''Tarchia'' (meaning "brainy one") 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 herbivorous ankylosaurid

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 ...

from 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 ...

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 ...

Discovery and naming

In 1970, a Polish-Mongolian expedition discovered an ankylosaurian skull near Khulsan. In 1977,

Teresa Maryańska Teresa Maryańska (1937 – 3 October 2019) was a Polish paleontologist who specialized in Mongolian dinosaurs, particularly pachycephalosaurians and ankylosaurians. She is considered not only as one of Poland's but also one of the world's leadin ...

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 ...

''Tarchia kielanae''. The generic name is derived from Mongolian тархи (''tarkhi'', "brain") and

Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

''~ia'', in reference to a brain size presumed larger than that of the related form ''

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 ...

''. The specific name honours Professor

Zofia Kielan-Jaworowska Zofia Emilia Kielan-Jaworowska (25 April 1925 – 13 March 2015) was a Polish paleobiologist. In the mid-1960s, she led a series of Polish-Mongolian paleontological expeditions to the Gobi Desert. She was the first woman to serve on the executi ...

, the leader of the expedition. 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 ...

, ZPal MgD-I/111, was discovered in the Upper

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

(possibly

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 ...

Maastrichtian The Maastrichtian ( ) is, in the International Commission on Stratigraphy (ICS) geologic timescale, the latest age (geology), age (uppermost stage (stratigraphy), stage) of the Late Cretaceous epoch (geology), Epoch or Upper Cretaceous series (s ...

)

Barun Goyot Formation The Baruungoyot Formation (also known as Barun Goyot) is a geological formation dating to the Late Cretaceous Period. It is located within and is widely represented in the Gobi Desert Basin, in the Ömnögovi Province of Mongolia. Descriptio ...

(previously known as the 'Lower Nemegt Beds') of the

Nemegt Basin The Nemegt Basin is a geographical area in the northwestern Gobi Desert, in Ömnögovi Province, southern Mongolia. It is known locally as the "Valley of the Dragons", since it is a Bone bed, source of many fossil finds, including dinosaurs, dino ...

of Mongolia. It consists of a skull roof, braincase and rear skull elements. Maryańska referred three additional specimens: ZPAL MgDI/43, a large postcranial skeleton containing three "free" tail vertebrae, twelve tail vertebrae of the "handle" of the tail club and a scute; ZPAL MgDI/49, a right humerus; and PIN 3142/251, a skeleton with skull, that as yet remains undescribed. ''Tarchia'' is the geologically youngest of all 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 ankylosaurid dinosaurs. In 1977,

Tatyana Tumanova Tatiana (or Tatianna, also romanized as Tatyana, Tatjana, Tatijana, etc.) is a female name of Sabine-Roman origin that became widespread in Eastern Europe. Origin Tatiana is a feminine, diminutive derivative of the Sabine—and later Latin� ...

named a second species: ''Tarchia gigantea''. This was a renaming of ''

Dyoplosaurus ''Dyoplosaurus'' (meaning “double-armoured lizard”) is a monospecific genus of ankylosaurid dinosaur from Alberta that lived during the Late Cretaceous (middle Campanian, ~76.5–75 Ma) in what is now the Dinosaur Park Formation. ''Dyoplosa ...

giganteus'' Maleev 1956, which had been based on specimen PIN 551/29. In 1987, Tumanova concluded that both species were identical. This would make ''Dyoplosaurus giganteus'' the senior synonym of ''Tarchia kielanae''. This was generally accepted and ''Tarchia gigantea'' became the usual

species name In taxonomy, binomial nomenclature ("two-term naming system"), also called binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, both of which use Latin grammatical forms, altho ...

, as a '' combinatio nova'' replacing ''Tarchia kielanae''. However, recent study by Victoria Megan Arbour indicates that ''D. giganteus'' is indistinguishable from other ankylosaurs from the late Campanian-Maastrichtian of Mongolia, and hence 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 ...

''; the study revived the name ''Tarchia kielanae''.Arbour, Victoria Megan, 2014. ''Systematics, evolution, and biogeography of the ankylosaurid dinosaurs.'' Ph.D thesis, University of Alberta. https://era.library.ualberta.ca/public/.../Arbour_Victoria_Spring2014.pdf Tarchia tumanovae holotype skeletal

A rump with tail and club, specimen ZPAL MgD I/113, once referred to ''Dyoplosaurus giganteus'' and subsequently to ''Tarchia gigantea'', was by Arbour seen as different from the ''D. giganteus'' holotype. The study by Arbour also concluded that specimen PIN 3142/250, in 1977 referred to ''Tarchia'' by Tumanova, probably belonged to ''Saichania'' instead. This would radically change the common image of ''Tarchia'' as this exemplar had been by far the best preserved and most illustrations, museum mounts and indeed scientific research had been based on it. Arbour discovered that the holotype of ''Tarchia'' shared distinguishing traits with that of ''

Minotaurasaurus ''Minotaurasaurus'' (meaning “Minos'-bull reptile”) is a monospecific genus of ankylosaurid dinosaur that lived in Mongolia during the Late Cretaceous (late Campanian stage, ~75-71 Ma) in what is now the Djadochta Formation. The type and only ...

'' Miles & Miles 2009, concluding that the latter is a

junior synonym In taxonomy, the scientific classification of living organisms, a synonym is an alternative scientific name for the accepted scientific name of a taxon. The botanical and zoological codes of nomenclature treat the concept of synonymy differently. ...

of ''Tarchia''. Subsequently, in 2016, a study conducted by Paul Penkalski and Tatiana Tumanova indicated that PIN 3142/250 is not referable to ''Saichania'' due to significant anatomical differences, but instead represents a new species of ''Tarchia'', ''T. teresae''. The study also recognized ''Minotaurasaurus'' as a distinct genus. In 2021, Jin-Young Park and team named a new species of ''Tarchia'', ''T. tumanovae'', known from the holotype MPC-D 100/1353 which consists of a partial skeleton with associated skull. It was found in the Nemegt Formation at the Hermiin Tsav locality, making it coeval with ''T. teresae''.

Description

''Tarchia'' was a medium-sized ankylosaur, measuring around long and weighing up to . If ZPAL MgD I/113 indeed belongs to the genus, it would have belonged to an individual measuring long. As an ankylosaurid, ''Tarchia'' would have had a broad, low-slung body, positioned on strong short legs. The body would have been protected by skin ossifications, named

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, ...

. It probably had a bony tail club, for active defence against predators. ''Tarchia'' had previously been distinguished from ''Saichania'' on the basis of its relatively larger basicranium, an unfused paroccipital process- quadrate contact and, based on PIN 3142/250, the fact that the

premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammals h ...

ry rostrum is wider than the maximum distance between the tooth rows in the maxillaries. In 2014, Arbour reported two distinguishing traits apart from those known exclusively from the holotype of ''Minotaurasaurus''; the back of the head is visible in top view; and a deep groove runs along the front and outer side of the squamosal horn, and at the front it surrounds around an accessory osteoderm placed on the rear supraorbital, forming a deep furrow. The 2016 redescription of ''Tarchia'' notes that it differs from ''Saichania'' in having a postorbital fossa (which separates the squamosal horn from the supraorbital) and an accessory osteoderm; the

occiput The occipital bone () is a cranial dermal bone and the main bone of the occiput (back and lower part of the skull). It is trapezoidal in shape and curved on itself like a shallow dish. The occipital bone lies over the occipital lobes of the ...

being visible in dorsal view; the large, deep braincase; the

foramen magnum The foramen magnum () is a large, oval-shaped opening in the occipital bone of the skull. It is one of the several oval or circular openings (foramina) in the base of the skull. The spinal cord, an extension of the medulla oblongata, passes thro ...

being higher than it is wide; and the nuchal osteoderms being taller laterally than medially. In addition, it differs from both ''Saichania'' and ''Minotaurasaurus'' in that it lacks postocular caputegulae (or small, polygonal bony plates behind the orbit) and has a proportionally high occiput in caudal view. The study additionally found that PIN 3142/250 (i.e. ''T. teresae'') can be distinguished from ''T. kielanae'' in that the accessory osteoderm is not fused to the roof of the skull, the quadrate and paroccipital process are not fused, the back of the skull roof is strongly sculptured, and the openings for the fourth to twelfth cranial nerves is bifurcated. Much information given about ''Tarchia'' in older work refers to PIN 3142/250 (which was briefly referred to ''Saichania'' until it was named as ''T. teresae'' in 2016). In 2001, it was stated that, in ''Tarchia'', wear

facet Facets () are flat faces on geometric shapes. The organization of naturally occurring facets was key to early developments in crystallography, since they reflect the underlying symmetry of the crystal structure. Gemstones commonly have facets cu ...

s indicative of tooth-to-tooth occlusion are present; this likely does not refer to the holotype specimen, since in the holotype no teeth are preserved.

Phylogeny

Vickaryous ''et al.'' in 2004 stated that ''Tarchia'' was basal to two distinct

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

s of Late Cretaceous ankylosaurids: one comprising

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

taxa In biology, a taxon (back-formation from ''taxonomy''; : taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular name and ...

(''

Ankylosaurus ''Ankylosaurus'' is a genus of Thyreophora, armored dinosaur. Its fossils have been found in geological formations dating to the very end of the Cretaceous Period (geology), Period, about 68–66 million years ago, in western North America, m ...

'', '' Euoplocephalus'') and the other comprising Asian taxa (''

Pinacosaurus ''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 genu ...

'' spp., ''

'', ''

Tianzhenosaurus ''Tianzhenosaurus'' (meaning “Tianzhen County, Tianzhen lizard”) is a genus of ankylosaurid dinosaurs known from the Late Cretaceous Huiquanpu Formation of Shanxi Province, China. The genus contains two species, ''T. youngi'' (the type species ...

'', '' Talarurus''). However, this was again based on PIN 3142/250, the characters of which usually defined the

operational taxonomic unit An operational taxonomic unit (OTU) is an operational definition used to classify groups of closely related individuals. The term was originally introduced in 1963 by Robert R. Sokal and Peter H. A. Sneath in the context of numerical taxonomy, wh ...

named ''Tarchia'' in the various

cladistic Cladistics ( ; from Ancient Greek 'branch') is an approach to biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is ...

analyses. Remarkably, ''Tarchia'' and ''Saichania'' nevertheless in these analyses often occupied very different positions. 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 a 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: A limited phylogenetic analysis conducted in the 2016 redescription of ''Tarchia'', focusing on the interrelationships between ''Tarchia'', ''Saichania'', and ''Minotaurasaurus'', is reproduced below.

Palaeobiology

The rocks in which ''Tarchia'' fossils were found likely represent eolian dunes and interdune environments, with small intermittent lakes and seasonal streams.

Feeding

''Tarchia'' was, like other Mongolian ankylosaurines,

herbivorous A herbivore is an animal anatomically and physiologically evolved to feed on plants, especially upon vascular tissues such as foliage, fruits or seeds, as the main component of its diet. These more broadly also encompass animals that eat n ...

and a low-level bulk feeder based on its sub-rectangular broad muzzle. Instead of oral processing, ankylosaurids living in dry environments such as ''Tarchia'' may have relied more on

hindgut fermentation Hindgut fermentation is a digestive process seen in monogastric herbivores (animals with a simple, single-chambered stomach). Cellulose is digested with the aid of symbiotic microbes including bacteria, archaea, and eukaryotes. The microbial fe ...

for digestion or, alternatively, consumed succulent plants that did not require complex chewing. These ankylosaurids may have also been restricted to simple orthal pulping and might have had to deal with more grit during feeding compared to ankylosaurs that lived in tropical to subtropical climates, as indicated by the microwear pits. Park ''et al.'' (2021) suggested that there was a shift from bulk feeding to selective feeding in Mongolian ankylosaurines during the Campanian and Maastrichtian stages which may have either been caused by the change in habitat, as the climate changed from semi-arid and arid to humid, or interspecific competition with

saurolophine Saurolophinae is a subfamily (biology), subfamily of hadrosaurid dinosaurs. It has since the mid-20th century generally been called the Hadrosaurinae, a group of largely non-crested hadrosaurs related to the crested sub-family Lambeosaurinae. How ...

hadrosaurids that immigrated from

Central Asia Central Asia is a region of Asia consisting of Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan, and Uzbekistan. The countries as a group are also colloquially referred to as the "-stans" as all have names ending with the Persian language, Pers ...

during the Campanian stage.

Pathology

One skull of ''Tarchia'' shows tooth marks identified as belonging to the tyrannosaurid, ''Tarbosaurus'', indicating the theropod hunted the ankylosaurid.Gallagher W.B., Tumanova T.A., Dodson P., Axel L., 1998, "CT scanning Asian ankylosaurs: paleopathology in a ''Tarchia'' skull", ''Journal of Vertebrate Paleontology'' 18: 44A-45A

References

External links

''Tarchia'' in the Dino Directory
{{Taxonbar, from=Q135304 Ankylosaurinae Dinosaur genera Campanian dinosaurs Baruungoyot Formation Nemegt Formation Maastrichtian dinosaurs Taxa named by Teresa Maryańska Fossil taxa described in 1977 Dinosaurs of Mongolia