Paranthodon

Paranthodon
Temporal range: Early Cretaceous, 145.5–136.4 Ma
Reconstruction of the skull, grey material is unknown.
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Clade: Dinosauria
Order: †Ornithischia
Clade: †Eurypoda
Suborder: †Stegosauria
Genus: †Paranthodon
Nopcsa, 1929[1]
Species: †P. africanus
Binomial name
Paranthodon africanus
Broom, 1912[2]
Synonyms[3]

Palaeoscincus africanus Broom, 1912
Paranthodon owenii Nopcsa, 1929

Paranthodon (pə-RAN-thə-don[4]) 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 British paleontologist Richard Owen initially identified the fragments as those of the pareiasaur Anthodon, after years of storage in the British Museum of Natural History, South African paleontologist Robert Broom identified the partial skull as belonging to a different genus, and named the specimen Palaeoscincus africanus. Several years later, Hungarian paleontologist Franz Nopcsa, unaware of Broom's new name, similarly concluded that it represented a new taxon, and named it 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 of the current binomial, Paranthodon africanus. The genus name combines the Ancient Greek para (near) with the genus name Anthodon, to represent the initial referral of the remains.

In identifying the remains as those of Palaeoscincus, Broom initially classified Paranthodon as an ankylosaurian, a statement backed by the research of Coombs in the 1970s. In 1929 however, Nopcsa identified the taxon as a stegosaurid, which most modern studies agree with. In 1981, the genus was reviewed with modern taxonomy, and found to be a valid genus of stegosaurid. However, a more recent 2008 review of Stegosauria could only identify one distinguishing feature, and while that study still referred it to Stegosauridae based on similarity, no diagnostic features of the family could be identified in Paranthodon.

Description

Size comparison between Paranthodon and a human

Paranthodon was a small relative of larger stegosaurids 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).[4][5] 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.[3]

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.[6] 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, but wear is absent on most teeth, similar to Huayangosaurus, meaning it is likely that Paranthodon lacked occlusion between teeth.[7] 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.[8] 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.[9]

Discovery and naming

Skull of Anthodon serrarius, to which the skull of Paranthodon was originally assigned

In 1845, amateur geologists William Guybon Atherstone and Andrew Geddes Bain discovered several fossils near Dassieklip, Cape Province, in the Bushmans River Valley.[10] This was the first dinosaur find in all of the Southern Hemisphere and Africa.[11] In 1849 and 1853, Bain sent some of the fossils to the Richard Owen for identification. Among them was an upper jaw Bain referred to as the "Cape Iguanodon", so the site was named "Iguanodonhoek". Atherstone published about the find in 1857,[10] 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.[12] Anthodon means "flower tooth".[13] 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.[3] 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.[3]

In 1909, 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.[2][12] 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.[2] In 1929, 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.[1][4][8] Due to present conventions, the specific name was later emended to owenii.[3] 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.[14] This makes Palaeoscincus africanus and Paranthodon owenii junior synonyms of Paranthodon africanus.[3]

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.[3] However, the teeth do not bear any autapomorphies of Paranthodon, and were referred to an indeterminate stegosaurid in 2008.[9]

Classification

Currently, Paranthodon is classified as a stegosaurus related to Stegosaurus, Tuojiangosaurus, and Loricatosaurus. Initially, when Broom assigned the name Palaeoscincus africanus to the Paranthodon fossils, he classified them as an ankylosaurian. This classification was later changed by Nopcsa, who found that Paranthodon best resembled a stegosaurid (before the group was truly defined[15]). Coombs (1978) did not follow Nopcsa's classification, keeping Paranthodon as an ankylosaurian, like Broom.[8] A subsequent review by Galton & Coombs in 1981 instead confirmed Nopcsa's interpretation, redescribing Paranthodon as a stegosaurid from the Late Cretaceous, .[3][6] Multiple phylogenetic analyses have placed Paranthodon in Stegosauria, and often in Stegosauridae. A 2010 analysis including nearly all species of stegosaurians found that Paranthodon was outside Stegosauridae, and in a polytomy with Tuojiangosaurus, Huayangosaurus, Chungkingosaurus, Jiangjunosaurus, and Gigantspinosaurus. However, when the latter two genera were removed, Paranthodon grouped with Tuojiangosaurus just outside Stegosauridae, and Huayangosaurus grouped with Chungkingosaurus in Huayangosauridae. Below is the analysis with all included genera.[16]

Hypothetical restoration based on related stegosaurians
Stegosauria

Gigantspinosaurus

Jiangjunosaurus

Chungkingosaurus

Huayangosaurus

Tuojiangosaurus

Paranthodon


Stegosauridae

Kentrosaurus

Loricatosaurus
Dacentrurinae

Dacentrurus

Miragaia



Stegosaurinae

Stegosaurus

Hesperosaurus

Wuerhosaurus








Other analyses have found Paranthodon closely related to Tuojiangosaurus, Loricatosaurus, and Kentrosaurus within Stegosaurinae.[9][17] Even though phylogenetic analyses recognize Paranthodon as a stegosaurid, the type material actually bears no synapomorphies of Stegosauria. However, the material is likely of stegosaurian nature, and phylogenies by many authors have found it to be within the group.[16]

Paleoecology

Map showing the Kirkwood Formation

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.[18] 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 136.4 million years ago.[4][8][19] A large variety of different animal groups have been found in the formation, including dinosaurs, at least two different sphenodontian lizards, multiple teleost fishes, a few crocodylians, some frog specimens, and also turtles. However, 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 and the primitive ornithomimosaurian Nqwebasaurus, the possible brachiosaurid Algoasaurus and a potential titanosaurian, and many ornithischians, Paranthodon, a genus of iguanodontian, and a "hypsilophodontid" (the family Hypsilophodontidae is no longer considered to be a natural grouping[20]).[18][21]

References

  1. 1 2 Nopsca, F. (1929). "Dinosaurierreste aus Siebenburgen V. Geologica Hungarica. Series Palaeontologica". Fasciculus. 4 (1): 13.
  2. 1 2 3 Broom, R. (1912). "Observations on some specimens of South African fossil reptiles preserved in the British Museum". Transactions of the Royal Society of South Africa. 2: 19–25. doi:10.1080/00359191009519357.
  3. 1 2 3 4 5 6 7 8 Galton, P.M.; Coombs, W.P. Jr. (1981). "Paranthodon africanus (broom) a stegosaurian dinosaur from the Lower Cretaceous of South Africa". Geobios. 14 (3): 299–309. doi:10.1016/S0016-6995(81)80177-5.
  4. 1 2 3 4 Holtz, T.R. Jr. (2007). Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages. Random House Books for Young Readers. p. 402. ISBN 978-0-375-92419-4.
  5. ↑ Holtz, T.R. Jr. (2014). "Supplementary Information to Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages". University of Maryland. Retrieved 2014-09-05.
  6. 1 2 Galton, P.M. (1981). "Craterosaurus pottonensis Seeley, a stegosaurian dinosaur from the Lower Cretaceous of England, and a review of Cretaceous stegosaurs". Neues Jahrbuch für Geologie und Paläontologie. 161 (1): 28–46. ISSN 0077-7749.
  7. ↑ Barrett, P.M. (2001). "Tooth Wear and Possible Jaw Action of Scelidosaurus harrisonii Owen and a Review of Feeding Mechanisms of Other Thyreophoran Dinosaurs". In Carpenter, Kenneth. The Armoured Dinosaurs. Indiana University Press. pp. 36–39. ISBN 0-253-33964-2.
  8. 1 2 3 4 Glut, D.F. (1997). Dinosaurs, the encyclopedia. McFarland & Co. pp. 676–677. ISBN 978-0-7864-7222-2.
  9. 1 2 3 Maidment, S.C.R.; Norman, D.B.; Barrett, P.M.; Upchurch, P. (2008). "Systematics and Phylogeny of Stegosauria (Dinosauria: Ornithischia)". Journal of Systematic Palaeontology. 6 (4): 367–407. doi:10.1017/S1477201908002459.
  10. 1 2 Atherstone, W.G. (1857). "Geology of Uitenhage". The Eastern Province Monthly Magazine. 1 (10): 518–532.
  11. ↑ Durand, J.F. (2005). "Major African contributions to Palaeozoic and Mesozoic vertebrate palaeontology". Journal of African Earth Sciences. 43 (2005): 71. doi:10.1016/j.jafrearsci.2005.07.014.
  12. 1 2 Owen, R. (1876). "Descriptive and illustrated catalogue of the fossil Reptilia of South Africa in the collection of the British Museum". Order of the Trustees: 14–15.
  13. ↑ Ruiz-López, H.; Pavón y Jiménez, J.A. (1789). "Flora Peruviana et Chilensis". Typis Gabrielis de Sancha. 1: 45.
  14. ↑ Coombs, W.P. Jr. (1978). "The Families of the Ornithischian Dinosaur Order Ankylosauria" (PDF). Palaeontology. 21 (1): 143–170.
  15. ↑ Sereno, P.C. (2005). "Stegosauridae". TaxonSearch: Database for Suprageneric Taxa & Phylogenetic Definitions. Retrieved 2014-10-02.
  16. 1 2 Maidment, S.C.R. (2010). "Stegosauria: a historical review of the body fossil record and phylogenetic relationships". Swiss Journal of Geological Sciences. 103 (2): 199–210. doi:10.1007/s00015-010-0023-3. ISSN 1661-8726.
  17. ↑ Galton, P.M. (2012). "Stegosauria". In Brett-Surman, Michael; Holtz, Thomas R. Jr.; Farlow, James O. The Complete Dinosaur. Indiana University Press. p. 486. ISBN 978-0-253-00849-7.
  18. 1 2 Forster, C.A.; Farke, A.A.; McCartney, J.A.; de Klerk, W.J.; Ross, C.F. (2009). "A "Basal" Tetanuran from the Lower Cretaceous Kirkwood Formation of South Africa". Journal of Vertebrate Paleontology. 29 (1): 283–285. doi:10.1671/039.029.0101. JSTOR 20491088.
  19. ↑ Pereda Suberbiola, X.; Galton, P.M.; Torcida, F.; Huerta, P.; Izquierdo, L.A.; Montero, D.; Pérez, G.; Urién, V. (2003). "First stegosaurian dinosaur remains from the Early Cretaceous of Burgos (Spain), with a review of Cretaceous stegosaurs". Revista Espanola de Paleontologia. 18 (2): 143–150. ISSN 0213-6937.
  20. ↑ Brown, C. M.; Evans, D. C.; Ryan, M. J.; Russell, A. P. (2013). "New data on the diversity and abundance of small-bodied ornithopods (Dinosauria, Ornithischia) from the Belly River Group (Campanian) of Alberta". Journal of Vertebrate Paleontology. 33 (3): 495. doi:10.1080/02724634.2013.746229.
  21. ↑ Chinsamy, A. (1997). "Albany Museum, Grahamstown, South Africa". In Currie, P.J.; Padian, K. Encyclopedia of Dinosaurs. Academic Press. p. 6. ISBN 978-0-12-226810-6.

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