Shamosaurus

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Shamosaurus
Temporal range: Early Cretaceous, Aptian–Albian
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: †Ornithischia
Clade: †Thyreophora
Clade: †Ankylosauria
Family: †Ankylosauridae
Subfamily: †
Shamosaurinae

Tumanova, 1983
Genus: †Shamosaurus
Tumanova, 1983
Species:
†S. scutatus
Binomial name
†Shamosaurus scutatus
Tumanova, 1983

Shamosaurus is an

ankylosaur from Early Cretaceous (Aptian to Albian stage) deposits of Höövör, Mongolia
.

Discovery and naming

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

Lower Cretaceous of Mongolia.[1]

In

Gobi. The specific name means "protected by a shield" in Latin, a reference to the body armour.[1]

Shamosaurus is known from 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 5 metres (16 ft), its weight at 2 tonnes (2.2 short tons).[3] In 2012 Holtz gave a higher estimation of 7 meters (23 ft).[4]

In 2014,

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

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.[5] 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

sister species of Gobisaurus.[2]

Shamosaurus in a cladogram simplified from Zheng et al. (2018):[6]

Ankylosauridae

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:[7]

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. ^ Holtz Jr., Tomas R. (2012). "Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages" (PDF).
  5. ^ 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
  6. PMID 29487376
    .
  7. ISSN 2292-1389
    .

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
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