teeth were similar to those of Stegosauridae.^[1]

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 fossils of two entirely different species: a partial distorted skull, teeth and a mandible of a pareiasaur and a partial upper jaw of a dinosaur BMNH 47338.^[4][6] Broom kept the name Anthodon for the pareiasaur and identified the dinosaur fossil as belonging to the genus Palaeoscincus, naming the new species Paleoscincus africanus in 1912.^[6] In 1929 Baron Franz Nopcsa also studied the specimen, but unaware of Broom's publication, described a new dinosaurian taxon for the fossils, Paranthodon Owenii, with the specific name honouring Owen and the generic name meaning "near" or "besides" Anthodon.^[7][2] The specific name was capitalized, and was later corrected to owenii, which is present conventions.^[1] Only in 1978 Walter Coombs correctly combined both names into a Paranthodon africanus, as Paranthodon was the first new genus for the fossils, and africanus was the first named species.^[8] This makes both Palaeoscincus africanus and Paranthodon owenii junior synonyms of Paranthodon africanus.^[1]

The holotype of Paranthodon, BMNH 47338, was found in a layer of the Kirkwood Formation dating from the Berriasian-early Valanginian. 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.^[1]

Description

Restoration

Paranthodon was a small stegosaurid relative to larger relatives such as Stegosaurus. One estimate of its length, by Thomas R. Holtz Jr. found it to be 5.0 m (16.4 ft) long, and weighing generally between 454 and 907 kg (1,001 and 2,000 lb).^[2][9] The snout is elongated but 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. Of the skull, the 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 to Paranthodon. Even though their resemblance is great, tooth morphology is very distinguishing among stegosaurians, including Paranthodon. For example, cranial material is only known from Stegosaurus, Paranthodon, Kentrosaurus, and Tuojiangosaurus, and in all of them, the tooth morphology is a distinguishing feature.^[1]

Classification

Currently, Paranthodon is classified as a stegosaurid related to Stegosaurus, Tuojiangosaurus, and Loricatosaurus. However, when Broom named Palaeoscincus africanus, he assigned the material of Paranthodon to ankylosauria. This classification was later changed by Nopcsa, who found that Paranthodon best resembled a stegosaurid (before the group was truly defined^[10]). Subsequent authors after Nopcsa instead followed Broom's classification without comment. In 1981, Peter Galton reanalyzed the material of ankylosaurians and stegosaurians, and concluded that it was Nopcsa that was correct, finding Paranthodon to be a stegosaurid in the modern sense^[11] – All stegosaurians more closely related to Stegosaurus armatus than Huayangosaurus taibai.^[10] If so, it would be the second stegosaur discovered, after Regnosaurus, as well as being the first dinosaur found in South-Africa.^[12] This has been confirmed by multiple subsequent phylogenetic analyses, and according to a 2012 analysis it was found to be closely related to Tuojiangosaurus, Loricatosaurus, Stegosaurus, Wuerhosaurus, and Hesperosaurus within Stegosaurinae. The cladogram used by that study is shown below:^[13]

Even though phylogenetic analyses recover Paranthodon as a stegosaurid, the type material actually bears no synapomorphies of Stegosauria. However, the material is clearly of stegosaurian nature, and phylogenies by many authors have found it to be within the group.^[14]

Paleoecology

The Kirkwood Formation of South Africa is known from a few fossil remains of different species, of which Paranthodon was the first discovered.^[15] The formation is from the Early Cretaceous, and dates from 145.5 to 136.4 million years ago.^[2] The dinosaurian fauna consist of theropods, sauropods, ornithopods and Paranthodon, the only stegosaurian, with non-dinosaurian remains persisting to fragmentary and unnamed sphenodontians, fishes, crocodylians, frogs, and turtles. Few of the dinosaurs were named before 2009, with the oldest being Paranthodon. The theropods include a basal tetanuran, and the coelurosaurian Nqwebasaurus. As of 2009, the only ornithopod is an unnamed iguanodontian. One of the two sauropods is named, the possible camarasaurid Algoasaurus.^[15]

References

External links

• Thescelosaurus! on Paranthodon
• DinoData on Paranthodon