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''Pinacosaurus'' (meaning "Plank lizard") is a
genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
of ankylosaurid
thyreophora Thyreophora ("shield bearers", often known simply as "armored dinosaurs") is a group of armored ornithischian dinosaurs that lived from the Early Jurassic until the end of the Cretaceous. Thyreophorans are characterized by the presence of bod ...
n
dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...
that lived in
Asia Asia ( , ) is the largest continent in the world by both land area and population. It covers an area of more than 44 million square kilometres, about 30% of Earth's total land area and 8% of Earth's total surface area. The continent, which ...
during the
Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''cre ...
(
Campanian The Campanian is the fifth of six ages of the Late Cretaceous epoch on the geologic timescale of the International Commission on Stratigraphy (ICS). In chronostratigraphy, it is the fifth of six stages in the Upper Cretaceous Series. Campa ...
, roughly 75 to 71 million years ago), mainly in
Mongolia Mongolia is a landlocked country in East Asia, bordered by Russia to the north and China to the south and southeast. It covers an area of , with a population of 3.5 million, making it the world's List of countries and dependencies by po ...
and
China China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...
. The first remains of the genus were found in 1923, and the
type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...
''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 A nostril (or naris , : nares ) is either of the two orifices of the nose. They enable the entry and exit of air and other gasses through the nasal cavities. In birds and mammals, they contain branched bones or cartilages called turbinates ...
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 Osteoderms are bony deposits forming scales, plates, or other structures based in the dermis. Osteoderms are found in many groups of Extant taxon, extant and extinct reptiles and amphibians, including lizards, crocodilians, frogs, Temnospondyli, ...
. The animal could also actively defend itself by means of a tail club.


Discovery and naming

The
American Museum of Natural History The American Museum of Natural History (AMNH) is a natural history museum on the Upper West Side of Manhattan in New York City. Located in Theodore Roosevelt Park, across the street from Central Park, the museum complex comprises 21 interconn ...
sponsored several Central Asiatic Expeditions to the
Gobi Desert The Gobi Desert (, , ; ) is a large, cold desert and grassland region in North China and southern Mongolia. It is the sixth-largest desert in the world. The name of the desert comes from the Mongolian word ''gobi'', used to refer to all of th ...
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 In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...
''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 A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...
, AMNH 6523, was found in a layer of the Djadokhta Formation, dating from the
Campanian The Campanian is the fifth of six ages of the Late Cretaceous epoch on the geologic timescale of the International Commission on Stratigraphy (ICS). In chronostratigraphy, it is the fifth of six stages in the Upper Cretaceous Series. Campa ...
. 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 Shandong is a coastal Provinces of China, province in East China. Shandong has played a major role in Chinese history since the beginning of Chinese civilization along the lower reaches of the Yellow River. It has served as a pivotal cultural ...
,
China China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...
by H. C. T'an and Otto Zdansky and was described as ''Pinacosaurus
cf. The abbreviation cf. (short for either Latin or , both meaning 'compare') is generally used in writing to refer the reader to other material to make a comparison with the topic being discussed. However some sources offer differing or even contr ...
grangeri'' by Buffetaut (1995). ''Pinacosaurus'' is the best known
Asia Asia ( , ) is the largest continent in the world by both land area and population. It covers an area of more than 44 million square kilometres, about 30% of Earth's total land area and 8% of Earth's total surface area. The continent, which ...
n or worldwide ankylosaur with numerous specimens having been discovered. From the original Flaming Cliffs or Shabarakh Usu several other fossils have been reported including ZPAL MgD II/1: a nearly complete skeleton; ZPAL MgD II/9: a postcranial skeleton; ZPAL MgD II/31: the handle of a tail club; and PIN 3780/3: a skull; PIN 614: a nearly complete postcranial skeleton (= ''Syrmosaurus viminocaudus''); and possibly MPC 100/1305, a postcranial skeleton erroneously described in 2011 as belonging to ''
Saichania ''Saichania'' (Mongolian meaning "beautiful one") is a genus of herbivorous ankylosaurid dinosaur from the Late Cretaceous period of Mongolia. The first fossils of ''Saichania'' were found in the early 1970s in Mongolia. In 1977 the type speci ...
''. At another site, Alag Teeg now considered part of the Alagteeg Formation, entire bonebeds have been uncovered of juvenile animals. Soviet-Mongolian expeditions in 1969 and 1970 reported thirty skeletons. Mongolian-Japanese expeditions added another thirty between 1993 and 1998. Forty were reported by Canadian expeditions between 2001 and 2006. The remains have not been all dug up and it is possible the reports partly pertain to the same material. In
Inner Mongolia Inner Mongolia, officially the Inner Mongolia Autonomous Region, is an Autonomous regions of China, autonomous region of China. Its border includes two-thirds of the length of China's China–Mongolia border, border with the country of Mongolia. ...
at the Bayan Mandahu Formation, the Canada−China Dinosaur Project in 1987, 1988, and 1990 found specimens IVPP V16853: a skull with cervical halfrings; IVPP V16283: a partial skull, IVPP V16854: a nearly complete skeleton; IVPP V16346: a partial skull; and IVPP V16855: a skeleton. Other, as yet undescribed material included two finds of several juveniles huddled together, evidently killed by a sandstorm. Whereas ankylosaur skeletons have often been preserved laying on their back, most ''Pinacosaurus'' juveniles are found on their belly in a resting position, with the legs tucked in. 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. In 2011, Currie published a study on the hand and foot, body parts often incompletely known with other ankylosaurs. The same year Michael Burns dedicated an article to four juveniles from the Bayan Mandahu. 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.


Additional species and synonyms

Yang Zhongjian ("C. C. Young") discovered a new specimen in the
Ningxia Province Ningxia, officially the Ningxia Hui Autonomous Region, is an Autonomous regions of China, autonomous region in Northwestern China. Formerly a Provinces of China, province, Ningxia was incorporated into Gansu in 1954 but was later separated from ...
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.
Arbour Arbor(s) or Arbour(s) may refer to: Arts and entertainment * Arbor (installation), ''Arbor'' (installation), a 2013 public artwork in Indianapolis, Indiana, US * Arbor, a counterweight-carrying device found in theater fly system#Arbors, fly syste ...
, Burns and Sissons (2009) considered '' Heishansaurus pachycephalus'' ("thick-headed Black Mountain lizard") from the Minhe Formation, near Heishan (= "Black Mountain"),
Gansu Province Gansu is a provinces of China, province in Northwestern China. Its capital and largest city is Lanzhou, in the southeastern part of the province. The seventh-largest administrative district by area at , Gansu lies between the Tibetan Plateau, Ti ...
, 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 had been usually considered a ''
nomen dubium In binomial nomenclature, a ''nomen dubium'' (Latin for "doubtful name", plural ''nomina dubia'') is a scientific name that is of unknown or doubtful application. Zoology In case of a ''nomen dubium,'' it may be impossible to determine whether a ...
''. 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 Mephistopheles ( , ), also known as Mephostophilis or Mephisto, is a demon featured in German folklore, originating as the chief devil in the Faust legend. He has since become a stock character appearing in Mephistopheles in the arts and popular ...
and Greek κεφαλή, ''kephalè'', "head", in reference to the "devilish" squamosal horns. In 2010,
Gregory S. Paul Gregory Scott Paul (born December 24, 1954) is an American freelance researcher, author and illustrator who works in paleontology. He is best known for his work and research on theropoda, theropod dinosaurs and his detailed illustrations, both l ...
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. Arbour and Michael Burns have confirmed that the species was valid. In 1995, Eric Buffetaut referred ankylosaurian remains found in
Shandong Shandong is a coastal Provinces of China, province in East China. Shandong has played a major role in Chinese history since the beginning of Chinese civilization along the lower reaches of the Yellow River. It has served as a pivotal cultural ...
to a ''Pinacosaurus'' sp.


Description


Size and distinguishing traits

''Pinacosaurus'' was a lightly built, medium-sized animal, fully grown individuals reached a total length of .Genus List for Holtz 2012
/ref>
Gregory S. Paul Gregory Scott Paul (born December 24, 1954) is an American freelance researcher, author and illustrator who works in paleontology. He is best known for his work and research on theropoda, theropod dinosaurs and his detailed illustrations, both l ...
estimated its body mass at , while
Thomas R. Holtz Thomas Richard Holtz Jr. (born September 13, 1965) is an American vertebrate palaeontologist, author, and principal lecturer at the University of Maryland, College Park, University of Maryland's Department of Geology. He has published extensively ...
estimated it to have a body mass of a horse. The postcranial skeleton PIN 614 measures from the first neck vertebrae to the end of the tail. In 2015, Arbour and Currie established some distinguishing traits of the genus. The upper snout armour does not consist of distinct tiles, ''caputegulae'', but of a fused mass. Adult individuals have a skull that is longer than wide. This trait is shared with the distant relatives '' Gobisaurus'' and '' Shamosaurus'', but ''Pinacosaurus'' differs from those in the possession of extra openings in the nostril and a pointy protruding ''caputegula'' on the prefrontal, directed to the front. ''Pinacosaurus'' differs from '' Crichtonpelta'' in the lack of an ornamented rear edge of the skull roof and in the cheek horn not being curved upwards. Arbour and Currie also provided a list of traits in which ''P. grangeri'' and ''P. mephistocephalus'' differed from each other. ''P. grangeri'' has a notch in the snout armour just above the innermost nostril opening. ''P. mephistocephalus'' has squamosal horns extending to behind beyond the rear of the skull roof, their points representing the widest point of the skull, instead of the upper rims of the eye sockets. ''P. mephistocephalus'' also has a clear transverse narrowing of the skull roof at level of the lacrimals, just in front of the eye sockets. It had been suggested that the rear skull roof of ''P. mephistocephalus'' was more convex but Arbour and Currie concluded it essentially had the same curvature. The holotype of ''P. mephistocephalus'' has very long cheek horns but a juvenile specimen, MPC 100/1344, found as part of a ''P. grangeri'' group, shows a similar elongation.


Skull

The adult skulls known have a length of about thirty centimetres. ''Pinacosaurus'' has exceptionally smooth praemaxillae, front snout bones, forming the bone core of the upper beak, that was in life covered with a horn sheet. The
maxilla In vertebrates, the maxilla (: maxillae ) is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The two maxil ...
bears about fourteen teeth. A typical and remarkable element of ankylosaurine skulls is that the nostril is in the shape of a large "narial vestibule" in which several smaller oval holes are present. With ''Pinacosaurus'' there are at least three per side. Gilmore already noticed this configuration in the original specimen. To allow a comparison between the holes of the several ankylosaurine species, they have been dubbed "A", "B" and "C". The top hole A seems to access the main air-passage of the
nasal cavity The nasal cavity is a large, air-filled space above and behind the nose in the middle of the face. The nasal septum divides the cavity into two cavities, also known as fossae. Each cavity is the continuation of one of the two nostrils. The nas ...
. In ''P. grangeri'' this hole is visible in top view through a notch in the snout armour, whereas in ''P. mephistocephalus'' the armour overhangs the hole. The opening pattern is characteristic of the genus: in ''Pinacosaurus'' the C hole is below the A hole and the B opening is on the lower outer side of the vestibule. In ''Pinacosaurus'' juveniles the C hole seems to consist of secondary smaller openings of varying number: Godefroit ''et al.'' described four pairs of openings in total in 1999, and in 2003 a juvenile specimen with five pairs of openings was described. The extra C openings have been named C2 and C3. The precise function of this arrangement is unclear. There are several chambers in the praemaxilla and maxilla to which these holes are connected but it has also been suggested that some extra holes are the result of damage. The larger number with juveniles could be explained by
cartilage Cartilage is a resilient and smooth type of connective tissue. Semi-transparent and non-porous, it is usually covered by a tough and fibrous membrane called perichondrium. In tetrapods, it covers and protects the ends of long bones at the joints ...
sheets not having been ossified yet. The visible sutures of the skull elements in juvenile specimens allowed for the first time to determine their precise arrangement. They generally consisted of indistinctly formed simple shapes. Several skull openings like the
antorbital fenestra An antorbital fenestra (plural: fenestrae) is an opening in the skull that is in front of the eye sockets. This skull character is largely associated with Archosauriformes, archosauriforms, first appearing during the Triassic Period. Among Extant ...
and the temporal fenestrae apparently closed at a very young age for they are no longer visible even in the juveniles found. The squamosal horn does not cover the entire squamosal, creating the illusion that an additional skull bone is present in front of the horn. Maryańska in 1977 thought that this was a
tabular bone The tabular bones are a pair of triangular flat bones along the rear edge of the skull which form pointed structures known as tabular horns in primitive Teleostomi. References Fish anatomy Amphibian anatomy {{vertebrate-anatomy-stub ...
, otherwise unknown in dinosaurs, proving that the Ankylosauria had independently evolved from the Aetosauria, a hypothesis today entirely discarded. Godefroit in 1999 called it a "secondary dermal squamosal". A real distinctive trait is that the quadratojugal touches the postorbital, whereas in other Thyreophora for which the condition is known, these bones are separated by the jugal. Usually it is assumed that this configuration is not unique for ''Pinacosaurus'' but a
synapomorphy In phylogenetics, an apomorphy (or derived trait) is a novel Phenotypic trait, character or character state that has evolution, evolved from its ancestral form (or Plesiomorphy and symplesiomorphy, plesiomorphy). A synapomorphy is an apomorphy sh ...
of the Ankylosauridae as a whole. In 2015, a juvenile specimen was described showing a complex
hyoid bone The hyoid-bone (lingual-bone or tongue-bone) () is a horseshoe-shaped bone situated in the anterior midline of the neck between the chin and the thyroid-cartilage. At rest, it lies between the base of the mandible and the third cervical verte ...
or tongue bone apparatus. It included paraglossalia at the sides, paired first and second ceratobranchials and higher epibranchials. Also the bone structure suggested that in the middle a cartilaginous basihyal was present. The strong development of the hyoid would indicate that a powerful tongue compensated for the weakly developed dentition. It was inferred that all dinosaurs had such complex tongue bones but that these were generally lost during fossilisation. However, some of these bones from the specimen were later reinterpreted as the
larynx The larynx (), commonly called the voice box, is an organ (anatomy), organ in the top of the neck involved in breathing, producing sound and protecting the trachea against food aspiration. The opening of larynx into pharynx known as the laryngeal ...
.


Postcranial skeleton

The postcranial skeleton of the known fossils is rather lightly built. Most of these represent juveniles, however: even specimen IMM 96BM3/1, the ''P. mephistocephalus'' holotype, is no longer than about . Juveniles had four rear back vertebrae fused into a "sacral rod", three true sacrals, and a tail base of seven vertebrae possessing transverse processes. Behind these about eight "free" vertebrae are present, followed by about twenty vertebrae stiffened by projections and forming the "handle" of the tail club. Like all ankylosaurids, ''Pinacosaurus'' had a bony club at the end of its tail which it likely used as a defensive weapon against predators. This club was relatively small. The torso is very flat. The forelimbs are moderately robust; the ''P. mephistocephalus'' holotype has a quite robust humerus and ulna, however. The hand is completely known, which is exceptional for ankylosaurids. It 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 metatarsals are closely appressed and held vertical. The claws are hoof-shaped. In the pelvis, the ilia flare strongly outwards to the front. The ischium is thin and curves forwards. The hindlimbs are moderately robust. The shinbone has a wide underside with well-formed condyles. Currie therefore assumed that the lower leg articulated directly with the
metatarsus The metatarsal bones or metatarsus (: metatarsi) are a group of five long bones in the midfoot, located between the tarsal bones (which form the heel and the ankle) and the phalanges ( toes). Lacking individual names, the metatarsal bones are ...
, the inner part of the astragalus and the entire calcaneum being absent or non-ossified cartilage elements. As in all known ankylosaurids, the foot has three toes, not four as Maryańska assumed in 1977, misled by the damaged specimen ZPAL MgD−II/9. The phalangeal formule of the toes is variable: most individuals have 0−3−3−4−0 but some exemplars possess an extra penultimate phalanx in the third toe, resulting in 0-3-4-4-0, while others lack a phalanx in the fourth toe, which causes a 0-3-3-3-0 configuration. The configuration of the skin ossifications, or
osteoderms Osteoderms are bony deposits forming scales, plates, or other structures based in the dermis. Osteoderms are found in many groups of Extant taxon, extant and extinct reptiles and amphibians, including lizards, crocodilians, frogs, Temnospondyli, ...
, of the body is partly known: no single specimen conserves a complete set. Additional information can be gleaned from the larger specimen MPC 100/1305, a possible ''Pinacosaurus'' exemplar. The neck is protected by two cervical halfrings, consisting of keeled rectangular segments fused to an underlying bone band. This band is completely ossified even in juvenile individuals. Godefroit assumed ''Pinacosaurus'' differed from other species in having three or four segments instead of the usual six, but Arbour concluded that the normal number was in fact present. The sides of the rump and the tail were occupied by moderately long, flat, recurved, triangular spikes. Parallel rows of smaller oval keeled osteoderms were present on the back. A continuous "sacral shield" on the hip, made of fused plates, is absent.


Classification

Originally placed in the
Nodosauridae Nodosauridae is a family of ankylosaurian dinosaurs known from the Late Jurassic to the Late Cretaceous periods in what is now Asia, Europe, North America, and possibly South America. While traditionally regarded as a monophyletic clade as the ...
by Gilmore, ''Pinacosaurus'' is now considered to be an ankylosaurid and a likely member of the Ankylosaurinae. As indicated by Thompson et al. 2012, the difference in the relative position of the two ''Pinacosaurus'' species between the respective analyses, is influenced by the fact that the best preserved ''P. grangeri'' skulls are from juveniles, while the holotype of ''P. mephistocephalus'' is an adult. The following
cladogram A cladogram (from Greek language, Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an Phylogenetic tree, evolutionary tree because it does not s ...
is based on the 2015
phylogenetic analysis In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical data ...
of the Ankylosaurinae conducted by Arbour and Currie:


Paleobiology


Diet

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 A robber fly eating a hoverfly An insectivore is a carnivorous animal or plant which eats insects. An alternative term is entomophage, which can also refer to the human practice of eating insects. The first vertebrate insectivores we ...
behaviour.


Growth

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.


Vocalization

In 2023, a fossilized
larynx The larynx (), commonly called the voice box, is an organ (anatomy), organ in the top of the neck involved in breathing, producing sound and protecting the trachea against food aspiration. The opening of larynx into pharynx known as the laryngeal ...
was described from a specimen of ''P. grangeri'' by Norell and Yoshida ''et al''. The larynx was composed of
cricoid The cricoid cartilage , or simply cricoid (from the Greek ''krikoeides'' meaning "ring-shaped") or cricoid ring, is the only complete ring of cartilage around the Vertebrate trachea, trachea. It forms the back part of the larynx, voice box and fun ...
and
arytenoid cartilage The arytenoid cartilages () are a pair of small three-sided pyramids which form part of the larynx. They are the site of attachment of the vocal cords. Each is pyramidal or ladle-shaped and has three surfaces, a base, and an apex. The arytenoid ...
s, 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.


Paleoenvironment

The
habitat In ecology, habitat refers to the array of resources, biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species' habitat can be seen as the physical manifestation of its ...
of ''Pinacosaurus'' consisted of a semi-desert interspersed with oases. No large theropods are known to have inhabited the
ecosystem An ecosystem (or ecological system) is a system formed by Organism, organisms in interaction with their Biophysical environment, environment. The Biotic material, biotic and abiotic components are linked together through nutrient cycles and en ...
, though smaller ones like ''
Velociraptor ''Velociraptor'' (; ) is a genus of small dromaeosaurid dinosaurs that lived in Asia during the Late Cretaceous epoch, about 75 million to 71 million years ago. Two species are currently recognized, although others have been assigned in th ...
'' 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.


See also

*
Timeline of ankylosaur research This timeline of ankylosaur research is a chronological listing of events in the History of paleontology, history of paleontology focused on the ankylosaurs, quadrupedal herbivorous dinosaurs who were protected by a covering bony plates and spik ...
* Djadokhta Formation * Evgeny Maleev * Halszka Osmólska * Teresa Maryańska


References

{{Taxonbar, from=Q31422 Ankylosaurinae Dinosaur genera Campanian dinosaurs Djadochta Formation Taxa named by Charles W. Gilmore Fossil taxa described in 1933 Dinosaurs of Mongolia Dinosaurs of China