Shamosaurus

Shamosaurus is an extinct genus of herbivorous basal ankylosaurid ankylosaur from Early Cretaceous (Aptian to Albian stage) deposits of Höövör, Mongolia.

Shamosaurus
Temporal range: Early Cretaceous, Aptian–Albian
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Order: Ornithischia
Family: Ankylosauridae
Subfamily: Shamosaurinae
Tumanova, 1983
Genus: Shamosaurus
Tumanova, 1983
Species:
S. scutatus
Binomial name
Shamosaurus scutatus
Tumanova, 1983

Discovery and naming

In 1977, a Soviet-Mongolian expedition discovered the skeleton of an unknown ankylosaurian at the Chamrin-Us site in Dornogovi Province. This was the first discovery of an ankylosaur in the Lower Cretaceous of Mongolia.[1]

In 1983, Tatyana Tumanova named and described the type species Shamosaurus scutatus. The generic name is derived from Mandarin sha mo, "sand desert", the Chinese name for the Gobi. The specific name means "protected by a shield" in Latin, a reference to the body armour.[1]

Shamosaurus is known from the holotype PIN N 3779/2, collected from the Dzunbain Formation, equivalent to the Khukhtekskaya Formation and dating from the Aptian-Albian, about 115 million years old. It consists of a complete skull, lower jaws and partial postcranial skeleton with armor. Only the skull was described in 1983.[1] 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. The holotype skull is exhibited there, together with two cervical halfrings.[2]

Description

Shamosaurus was a medium-sized ankylosaurian. In 2010, Gregory S. Paul estimated its body length at five metres, its weight at two tonnes.[3]

In 2014, Victoria Megan Arbour gave a revised list of distinguishing traits. The osteoderms 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.[2]

Shamosaurus scutatus shares many cranial similarities with Gobisaurus domoculus, including a rounded squamosal, large elliptical orbital fenestrae (oval eye sockets) and oval external nares (nostrils), a deltoid dorsal profile with a narrow rostrum (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 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.[4] The last difference was denied by Arbour who concluded that the degree of sculpting was roughly the same.[2]

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, and with it the entire head, was obliquely directed to below. A secondary palate was present.[1]

The armour of Shamosaurus contained two cervical halfrings with six segments each, protecting the neck. Also keeled osteoderms and flat oval scutes were present.[1]

Phylogeny

Tumanova placed Shamosaurus in the Ankylosauridae.[1] She also named a Shamosaurinae, a group of basal ankylosaurids. In 2014, Arbour recovered an evolutionary tree in which Shamosaurus was the sister species of Gobisaurus.[2]

See also

Notes

  1. ^ a b c d e f 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
  2. ^ a b c d Arbour, Victoria Megan, 2014. Systematics, evolution, and biogeography of the ankylosaurid dinosaurs. Ph.D thesis, University of Alberta
  3. ^ Paul, G.S., 2010, The Princeton Field Guide to Dinosaurs, Princeton University Press p. 230
  4. ^ 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

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

Acantholipan

Acantholipan is a genus of herbivorous nodosaurid dinosaur from Mexico from the early Santonian age of the Late Cretaceous. It includes one species, Acantholipan gonzalezi.

Ankylosauridae

Ankylosauridae () is a family of armored dinosaurs within Ankylosauria, and is the sister group to Nodosauridae. Ankylosaurids appeared 122 million years ago and went extinct 66 million years ago during the Cretaceous–Paleogene extinction event. These animals were mainly herbivorous and were obligate quadrupeds, with leaf-shaped teeth and robust, scute-covered bodies. Ankylosaurids possess a distinctly domed and short snout, wedge-shaped osteoderms on their skull, scutes along their torso, and a tail club.Ankylosauridae is exclusively known from the northern hemisphere, with specimens found in western North America, Europe, and East Asia. The first discoveries within this family were of the genus Ankylosaurus, by Peter Kaiser and Barnum Brown in Montana in 1906. Brown went on to name Ankylosauridae and the subfamily Ankylosaurinae in 1908.

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, Pinacosaurus, Euoplocephalus, and Saichania.

Bienosaurus

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Bissektipelta

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Cedarpelta

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Chuanqilong

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Crichtonpelta

Crichtonpelta is a genus of extinct herbivorous ankylosaurid dinosaur from the Cretaceous of China.In 2007, Lü Junchang, Ji Qiang, Gao Yubo and Li Zhixin named and described a second species of Crichtonsaurus: Crichtonsaurus benxiensis. The specific name refers to the Benxi Geological Museum.The holotype, BXGMV0012, is a skull found near Beipiao in a layer of the Sunjiawan Formation probably dating from the Albian. Specimen BXGMV0012-1, a skeleton lacking the skull, discovered in the same quarry as the holotype, was referred to the species. Furthermore, a skeleton with skull, displayed by the Sihetun Fossil Museum as a Crichtonsaurus bohlini specimen, was in 2014 referred to Crichtonpelta. In 2017, a fourth specimen was described, from the same quarry as the holotype, G20090034, consisting of a skull lacking the front snout.In 2014, Victoria Arbour concluded that Crichtonsaurus were a nomen dubium. Therefore, she named a separate genus for its second species: Crichtonpelta. The generic name combines a reference to Michael Crichton, the author of Jurassic Park, with a Greek πέλτη, peltè, "small shield". At the time this was an invalid nomen ex dissertatione. However, in 2015, Crichtonpelta was validly named by Arbour and Philip John Currie. The type species is Crichtonsaurus benxiensis; the combinatio nova is Crichtonpelta benxiensis. There was a possibility that, though Crichtonsaurus bohlini was a nomen dubium, its fossil material in fact belonged to Crichtonpelta. Arbour however, noted clear differences in the scapula and humerus between BXGMV0012-1 and LPM 101, a specimen previously referred to Crichtonsaurus bohlini: the scapula of the former has a tab-like acromion and its humerus a much longer deltopectoral crest.Arbour established several distinguishing traits. One of these was an autapomorphy, unique derived trait: the apex of the (quadrato)jugal, or cheek, horn, is pointing upwards. Also a unique combination of in themselves not unique traits is present. The upper snout armour forms an amorphous mass, not clearly separated into distinctive tiles. The jugal bone is deeper than that of Pinacosaurus. The skull roof is not notched at the lacrimal bone as in Pinacosaurus grangeri. The squamosal horns are shorter than those of Pinacosaurus mephistocephalus. However, these horns are longer and more pointed than those of Gobisaurus or Shamosaurus. The point of the cheek horn is located on the rear edge. The transverse crest on the top of the rear skull has two points.The holotype of Crichtonpelta is somewhat larger than Crichtonsaurus, itself about three to four metres long. It is uncertain whether Crichtonpelta already possessed a tail club.Crichtonpelta was, within the Ankylosauridae, placed in the Ankylosaurinae, in a basal position. If correct, this makes it the oldest known ankylosaurine.

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Gobisaurus

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Invictarx

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Mongolostegus

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Nodosaurus

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Sauroplites

Sauroplites (meaning "saurian hoplite") is a genus of herbivorous ankylosaurian dinosaur from the Early Cretaceous of China.

In 1930, the Swedish paleontologist Anders Birger Bohlin during the Swedish-Chinese expeditions of Sven Hedin discovered an ankylosaurian fossil near Tebch in Inner Mongolia.The type species Sauroplites scutiger was named and described by Bohlin in 1953. The generic name is derived from Greek sauros or saura, "lizard", and hoplites, "hoplite, armed foot soldier". The specific name is new Latin for "shield bearer", in reference to the body armour.The specimens were not given an inventory number and are today lost, though some casts are present in the American Museum of Natural History as specimen AMNH 2074. They were found in a layer of the Zhidan Group, probably dating from the Barremian to Aptian stages. The carcass had been deposited on its back and the bones had been eroded away, apart from some ribs and perhaps a piece of an ischium, leaving parts of the body armour in a largely articulated position.At first generally accepted as valid, even though a diagnosis had originally not been provided, Sauroplites was later often considered a nomen dubium because it is based on fragmentary material. Some believed it might actually be a specimen of another ankylosaur, Shamosaurus. However, in 2014 Victoria Megan Arbour discovered a clear unique trait, autapomorphy: the sacral or pelvic shield shows rosettes with a large central osteoderm surrounded by a single ring of smaller scutes. Other species have multiple or irregular rings. She concluded that Sauroplites was a valid taxon.The large central osteoderms of the rosettes are rather flat and have a diameter of ten centimetres. More to the front oval osteoderms, with an asymmetric low keel, cover the back, with a length of up to forty centimetres. Thirty centimetre osteoderms cover the sides.Bohlin placed Sauroplites in the Ankylosauridae. However, Arbour considered it possible that it was a member of the Nodosauridae in view of the possession of a sacral shield consisting of fused rosettes which is unknown with unequivocal ankylosaurids, even though nodosaurid remains from Asia are rare and contentious. In a cladistic analysis she performed, Sauroplites was recovered as a nodosaurid.

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Tatisaurus

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Texasetes

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Tianzhenosaurus

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Vickaryous et al. (2004) placed Tianzhenosaurus within the Ankylosauridae, nested as the sister group to Pinacosaurus. Some authors have suggested that Tianzhenosaurus is actually a junior synonym of Saichania chulsanensis.

Tsagantegia

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The holotype specimen (GI SPS N 700/17), a complete skull, was recovered from the Bayan Shireh Formation (Cenomanian-Santonian), at the Tsagan-Teg ("White Mountain") locality, Dzun-Bayan, in the southeastern Gobi Desert, Mongolia. The genus is monotypic, including only the type species, T. longicranialis.

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