Пинакозавр: Доисторический ящер с панцирем из Азии

Genus of ankylosaurid dinosaur from Late Cretaceous

Pinacosaurus (meaning "Plank lizard") is a genus of ankylosaurid thyreophoran dinosaur that lived in Asia during the Late Cretaceous (Campanian, roughly 75 to 71 million years ago), mainly in Mongolia and China. The first remains of the genus were found in 1923, and the type species Pinacosaurus grangeri was named in 1933. Pinacosaurus mephistocephalus named in 1999, is a second possibly valid species differing from the type species in details of the skull armour. At least 24 Pinacosaurus skeletons have been found, possibly more than of any other ankylosaur. These predominantly consist of juveniles. Adult fossils have not been found in groups. Pinacosaurus was a medium sized ankylosaurine, about long and weighed up to Its body was flat and low slung but not as heavily built as in some other members of the Ankylosaurinae. The head was protected by bone tiles, hence its name. Each nostril was formed as a large depression pierced by between three and five smaller holes, the purpose of which is uncertain. A smooth beak bit off low growing plants that were sliced by rows of small teeth and then swallowed to be processed by the enormous hind gut. Neck, back and tail were protected by an armour of keeled osteoderms. The animal could also actively defend itself by means of a tail club.

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 (Bayn Dzak) were the original specimens of Pinacosaurus, found by Walter W. Granger in 1923. In 1933, Charles Whitney Gilmore named and described the type species Pinacosaurus grangeri. The generic name is derived from Greek πίναξ, pinax, "plank", in reference to the small rectangular scutes covering the head. The specific name honours Granger, who accompanied the 1923 expedition as a paleontologist. The holotype, AMNH 6523, was found in a layer of the Djadokhta Formation, dating from the Campanian. It consists of a partially crushed skull, lower jaws, the first two neck vertebrae, and dermal bones collected in 1923. The skull is still the largest known of the genus. In 1923, a well preserved sacrum with the attached right ilium and part of the presacral rod, caudal vertebrae, a left femur and a dermal scute was collected from the Wangshi Group in Shandong, China by H. C. T'an and Otto Zdansky and was described as Pinacosaurus cf. grangeri by Buffetaut (1995). Pinacosaurus is the best known Asian or worldwide ankylosaur with numerous specimens having been discovered. Because of the many finds, in principle the entire juvenile skeleton is known. Pinacosaurus especially provides information on the build of the ankylosaurian skull, as in the juveniles the head armour has not yet fused with the skull proper and the sutures of the various elements are still visible. Modern studies have not yet fully covered the abundance of data. A well preserved juvenile skull was described by Teresa Maryańska in 1971 and 1977. In 2003, Robert Hill studied the juvenile specimen IGM 100/1014. Also in 2011, the postcranial skeleton MPC 100/1305 was described in detail, though at the time referred to Saichania. Most recently, Michael Burns and colleagues described and illustrated the original Alag Teeg material from the Soviet Mongolian expeditions in 1969 and 1970.

Yang Zhongjian ("C. C. Young") discovered a new specimen in the Ningxia Province at the Bayan Mandahu Formation, and described it as a new species Pinacosaurus ninghsiensis in 1935. The rather complete skeleton lacks a present inventory number; it is now considered to be the same species as P. grangeri. The same is true of fragmentary remains, specimen PIN 614, described as Syrmosaurus viminocaudus by Evgenii Aleksandrovich Maleev in 1952. It was first described in 1953 as a pachycephalosaur and had been usually considered a nomen dubium. In 2015, Arbour and Currie again concluded it was a nomen dubium. In 1996, a Belgian Chinese expedition discovered a large and articulated skeleton in the Bayan Mandahu Formation. It was named as Pinacosaurus mephistocephalus, holotype specimen IMM 96BM3/1, by Pascal Godefroit et al. in 1999. The specific name is a contraction of Mephistopheles and Greek κεφαλή, kephalè, "head", in reference to the "devilish" squamosal horns. In 2010, Gregory S. Paul suggested that P. mephistocephalus were a junior synonym of P. grangeri. It was considered a valid species by Robert Hill in 2012, based on the "secondary dermal" (squamosal) horns and narial characteristics. In 1995, Eric Buffetaut referred ankylosaurian remains found in Shandong to a Pinacosaurus sp.

Pinacosaurus was a lightly built, medium sized animal, fully grown individuals reached a total length of Gregory S. Paul estimated its body mass at , However, some of these bones from the specimen were later reinterpreted as the larynx.

A juvenile specimen of Pinacosaurus preserves large paraglossalia (triangular bones or cartilages located in the tongue) which show signs of muscular stress, and it is thought this was a common feature of ankylosaurs. Pinacosaurus and other ankylosaurs likely relied heavily on muscular tongues and hyobranchia (tongue bones) when feeding, since their teeth were fairly small and were replaced at a relatively slow rate. Some modern salamanders have similar tongue bones, and use prehensile tongues to pick up food. Though Pinacosaurus may not have fed on fibrous and woody plants, they may have had a more varied diet, including tough leaves and pulpy fruits. Inversely, this might suggest ant eater like insectivorous behaviour.

In the group of juveniles found together at Bayan Mandahu, the individuals were all oriented into the same direction, suggesting they represent a travelling true herd simultaneously killed and covered by a sandstorm. It is remarkable that the members of such groups are all of about the same age, having an average length of circa 1.5 metres. This could be explained by the larger individuals being able to extract themselves from the sand, leaving the small members of the herd behind but in that case it is strange that no very young animals were found, the smallest being about one metre in length. The concentration of fossils at Alag Teeg has been explained as caused by a drying pool, but later research showed the sediments were deposited during a flood. During their ontogenetic development, in juveniles at first the ribs fused with their vertebrae. The forelimbs strongly increased in robustness, while the hindlimbs did not become larger relative to the rest of the skeleton, indicating that the arms bore most of the weight. In the cervical halfrings, the underlying bone band developed outgrowths connecting it with the underlying osteoderms, which simultaneously fused to each other. On the skull, the caputegulae first ossified at the snout and the rear rim; gradually the ossification extended towards the middle regions. On the rest of the body, the ossification process progressed from the neck onwards in the direction of the tail.

In 2023, a fossilized larynx was described from a specimen of P. grangeri by Norell and Yoshida et al. The larynx was composed of cricoid and arytenoid cartilages, similar to those of non avian reptiles. However its mobile cricoid arytenoid joint and long arytenoid cartilages would have enabled easy opening of the glottis, thus allowing air flow control similar to that of birds. Also, the cartilages were ossified, implying that laryngeal ossification is a feature of some non avian dinosaurs. This structure represents the oldest known example of a larynx preserved in a dinosaur, and suggests that Pinacosaurus was likely capable of making loud, possibly bird like vocalizations.

The habitat of Pinacosaurus consisted of a semi desert interspersed with oases. No large theropods are known to have inhabited the ecosystem, though smaller ones like Velociraptor were present. It has been suggested that the relatively light build of Pinacosaurus was an adaptation to gain agility to better fight small theropods, the moderately large club being fast enough to hit these swift targets.