''Pinacosaurus'' (meaning "Plank lizard") is a
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
of
ankylosaurid
Ankylosauridae () is a family of armored dinosaurs within Ankylosauria, and is the sister group to Nodosauridae. The oldest known Ankylosaurids date to around 122 million years ago and went extinct 66 million years ago during the Cretaceous–Pal ...
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 body ...
n
dinosaur
Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...
that lived in
Asia
Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an area ...
during the
Late Cretaceous
The Late Cretaceous (100.5–66 Ma) is the younger 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 ''creta'', the ...
(
Santonian
The Santonian is an age in the geologic timescale or a chronostratigraphic stage. It is a subdivision of the Late Cretaceous Epoch or Upper Cretaceous Series. It spans the time between 86.3 ± 0.7 mya (million years ago) and 83.6 ± 0.7 mya. 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. Campanian s ...
, roughly 75 million to 71 million years ago), mainly in
Mongolia
Mongolia; Mongolian script: , , ; lit. "Mongol Nation" or "State of Mongolia" () is a landlocked country in East Asia, bordered by Russia to the north and China to the south. It covers an area of , with a population of just 3.3 million, ...
and
China
China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...
.
The first remains of the genus were found in 1923, and the
type species
In 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 species that contains the biological type specimen ...
''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. Of ''Pinacosaurus grangeri'' many skeletons have been found, more than of any other ankylosaur. These predominantly consist of juveniles that perhaps lived in herds roaming the desert landscape of their habitat.
''Pinacosaurus'' was a medium-sized ankylosaurine, about five metres long and weighed up to two tonnes. Its body was flat and low-slung but not as heavily built as in some other members of the
Ankylosaurinae
Ankylosaurinae is a subfamily of ankylosaurid dinosaurs, existing from the Early Cretaceous about 105 million years ago until the end of the Late Cretaceous, about 66 mya. Many genera are included in the clade, such as ''Ankylosaurus'', ''Pinacos ...
. The head was protected by bone tiles, hence its name. Each
nostril
A nostril (or naris , plural ''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 turbi ...
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 and extinct reptiles and amphibians, including lizards, crocodilians, frogs, temnospondyls (extinct ...
. The animal could also actively defend itself by means of a tail club.
Discovery and naming
![Pinacosaurus AMNH 6523 skull line](https://upload.wikimedia.org/wikipedia/commons/a/a0/Pinacosaurus_AMNH_6523_skull_line.png)
The
American Museum of Natural History
The American Museum of Natural History (abbreviated as AMNH) is a natural history museum on the Upper West Side of Manhattan in New York City. In Theodore Roosevelt Park, across the street from Central Park, the museum complex comprises 26 inter ...
sponsored several Central Asiatic Expeditions to the
Gobi Desert
The Gobi Desert (Chinese: 戈壁 (沙漠), Mongolian: Говь (ᠭᠣᠪᠢ)) () is a large desert or brushland region in East Asia, and is the sixth largest desert in the world.
Geography
The Gobi measures from southwest to northeast an ...
in Mongolia in the 1920s. Among the many paleontological finds from the "
Flaming Cliffs
The Flaming Cliffs site (also known as Bayanzag ( zh, 巴彥扎格), Bain-Dzak or Bayn Dzak) ( mn, Баянзаг ''rich in saxaul''), with the alternative Mongolian name of mn, Улаан Эрэг (''red cliffs''), is a region of the Gobi Desert ...
" of the
Djadokhta Formation
The Djadochta Formation (sometimes transcribed and also known as Djadokhta, Djadokata, or Dzhadokhtskaya) is a highly fossiliferous geological formation situated in Central Asia, Gobi Desert, dating from the Late Cretaceous period, about 75 milli ...
in Shabarakh Usu (Bayn Dzak) were the original specimens of ''Pinacosaurus'', found by
Walter W. Granger
Walter Willis Granger (November 7, 1872 – September 6, 1941) was an American vertebrate paleontologist who participated in important fossil explorations in the United States, Egypt, China and Mongolia.
Early life and career
Born in Midd ...
in 1923. In 1933,
Charles Whitney Gilmore
Charles Whitney Gilmore (March 11, 1874 – September 27, 1945) was an American paleontologist who gained renown in the early 20th century for his work on vertebrate fossils during his career at the United States National Museum (now the N ...
described a right ilium and a tail vertebra, without yet naming the animal. In a later publication of the same year, he named and described the
type species
In 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 species that contains the biological type specimen ...
''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 Specific name may refer to:
* in Database management systems, a system-assigned name that is unique within a particular database
In taxonomy, either of these two meanings, each with its own set of rules:
* Specific name (botany), the two-part (bino ...
honours Granger, who accompanied the 1923 expedition as a paleontologist. The
holotype
A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...
, 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. Campanian s ...
. 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.
''Pinacosaurus'' is the best known
Asia
Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an area ...
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 and China.
The first fossils of ''Saichania'' were found in the early 1970s in Mongolia. In 1977 the ty ...
''. At another site, Alag Teeg now considered part of the Alagteeg Formation
The Alagteeg Formation is a geological formation in Mongolia whose strata date back to the Late Cretaceous. Dinosaur remains are among the fossils that have been recovered from the formation.Weishampel et al., 2004, pp.593-600 It predominantly cons ...
, 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 region of the People's Republic of China. Its border includes most of the length of China's border with the country of Mongolia. Inner Mongolia also accounts for a ...
at the Bayan Mandahu Formation
The Bayan Mandahu Formation (also known as Wulansuhai Formation or Wuliangsuhai Formation) is a geological unit of "redbeds" located near the village of Bayan Mandahu in Inner Mongolia, China Asia ( Gobi Desert) and dates from the late Cretaceous ...
, 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
A dust storm, also called a sandstorm, is a meteorological phenomenon common in arid and semi-arid regions. Dust storms arise when a gust front or other strong wind blows loose sand and dirt from a dry surface. Fine particles are transporte ...
. 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
Teresa Maryańska (1937 – 3 October 2019) was a Polish paleontologist who specialized in Mongolian dinosaurs, particularly pachycephalosaurians and ankylosaurians. Peter Dodson (1998 p. 9) states that in 1974 Maryanska together with Halszka ...
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
Yang Zhongjian, also Yang Chung-chien (; 1 June 1897 – 15 January 1979), courtesy name Keqiang (), also known as C.C. (Chung Chien) Young, was a Chinese paleontologist and zoologist. He was one of China's foremost vertebrate paleontologists. H ...
("C. C. Young") discovered a new specimen in the Ningxia Province
Ningxia (,; , ; alternately romanized as Ninghsia), officially the Ningxia Hui Autonomous Region (NHAR), is an autonomous region in the northwest of the People's Republic of China. Formerly a province, Ningxia was incorporated into Gansu in 1 ...
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
Evgeny Aleksandrovich Maleev (, ; 25 February 1915 – 12 April 1966) was a Soviet and Russian paleontologist who did most of his research on reptiles and Asian fossils, such as the naming of the ankylosaur ''Talarurus'' and theropods ''Tarbo ...
in 1952.[ ]Arbour
Arbor(s) or Arbour(s) may refer to:
Arts and entertainment
* ''Arbor'' (installation), a 2013 public artwork in Indianapolis, Indiana, US
* Arbor, a counterweight-carrying device found in theater fly systems
* ''The Arbor'', a 1980 play by Andr ...
, Burns and Sissons (2009) considered ''Heishansaurus
''Heishansaurus'', meaning "Heishan lizard" after the area in China where it was discovered, is the name given to a dubious genus of herbivorous ornithischian dinosaur, probably belonging to the Ankylosauridae.
In 1930, Swedish palaeontologist A ...
pachycephalus'' ("thick-headed Black Mountain lizard") from the Minhe Formation
The Minhe Formation () is a geological formation in northwestern China, whose strata date back to the Late Cretaceous period.
Dinosaur remains are among the fossils that have been recovered from the formation.Weishampel, David B; et al. (2004). "D ...
, near Heishan (= "Black Mountain"), Gansu Province
Gansu (, ; alternately romanized as Kansu) is a province in Northwest China. Its capital and largest city is Lanzhou, in the southeast part of the province.
The seventh-largest administrative district by area at , Gansu lies between the Tibeta ...
, 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
Pachycephalosauria (; from Greek παχυκεφαλόσαυρος for 'thick headed lizards') is a clade of ornithischian dinosaurs. Along with Ceratopsia, it makes up the clade Marginocephalia. With the exception of two species, most pachyc ...
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 s ...
''. In 2015, Arbour and Currie again concluded it was a ''nomen dubium''.
In 1996, a Belgian
Belgian may refer to:
* Something of, or related to, Belgium
* Belgians, people from Belgium or of Belgian descent
* Languages of Belgium, languages spoken in Belgium, such as Dutch, French, and German
*Ancient Belgian language, an extinct language ...
-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 Pascal Godefroit is a Belgian paleontologist. He discovered dinosaurs like ''Olorotitan'' in 2003. Godefroit is the director of earth and life sciences at the Royal Belgian Institute of Natural Sciences
The Museum of Natural Sciences of Belgium ...
''et al.'' in 1999. The specific name is a contraction of Mephistopheles
Mephistopheles (, ), also known as Mephisto, is a demon featured in German folklore. He originally appeared in literature as the demon in the Faust legend, and he has since appeared in other works as a stock character (see: Mephistopheles in t ...
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, and more recently has examined sociology and theology. He is best known for his work and research on theropod dino ...
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
The given name Eric, Erich, Erikk, Erik, Erick, or Eirik is derived from the Old Norse name ''Eiríkr'' (or ''Eríkr'' in Old East Norse due to monophthongization).
The first element, ''ei-'' may be derived from the older Proto-Norse ''* ain ...
referred ankylosaurian remains found in Shandong
Shandong ( , ; ; alternately romanized as Shantung) is a coastal province of the People's Republic of China and is part of the East China region.
Shandong has played a major role in Chinese history since the beginning of Chinese civilizati ...
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, and more recently has examined sociology and theology. He is best known for his work and research on theropod dino ...
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
''Gobisaurus'' is an extinct genus of herbivorous basal ankylosaurid ankylosaur from the Upper Cretaceous (and possibly also the Lower Cretaceous) of China (''Nei Mongol Zizhiqu''). The genus is monotypic, containing only the species ''Gobisaur ...
'' and ''Shamosaurus
''Shamosaurus'' is an extinct genus of herbivorous basal ankylosaurid ankylosaur from Early Cretaceous (Aptian to Albian stage) deposits of Höövör, Mongolia.
Discovery and naming
In 1977, a Soviet-Mongolian expedition discovered the skeleto ...
'', 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
''Crichtonpelta'' is a genus of extinct herbivorous ankylosaurid dinosaur from the Late Cretaceous ( Cenomanian) of China.
Discovery and naming
In 2007, Lü Junchang, Ji Qiang, Gao Yubo and Li Zhixin named and described a second species of ''C ...
'' 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
The maxilla (plural: ''maxillae'' ) in vertebrates 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 t ...
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 nasal c ...
. 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. In tetrapods, it covers and protects the ends of long bones at the joints as articular cartilage, and is a structural component of many body parts including the rib cage, the neck an ...
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 archosauriforms, first appearing during the Triassic Period. Among extant archosaurs, birds ...
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
Teleostomi is an obsolete clade of jawed vertebrates that supposedly includes th ...
, otherwise unknown in dinosaurs, proving that the Ankylosauria had independently evolved from the Aetosauria
Aetosaurs () are heavily armored reptiles belonging to the extinct order Aetosauria (; from Greek, (aetos, "eagle") and (, "lizard")). They were medium- to large-sized omnivorous or herbivorous pseudosuchians, part of the branch of archosaurs ...
,[ 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 character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to have ...
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 vertebr ...
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.
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
Ankylosauridae () is a family of armored dinosaurs within Ankylosauria, and is the sister group to Nodosauridae. The oldest known Ankylosaurids date to around 122 million years ago and went extinct 66 million years ago during the Cretaceous–Pal ...
, ''Pinacosaurus'' had a bony club at the end of its tail which it likely used as a defensive weapon against predators
Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill the ...
. 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
The metatarsal bones, or metatarsus, are a group of five long bones in the foot, located between the tarsal bones of the hind- and mid-foot and the phalanges of the toes. Lacking individual names, the metatarsal bones are numbered from the medi ...
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, are a group of five long bones in the foot, located between the tarsal bones of the hind- and mid-foot and the phalanges of the toes. Lacking individual names, the metatarsal bones are numbered from the med ...
, 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 and extinct reptiles and amphibians, including lizards, crocodilians, frogs, temnospondyls (extinct ...
, 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, from the Late Jurassic to the Late Cretaceous period in what is now North America, South America, Europe, and Asia.
Description
Nodosaurids, like their close relatives the ankylosaurids, wer ...
by Gilmore,[ ''Pinacosaurus'' is now considered to be an ]ankylosaurid
Ankylosauridae () is a family of armored dinosaurs within Ankylosauria, and is the sister group to Nodosauridae. The oldest known Ankylosaurids date to around 122 million years ago and went extinct 66 million years ago during the Cretaceous–Pal ...
and a likely member of the Ankylosaurinae
Ankylosaurinae is a subfamily of ankylosaurid dinosaurs, existing from the Early Cretaceous about 105 million years ago until the end of the Late Cretaceous, about 66 mya. Many genera are included in the clade, such as ''Ankylosaurus'', ''Pinacos ...
. 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 with a skull that is longer than it is wide, which might cause a more basal position of the latter.
The following cladogram
A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to d ...
is based on the 2015 phylogenetic analysis
In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...
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
Anteater is a common name for the four extant mammal species of the suborder Vermilingua (meaning "worm tongue") commonly known for eating ants and termites. The individual species have other names in English and other languages. Together with ...
-like insectivorous
A robber fly eating a hoverfly
An insectivore is a carnivorous animal or plant that eats insects. An alternative term is entomophage, which can also refer to the human practice of eating insects.
The first vertebrate insectivores were ...
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.[
]
Paleoenvironment
The habitat
In ecology, the term habitat summarises the array of resources, physical and 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 ...
of ''Pinacosaurus'' consisted of a semi-desert
A semi-arid climate, semi-desert climate, or steppe climate is a dry climate sub-type. It is located on regions that receive precipitation below potential evapotranspiration, but not as low as a desert climate. There are different kinds of semi-ar ...
interspersed with oases
In ecology, an oasis (; ) is a fertile area of a desert or semi-desert environment'ksar''with its surrounding feeding source, the palm grove, within a relational and circulatory nomadic system.”
The location of oases has been of critical imp ...
. No large theropods are known to have inhabited the ecosystem
An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syste ...
, though smaller ones like ''Velociraptor
''Velociraptor'' (; ) is a genus of small dromaeosaurid dinosaur 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 the pa ...
'' 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 focused on the ankylosaurs, quadrupedal herbivorous dinosaurs who were protected by a covering bony plates and spikes and sometimes by a club ...
* Djadokhta Formation
The Djadochta Formation (sometimes transcribed and also known as Djadokhta, Djadokata, or Dzhadokhtskaya) is a highly fossiliferous geological formation situated in Central Asia, Gobi Desert, dating from the Late Cretaceous period, about 75 milli ...
* Evgeny Maleev
Evgeny Aleksandrovich Maleev (, ; 25 February 1915 – 12 April 1966) was a Soviet and Russian paleontologist who did most of his research on reptiles and Asian fossils, such as the naming of the ankylosaur ''Talarurus'' and theropods ''Tarbo ...
* Halszka Osmólska
Halszka Osmólska (September 15, 1930 – March 31, 2008) was a Polish paleontologist who had specialized in Mongolian dinosaurs.
Biography
She was born in 1930 in Poznań. In 1949, she began to study biology at Faculty of Biology and Earth Scie ...
* Teresa Maryańska
Teresa Maryańska (1937 – 3 October 2019) was a Polish paleontologist who specialized in Mongolian dinosaurs, particularly pachycephalosaurians and ankylosaurians. Peter Dodson (1998 p. 9) states that in 1974 Maryanska together with Halszka ...
References
{{Taxonbar, from=Q31422
Late Cretaceous dinosaurs of Asia
Djadochta fauna
Ankylosaurids
Taxa named by Charles W. Gilmore
Fossil taxa described in 1933
Ornithischian genera