Temporal range: Early Cretaceous, 140Ma
|Skull reconstruction, white material is known|
Palaeoscincus africanus Broom, 1912
Paranthodon (meaning "beside Anthodon"; "puh-RAN-thoh-don") is a genus of stegosaurian ornithischian dinosaur that lived in South Africa in the Early Cretaceous. It was one of the first stegosaurians found, and lived between 145.5 and 136.4 million years ago. Its only remains, including a partial skull and some teeth, were found in the Kirkwood Formation, and were the first dinosaurs remains discovered there. Originally, the material was found associated with the non-dinosaurian genus Anthodon, and when Sir Richard Owen described the remains, he assigned the partial skull to Anthodon. After years of sitting in the British Museum of Natural History, Robert Broom identified that the partial skull belonged to a genus other than Anthodon, and named the species Palaeoscincus africanus for it. However, many years later, without knowing about Broom's paper Baron Franz Nopcsa found similar conclusions to Broom, but instead of finding it an ankylosaurian (as is Palaeoscincus), he found that the specimen represented stegosaurian remains. For the material Nopcsa named Paranthodon owenii (here written by present conventions) honoring Owen and the fact that the remains were found with Anthodon. However, because Broom first named the species, and Nopcsa created the genus, the binomial is now Paranthodon africanus, with both Palaeoscincus africanus and Paranthodon owenii junior synonyms.
Paleoscincus is an ankylosaurian genus, which Broom classified the material of Paranthodon in. Nopcsa however, thought Paranthodon was a member of the Stegosauridae in the older, more inclusive sense, related to Stegosaurus and Kentrosaurus. However, after Nopcsa's publication, many scientists still classified Paranthodon as an ankylosaurian without comment. Only in 1981 did one palaeontologist, Peter Galton establish that it was indeed a stegosaurid, this time in the modern sense. Many analyses have also come to the same or similar conclusions. Some features of Paranthodon are found only in stegosaurians, which is why is it classified with them. The partial skull of Paranthodon is not overly unique, however, when compared to other stegosaurians, it teeth distinguish it. 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 near Dassieklip, Cape Province, in the valley of the Bushmans River found a number of fossils. Bain in 1849 and 1853 sent some to the British paleontologist Richard Owen for identification. Among them was the upper jaw of what Bain thought was a dinosaur that he informally had indicated as the "Cape Iguanodon"; the site likewise was named "Iguanodonhoek". In 1857 Atherstone published about the find, but in 1871 lamented that it as yet had received no attention in London. Only in 1876 did Owen named a series of specimens as Anthodon serrarius. Anthodon means "flower tooth".
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: those of a member of the Pareiasauria and a dinosaur jaw. Broom kept the name Anthodon for the pareiasaur and identified the dinosaur fossil as belonging to the genus Palaeoscincus, naming in 1912 the new species Paleoscincus africanus. In 1929 Baron Franz Nopcsa also studied the specimen. Unaware of Broom's publication he basically drew the same conclusions but also named a new genus coining for the dinosaur the name Paranthodon Oweni. The generic name means "near" or "besides" (para in Greek) Anthodon. The specific name honours Owen. In his publication Nopcsa by mistake also used the spelling variant Paranthodon Owenii. By present conventions the name should be written as Paranthodon oweni. Only in 1978 Walter Coombs correctly combined both names into a Paranthodon africanus. This makes both Palaeoscincus africanus and Paranthodon owenii junior synonyms of Paranthodon africanus.
The holotype, BMNH 47337, was found in a layer of the Kirkwood Formation dating from the Berriasian-Valanginian. It consists of the back of the snout, containing the maxilla with teeth, the posterior caudodorsal ramus of the premaxilla and part of the nasals. Four other specimens can also be distinguished by these, and are therefore referred to Paranthodon, BMNH 47338, BMNH 47338b, BMNH 47337a, and BMNH 49992. They include a partial left mandible with teeth, a matrix with impressions, three vertebrae, and some teeth, respectively.
Paranthodon was a smaller stegosaurid compared to Stegosaurus. One estimate of its length, by Thomas R. Holtz Jr. found it being 5.0 m (16.4 ft) long, with a weight approximately equal to a horse, between 454 and 907 kg (1,001 and 2,000 lb), although this estimate is quite general. The snout is elongated but not extremely so and convex on top; the back of the premaxilla is long and broad; the external nares are large. The teeth have a prominent primary ridge. Of the skull, the nasal and maxilla 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 there 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.
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 an ankylosaurian. This classification was later changed by Nopcsa, who found that Paranthodon best resembled a stegosaurid (in the older, more inclusive sense). Subsequent authors after Nopcsa, however, followed Broom's classification without comment. In 1981, Peter Galton reanalyzed the material of ankylosaurians and stegosaurian, and concluded that it was Nopcsa that was correct, finding Paranthodon to be a stegosaurid in the modern sense. If so, it would be about five metres long and be the second stegosaur discovered, after Regnosaurus, as well as being the first dinosaur found in South-Africa. This has been concluded in multple phylogenetic analyses, and according to a recent analysis it would be closely related to Tuojiangosaurus, Loricatosaurus, Stegosaurus, Wuerhosaurus, and Hesperosaurus within Stegosaurinae. The resulting cladogram is shown below:
The Kirkwood Formation of Africa is known from a few fossil remains of different species, of which Paranthodon was the first discovered. The formation is from the Early Cretaceous, and dates from 145.5 to 136.4 million years ago. Theropods, sauropods, ornithopods and the only stegosaurian, Paranthodon, consist of the dinosaurian fauna, with the only non-dinosaurian remains persisting to the fragmentary and unnamed sphenodontians, fishes, crocodylians, frogs, and turtles. A 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.
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