''Shamosaurus'' is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

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 basal ankylosaurid

ankylosaur Ankylosauria is a group of herbivorous dinosaurs of the clade Ornithischia. It includes the great majority of dinosaurs with armor in the form of bony osteoderms, similar to turtles. Ankylosaurs were bulky quadrupeds, with short, powerful l ...

from

Early Cretaceous The Early Cretaceous (geochronology, geochronological name) or the Lower Cretaceous (chronostratigraphy, chronostratigraphic name) is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 143.1 ...

(

Aptian The Aptian is an age (geology), age in the geologic timescale or a stage (stratigraphy), stage in the stratigraphic column. It is a subdivision of the Early Cretaceous, Early or Lower Cretaceous epoch (geology), Epoch or series (stratigraphy), S ...

Albian The Albian is both an age (geology), age of the geologic timescale and a stage (stratigraphy), stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early Cretaceous, Early/Lower Cretaceous epoch (geology), Epoch/s ...

stage) deposits of Höövör,

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 1977, a Soviet-Mongolian expedition discovered the skeleton of an unknown ankylosaurian at the Hamrin-Us site in

Dornogovi Province Dornogovi (, ''East Gobi'') is one of the 21 aimags (provinces) of Mongolia. It is located in the southeast of the country, bordering PR China's autonomous region of Inner Mongolia. Dornogovi is located in the Gobi Desert and frequent sand- and ...

. This was the first discovery of an ankylosaur in the

Lower Cretaceous Lower may refer to: * ''Lower'' (album), 2025 album by Benjamin Booker * Lower (surname) * Lower Township, New Jersey *Lower Receiver (firearms) * Lower Wick Gloucestershire, England See also * Nizhny {{Disambiguation ...

of Mongolia.T.A. Tumanova, 1983, "Pervyy ankilozavr iz nizhnego mela Mongolii", In: L.P. Tatarinov, R. Barsbold, E. Vorobyeva, B. Luvsandanzan, B.A. Trofimov, Yu. A. Reshetov, & M.A. Shishkin (eds.), ''Iskopayemyye reptilii mongolii''. Trudy Sovmestnaya Sovetsko-Mongol'skaya Paleontologicheskaya Ekspeditsiya 24: 110-118 In

1983 1983 saw both the official beginning of the Internet and the first mobile cellular telephone call. Events January * January 1 – The migration of the ARPANET to TCP/IP is officially completed (this is considered to be the beginning of the ...

, Tatyana Tumanova 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 ...

''Shamosaurus scutatus''. The generic name is derived from

Mandarin Mandarin or The Mandarin may refer to: Language * Mandarin Chinese, branch of Chinese originally spoken in northern parts of the country ** Standard Chinese or Modern Standard Mandarin, the official language of China ** Taiwanese Mandarin, Stand ...

''sha mo'', "sand desert", the Chinese name for the Gobi. The specific name means "protected by a shield" in

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 ...

, a reference to the body armour. ''Shamosaurus'' is known from 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 ...

PIN N 3779/2, collected from the Dzunbain Formation, equivalent to the Khukhtekskaya Formation and dating from the

, about 115 million years old. It consists of a complete

skull The skull, or cranium, is typically a bony enclosure around the brain of a vertebrate. In some fish, and amphibians, the skull is of cartilage. The skull is at the head end of the vertebrate. In the human, the skull comprises two prominent ...

, lower

jaw The jaws are a pair of opposable articulated structures at the entrance of the mouth, typically used for grasping and manipulating food. The term ''jaws'' is also broadly applied to the whole of the structures constituting the vault of the mouth ...

s and partial postcranial skeleton with armor. Only the skull was described in 1983. Later the specimens PIN 3779/1, a skull piece, and PIN 3101, a lower jaw, were referred. The fossils are part of the collection of the Palaeontological Institute at

Moscow Moscow is the Capital city, capital and List of cities and towns in Russia by population, largest city of Russia, standing on the Moskva (river), Moskva River in Central Russia. It has a population estimated at over 13 million residents with ...

. The holotype skull is exhibited there, together with two cervical halfrings.

Description

''Shamosaurus'' was a medium-sized ankylosaurian. 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 ...

estimated its body length at 5 metres (16 ft), its weight at 2 tonnes (2.2 short tons). In 2012 Holtz gave a higher estimation of 7 meters (23 ft). In 2014, Victoria Megan Arbour gave a revised list of distinguishing traits. The

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, ...

on the skull roof are not very pronounced nor separated as distinctive ''caputegulae'', head tiles. The squamosal horns on the rear skull corners are short and slightly rounded. The quadratojugal horn on the cheek has its apex in the middle. The rear rim of the skull roof has no clear (nuchal) processes.Arbour, Victoria Megan, 2014. ''Systematics, evolution, and biogeography of the ankylosaurid dinosaurs''. Ph.D thesis, University of Alberta ''Shamosaurus scutatus'' shares many

cranial Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek language, Greek roots, describe something in its standard anatomical position. Thi ...

similarities with '' Gobisaurus domoculus'', including a rounded

squamosal The squamosal is a skull bone found in most reptiles, amphibians, and birds. In fishes, it is also called the pterotic bone. In most tetrapods, the squamosal and quadratojugal bones form the cheek series of the skull. The bone forms an ancestra ...

, large elliptical orbital fenestrae (oval eye sockets) and oval external nares (nostrils), a

deltoid Deltoid (delta-shaped) can refer to: * The deltoid muscle, a muscle in the shoulder * Kite (geometry), also known as a deltoid, a type of quadrilateral * A deltoid curve, a three-cusped hypocycloid * A leaf shape * The deltoid tuberosity, a part o ...

dorsal Dorsal (from Latin ''dorsum'' ‘back’) may refer to: * Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism * Dorsal, positioned on top of an aircraft's fuselage The fus ...

profile with a narrow

rostrum Rostrum may refer to: * Any kind of a platform for a speaker: **dais **pulpit ** podium * Rostrum (anatomy), a beak, or anatomical structure resembling a beak, as in the mouthparts of many sucking insects * Rostrum (ship), a form of bow on naval ...

(the snout is tongue-shaped and narrow in top view), quadratojugal protuberances (cheek horns), and caudolaterally directed paroccipital processes (extensions of the rear skull obliquely pointing to behind and sideways). But the two

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 ...

may be distinguished by differences in the length of the maxillary tooth row (40% instead of 26,7% of total skull length), an unfused basipterygoid-pterygoid process in ''Gobisaurus'', the presence of an elongate vomerine premaxillary process in ''Gobisaurus'', and the presence of cranial sculpting in ''Shamosaurus'', but not in ''Gobisaurus''.Vickaryous M.K., Maryańska T., Weishampel D.B., 2004, "Ankylosauria". Chapter 17 in: Weishampel D.B., Dodson P., Osmólska H., editors. ''The Dinosauria''. 2nd ed. Berkeley (CA): University of California Press. p. 363–392 The last difference was denied by Arbour who concluded that the degree of sculpting was roughly the same. ''Shamosaurus'' had a rather flat skull. The upper beak was sharp and obliquely appending to the front. The beak lacked any teeth. The jaw joint was located far behind the level of the eye socket. The

occipital condyle The occipital condyles are undersurface protuberances of the occipital bone in vertebrates, which function in articulation with the superior facets of the Atlas (anatomy), atlas vertebra. The condyles are oval or reniform (kidney-shaped) in shape ...

, and with it the entire head, was obliquely directed to below. A secondary palate was present. The armour of ''Shamosaurus'' contained two cervical halfrings with six segments each, protecting the neck. Also keeled

osteoderm 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 amph ...

s and flat oval scutes were present.

Phylogeny

Tumanova placed ''Shamosaurus'' in the

Ankylosauridae 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 ...

. She also named a Shamosaurinae, a group of basal ankylosaurids. In 2014, Arbour recovered an evolutionary tree in which ''Shamosaurus'' was the

sister species In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...

of ''Gobisaurus''. ''Shamosaurus'' in a

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 ...

simplified from Zheng ''et al''. (2018): In phylogenetic analyses by Xing ''et al''. (2024), ''Shamosaurus'' is recovered as a member of Shamosaurinae or as an ankylosaurid, more derived than ''Gobisaurus''. Below are two simplified cladograms from that study: Topology A: Zheng ''et al''. (2018) dataset + '' Datai'' (14-taxon deletion) Topology B: Raven ''et al''. (2023) dataset + '' Datai'' (34-taxon deletion)

Notes

References

*Matthew K. Vickaryous, Anthony P. Russell, Philip J. Currie, and Xi-Jin Zhao. 2001. A new ankylosaurid (Dinosauria: Ankylosauria) from the Lower Cretaceous of China, with comments on ankylosaurian relationships. Canadian Journal of Earth Sciences/Rev. can. sci. Terre 38(12):1767-1780.

External links

in the Dino Directory
{{Taxonbar, from=Q139221 Ankylosauridae Dinosaur genera Aptian dinosaurs Albian dinosaurs Fossil taxa described in 1983 Dinosaurs of Mongolia