Temporal range: Late Cretaceous,80–75Ma
Pinacosaurus ("plank lizard") is a genus of medium-sized ankylosaur dinosaurs that lived from the late Santonian to the late Campanian stages of the late Cretaceous Period (roughly 80–75 million years ago), in Mongolia and China. Pinacosaurus had between two and five additional holes near each nostril, which have not been explained.
Pinacosaurus was a lightly built, medium-sized ankylosaur that reached a length of 5 meters (16 ft) 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 Velociraptor. 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. 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. Its forelimb has five digits, and the phalangeal formula is 2-3-3-3-2, meaning that the innermost finger of the forelimb has two bones, the next has three, etc.
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. The holotype (AMNH 6523) is a partially crushed skull, jaws, and dermal bones collected in 1923.
Pinacosaurus is the best known Asian ankylosaur with more than 15 specimens, including one nearly complete skeleton, five skulls or partial skulls, and two finds of several juveniles huddled together, evidently killed by a sandstorm (Jerzykiewicz, 1993; Burns et al., 2011). The best skull belongs to a juvenile described by Teresa Maryanska in 1971 and 1977.
The type species of Pinacosaurus is P. grangeri. Young discovered a new specimen in the Ningxia Province, and described it as a new species P. ninghsiensis in 1935, but it is now considered to the same species as P. grangeri; as are fragmentary remains described as Syrmosaurus viminicaudus by Maleev in 1952. Arbour, Burns and Sissons (2009) considered Heishansaurus pachycephalus ("thick-headed Black Mountain lizard") from the Minhe Formation, near Heishan (= "Black Mountain"), Gansu Province, which is known from poorly preserved cranial and postcranial fragments, to be a junior synonym of P. grangeri as well. It was first described in 1953 as a pachycephalosaur and was usually considered a nomen dubium.
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. 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, Pinacosaurus is now considered to be an ankylosaurid. The cladogram below follows the most resolved topology from a 2011 analysis by paleontologists Richard S. Thompson, Jolyon C. Parish, Susannah C. R. Maidment and Paul M. Barrett.
- Arbour, V. M.; Burns, M. E.; Sissons, R. L. (2009). "A redescription of the ankylosaurid dinosaur Dyoplosaurus acutosquameus Parks, 1924 (Ornithischia: Ankylosauria) and a revision of the genus". Journal of Vertebrate Paleontology 29 (4): 1117. doi:10.1671/039.029.0405.
- Hill et al. 2003, p. 4.
- Gilmore 1933, p. 5 and Fig. 1.
- Hill et al. 2003.
- Martin, A.J. (2006). Introduction to the Study of Dinosaurs. Second Edition. Oxford, Blackwell Publishing. 560 pp. ISBN 1–4051–3413–5.
- Hill et al. 2003, p. 2–4.
- Gilmore 1933.
- Hill et al. 2003, p. 2.
- Young 1935.
- Hill et al., p. 2 refers to Maleev 1952.
- Gilmore 1933, p. 9.
- Thompson, R. S.; Parish, J. C.; Maidment, S. C. R.; Barrett, P. M. (2012). "Phylogeny of the ankylosaurian dinosaurs (Ornithischia: Thyreophora)". Journal of Systematic Palaeontology 10 (2): 301. doi:10.1080/14772019.2011.569091.
- 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 Novitates (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 Novitates (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.
- Burns, M. B.; Currie, P. J., Sissons, R. L., Arbour, V. M. (2011). "Juvenile specimens of Pinacosaurus grangeri Gilmore, 1933 (Ornithischia: Ankylosauria) from the Late Cretaceous of China, with comments on the specific taxonomy of Pinacosaurus.". Cretaceous Research 32 (2): 174–186. doi:10.1016/j.cretres.2010.11.007.