Pinacosaurus

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Pinacosaurus

Extinct (fossil)

Scientific classification

Kingdom:	Animalia
Phylum:	Chordata
Class:	Sauropsida
Superorder:	Dinosauria
Order:	Ornithischia
Suborder:	Thyreophora
Infraorder:	Ankylosauria
Family:	Ankylosauridae
Subfamily:	Ankylosaurinae
Genus:	Pinacosaurus Gilmore 1933

Species

P. grangeri (type)
P. mephistocephalus Godefroit et al. 1999

Pinacosaurus ("plank lizard") is a genus a medium-sized ankylosaur dinosaurs from the late Santonian to the late Campanian stages of the late Cretaceous period, which lived roughly 75–80 million years ago in Mongolia and China. Pinacosaurus had between 2 and 5 additional holes near each nostril, which have not been explained.

1 Description
2 Discoveries
3 Classification
4 Footnotes
5 References

[edit] Description

Pinacosaurus was a lightly-built, medium-sized ankylosaur with a long skull, that reached a length of 5 meters (16 feet)^[1] Like all ankylosaurids, it had a bony club at the end of its tail which it used as a defensive weapon against predators such as Tarbosaurus. The most unusual element in the original specimen is the presence of two additional egg-shaped holes, one on top of the other, where the nostrils are normally found.^[2] The openings are characteristic of the genus, and the number varies: Godefroit et al. described four in 1999, and in 2003 a juvenile specimen with of five pairs of openings was described.^[3].

[edit] Discoveries

The American Museum of Natural History sponsored several Central Asiatic Expeditions to the Gobi Desert in Mongolia in the 1920s. Among the many paleontological finds from the "Flaming Cliffs" of the Djadokhta Formation in Shabarakh Usu were the original specimens of Pinacosaurus. ^[4] The holotype (AMNH 6523) is a partially crushed skull, jaws, and dermal bones collected in 1923.^[5]

Pinacosaurus is the best known Asian ankylosaur with more than 15 specimens, including one nearly complete skeleton, 5 skulls or partial skulls,^[6] including two finds of several juveniles huddled together, evidently killed by a sandstorm (Jerzykiewicz, 1993). The best skull belongs to a juvenile described by Maryanska in 1971 and 1977.

[edit] Classification

The original species is P. grangeri. Young discovered a new specimen in the Ningxia Province, and described it as a new species P. ninghsiensis in 1935,^[7] but it is now considered to the same species as P. grangeri; as are fragmentary remains described as Syrmosaurus viminicaudus by Maleev in 1952.^[8]

Additional remains from China described as P. mephistocephalus by Godefroit et al in 1999 are considered a valid species based on secondary dermal horns and narial characteristics.^[6] The best preserved skulls are from juveniles, but the holotype is an adult skull which is longer than it is wide, which indicates it may be a more basal thyreophoran.

Originally placed in the family Nodosauridae,^[9] it is now considered an ankylosaurid. An simplified cladogram of its current phylogenetic placement:^[10]

Ankylosauridae
- Gargoyleosaurus
  - Gastonia
    - Gobisaurus
      - Minmi
        
        Pinacosaurus
        
        Talarurus
        
        (Node M)
        
        (Node O)
        
        Shamosaurus
        
        Tsagantegia
        
        (Node N)
        
        (Node P)
        
        Tarchia
        
        Saichania
        
        Tianzhenosaurus
        
        Nodocephalosaurus
        
        Shanxia
        
        Ankylosaurus
        
        Euoplocephalus

[edit] Footnotes

^ Hill et al. 2003, p. 4.
^ Gilmore 1933, p. 5 and Fig. 1.
^ Hill et al 2003.
^ Hill et al. 2003, p. 2–4.
^ Gilmore 1933.
^ ^a ^b Hill et al. 2003, p. 2.
^ Young 1935.
^ Hill et al., p. 2 refers to Maleev 1952.
^ Gilmore 1933, p. 9.
^ Simplified from Hill et al. 2003, p. 16.

[edit] References

Dixon, Dougal. 'The Complete Book of Dinosaurs.' Hermes House, 2006.
Fukui Prefectural Dinosaur Museum : the web site — Pinacosaurus grangeri
Gilmore, C. W. (December 4, 1933). "Two new dinosaurian reptiles from Mongolia with notes on some fragmentary specimens". American Museum Novitiates (679): 1–20.
Hill, R. V.; Witmer, L. W.; Norell, M. A. (2003). "A New Specimen of Pinacosaurus grangeri (Dinosauria: Ornithischia) from the Late Cretaceous of Mongolia: Ontogeny and Phylogeny of Ankylosaurs". American Museum Novitiates (3395): 1–29.
Maleev, E. A. (1952). "Novoe semeystvo pantsirnich dinosavrov is verchnego mela Mongolii [A new family of armored dinosaurs from the Upper Cretaceous of Mongolia]". Doklady Akademii Nauk SSSR (87): 131–134. (Russian)
Young, C. C. (1935). "On a new nodosaurid from Ninghsia.". Palaeontologica Sinica, Series C (11): 5–27.