Pronunciation: pin-AK-o-SOR-us
Meaning: Plank lizard
Author/s: Gilmore (1933)
Synonyms: See below
First Discovery: Ömnögovi Province, Mongolia
Acta Ordinal: #172
Pinacosaurus grangeri
First described in 1933 from the Flaming Cliffs (Shabarakh Usu) of the Djadokhta Formation, Pinacosaurus is a small, desert-dwelling ankylosaurid recognised by its low, rectangular skull and extra openings in the snout, which vary from two to five pairs between individuals. Most known specimens are juveniles, whose slender shoulder blades and lightly built limbs contrast with the heavier proportions of older ankylosaurids. These fossils come from ancient dune-field environments that also preserved Protoceratops, Velociraptor, and the oviraptorids whose nesting sites made the region famous. Exceptionally preserved throat bones reveal the structure of the larynx, suggesting that this armoured dinosaur may have produced surprisingly bird-like vocalizations.
Pinacosaurus is equally notable for its remarkable juvenile bonebeds. At sites such as Alag Teeg and Bayan Mandahu, dozens of young individuals—some preserved in lifelike crouched poses—were found together, offering rare evidence that juvenile ankylosaurs travelled in groups, perhaps for protection in harsh desert landscapes. Their hands and feet are among the best preserved of any ankylosaur, showing five-fingered hands and three-toed feet, with a curious pattern of variable bone counts between individuals and even between the left and right limbs of the same animal. Adults, by contrast, are usually solitary finds. Combined with its distinctive skull, defensive tail club, and unusually well-documented growth stages, Pinacosaurus grangeri provides one of the clearest windows into ankylosaur biology, behaviour, and evolution in Late Cretaceous Asia.
Pinacosaurus is equally notable for its remarkable juvenile bonebeds. At sites such as Alag Teeg and Bayan Mandahu, dozens of young individuals—some preserved in lifelike crouched poses—were found together, offering rare evidence that juvenile ankylosaurs travelled in groups, perhaps for protection in harsh desert landscapes. Their hands and feet are among the best preserved of any ankylosaur, showing five-fingered hands and three-toed feet, with a curious pattern of variable bone counts between individuals and even between the left and right limbs of the same animal. Adults, by contrast, are usually solitary finds. Combined with its distinctive skull, defensive tail club, and unusually well-documented growth stages, Pinacosaurus grangeri provides one of the clearest windows into ankylosaur biology, behaviour, and evolution in Late Cretaceous Asia.
(Granger's plank lizard)Etymology
Pinacosaurus is derived from the Greek "pinak" (plank, small board, tablet) and "sauros" (lizard), referring to the small flat plates of armour covering the holotype skull.The species epithet, grangeri, honours discoverer Walter Wallis Granger. ZooBank registry: urn:lsid:zoobank.org:act:40854A99-ED96-42FD-86F7-BCC273E164F4. Syrmosaurus viminocaudus, named by Maleev in 1952, based on PIN AS 614 (a nearly complete skeleton lacking a skull), found at Bayn Dzak.
Pinacosaurus ninghsiensis ("from Ninghsia") was collected in the winter of 1932 by Professor P.L. Yuan—on his way back from Sinkiang as a member of the Sino-Swedish Expedition led by Dr. Sven Hedin—in what is now known as Ningxia Province in the North Alashan desert. It was described by C. C. Young in 1935. Pinacosaurus ninghsiensis is based on IVPP uncat. (a partial skeleton including a fragment of upper jaw, a partial right lower jaw, 23 vertebrae, a right shoulder blade, a right upper arm, a partial ischia, a right thigh, both shins, and two metatarsals), and is now considered to be a synonym of Pinacosaurus grangeri.
Ninghsiasaurus. In the English abstract at the end of a 1965 Chinese paper that briefly described the dermal plate of an indeterminate nodosaurid found close to Nanhsiung city, C. C. Young wrote that "it may belong to Pinacosaurus or Ninghsiasaurus...", and seemingly introduced the latter name as a new genus. That was almost certainly a lapsus calami—a slip of the pen—by Young, who intended to write Pinacosaurus ninghsiensis. Pinacosaurus ninghsiaensis (Young 1935 = spelling variant of Pinacosaurus ninghsiensis). Heishansaurus pachycephalus? ("thick-headed Black Mountain lizard") was discovered by Anders Birger Bohlin in the Minhe Formation, near Heishan ("Black Mountain"), Gansu Province, China, during a Sven Hedin led Sino-Swedish expedition to the North-Western provinces of China in 1930-1931. When Bohlin described its embarrisingly meagre fossils in 1953, he pointed out similarities to the "troodonts" Troödon (Leidy, 1856) and Pachycephalosaurus (Gilmore, 1931), which was weird for two reasons. Firstly, Troödon was ammended to Troodon (without the diaeresis) by Sauvage in 1876 and, secondly, in 1945 Charles Mortram Sternberg realised that Troodon (based on a single tooth) was a carnivore while Pachycephalosaurus was a herbivorous headbanger, and he shipped the latter, along with its bone-headed relatives, off to their own family, Pachycephalosauridae. As it happens, Bohlin had confused an armour plate for a thickened skull roof typical of pachycephalosaurs, not that it matters. Apart from the cast of one single back vertebra stored at the American Museum of Natural History with the inventory number AMNH 2062, the specimen is lost, and Heishansaurus (pronounced hay-shahn-sor-us) is considered a nomen dubium at worst and a poorly preserved specimen of Pinacosaurus grangeri at best.Discovery
The first remains of Pinacosaurus were discovered in the Djadokhta Formation at Shabarakh Usu, one of the classic localities within Bayn Dzak/Bayan Zag—an area known colloquially as "the Flaming Cliffs"—in Ömnögovi aimag (South Gobi Province), Mongolia, by Walter Granger, during the American Museum of Natural History's Central Asiatic Expedition in 1923.
The holotype (AMNH 6523) is a partially crushed skull, jaws, and a
few scattered bones and osteoderms.
Beyond the holotype, Pinacosaurus is known from multiple Mongolian localities, including Bayn Dzak sites worked by the Polish–Mongolian expeditions in 1964–1965 and 1970, further Bayn Dzak and Ulan Oshih specimens collected by the Maleev-era MPE teams in 1946–1948 and 1967–1968, Soviet–Mongolian localities at Shiljust-Ula, Baga-Tariach, and Alag Teeg from 1969–1970 and 1980–1989, rich HMNS–GIN sites at Tugrikin Shire, Alag Teeg, Toosgot, Zhinst Tolgoi, and Dzamin Khond excavated between 1992 and 2007, and two Ukhaa Tolgod localities—Camel's Humps and Death Row—excavated by AMNH–MAS teams in the 1990s and in 2005. Specimens of Pinacosaurus have also been found at nine localities in China, including Tianqiaotun—collected by Tan for the Geological Survey of China in 1923, a 1996 Sino-Belgian quarry at Bayan Mandahu, a Ningxia site—collected by P.L. Yuan in 1932, Bayan Tal at Alaten Obo, a non-specific SCDP Bayan Mandahu locality worked from 1988–1990, and four numbered Bayan Mandahu sites (63, 100, 101, 106) collected during the 1990 Sino-Canadian Dinosaur Project.
