Nemegtosaurus

Nemegtosaurus (meaning 'Reptile from the Nemegt') was a sauropod dinosaur from Late Cretaceous Period of what is now Mongolia. Nemegtosaurus was named after the Nemegt Basin in the Gobi Desert, where the remains — a single skull — were found. The skull resembles diplodocoids in being long and low, with pencil-shaped teeth. However, recent work has shown that Nemegtosaurus is in fact a titanosaur, closely related to animals such as Saltasaurus,[1] Alamosaurus and Rapetosaurus.

Nemegtosaurus
Temporal range: Late Cretaceous, 70 Ma
Opisthocoelicaudia Museum of Evolution in Warsaw 14
Cast of the skull of Nemegtosaurus, on a mounted Opisthocoelicaudia skeleton, Museum of Evolution of Polish Academy of Sciences, Warsaw
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Order: Saurischia
Suborder: Sauropodomorpha
Clade: Sauropoda
Clade: Titanosauria
Clade: Lithostrotia
Family: Nemegtosauridae
Genus: Nemegtosaurus
Nowinski, 1971
Species

N. mongoliensis Nowinski, 1971 (type)
N. pachi Dong, 1977 (nomen dubium)

Synonyms

Discovery and taxonomy

Nemegtosaurus DB
A profile view reconstruction of N. mongoliensis

The skull of Nemegtosaurus comes from the same beds as the titanosaur Opisthocoelicaudia, which is known from a skeleton lacking the neck and skull. Originally, the referral of Nemegtosaurus to Diplodocoidea and Opisthocoelicaudia to Camarasauridae argued that the two represented different species. Both of these genera represent advanced titanosaurians, however, raising the possibility that the two are in fact the same animal.[1] Relocation of the Nemegtosaurus type locality in Central Sayr and discovery of postcrania comparable to those Opisthocoelicauda holotype at the Nemegtosaurus holotype locality has confirmed the possibility that Opisthocoelicauda is a junior synonym. Consequently, Opisthocoelicaudiinae is a junior synonym of Nemegtosauridae.[2]

The type species, Nemegtosaurus mongoliensis, was first described by Nowinski in 1971 on the basis of ZPAL MgD-I/9. A second species, N. pachi, was described by Dong in 1977 on the basis of the teeth IVPP V.4879, but is a nomen dubium.

Biology

Nemegtosaurus is found in the Maastrichtian aged (66-72 Ma) Nemegt Formation, which makes it one of the last sauropods on earth. There, on a lush river delta flowing through the ancient sands of the Gobi Desert, Nemegtosaurus would have coexisted with animals like the ornithomimid Gallimimus, the alvarezsaurid Mononykus, the velociraptorine Adasaurus, and the giant, saber-clawed therizinosaur Therizinosaurus. It also lived alongside the tyrannosaur Tarbosaurus. Its size (estimated at roughly 40 feet long[3]) may have offered an adult some protection against Tarbosaurus, but juveniles would have been vulnerable.

Description

Nemegtosaurus3
A full body restoration of N. mongoliensis

Like other titanosaurs, the teeth are slender pencil-like structures that are ground down at a sharp angle to produce a chisel-like tip. The diet of Nemegtosaurus is unknown, however. There are no plant fossils from the Gobi, but during the Late Cretaceous, flowering plants became increasingly diverse, although in many environments ferns and conifers were still more common. Neither is it clear whether Nemegtosaurus browsed high in the trees or grazed on low-growing plants; related titanosaurs include both long-necked browsing forms like Rapetosaurus and short-necked forms like Bonitasaura.

Comparisons between the scleral rings of Nemegtosaurus and modern birds and reptiles suggest that it may have been cathemeral, active throughout the day at short intervals.[4]

References

  1. ^ a b Benton, Michael J. (2012). Prehistoric Life. Edinburgh, Scotland: Dorling Kindersley. pp. 332–333. ISBN 978-0-7566-9910-9.
  2. ^ Philip J. Currie; Jeffrey A. Wilson; Federico Fanti; Buuvei Mainbayar; Khishigjav Tsogtbaatar (2018). "Rediscovery of the type localities of the Late Cretaceous Mongolian sauropods Nemegtosaurus mongoliensis and Opisthocoelicaudia skarzynskii: Stratigraphic and taxonomic implications". Palaeogeography, Palaeoclimatology, Palaeoecology. in press. doi:10.1016/j.palaeo.2017.10.035.
  3. ^ Holtz Jr., Thomas R. (2007). The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages.
  4. ^ Schmitz, L.; Motani, R. (2011). "Nocturnality in dinosaurs inferred from scleral ring and orbit morphology". Science. 332 (6030): 705–708. Bibcode:2011Sci...332..705S. doi:10.1126/science.1200043. PMID 21493820.
  • Nowinski, A. (1971). Nemegtosaurus mongoliensis n. gen., n. sp. (Sauropoda) from the uppermost Cretaceous of Mongolia. Palaeontologia Polonica 25: 57-81.
  • Wilson, J. (2005). Redescription of the Mongolian sauropod Nemegtosaurus mongoliensis Nowinski (Dinosauria: Saurischia) and comments on Late Cretaceous sauropod diversity. Journal of Systematic Palaeontology. 3. 283 - 318. 10.1017/S1477201905001628.
Diamantinasaurus

Diamantinasaurus is an extinct genus of non-lithostrotian titanosaurian sauropod from Australia that lived during the early Late Cretaceous, about 94 million years ago. The type species of the genus is D. matildae, first described and named in 2009 by Scott Hocknull and colleagues. Meaning "Diamantina lizard", the name is derived from the location of the nearby Diamantina River and the Greek word sauros, "lizard". The specific epithet is from the Australian song Waltzing Matilda, also the locality of the holotype and paratype. The known skeleton includes most of the forelimb, shoulder girdle, pelvis, hindlimb and ribs of the holotype, and one shoulder bone, a radius and some vertebrae of the paratype.

Evolution of dinosaurs

This article gives an outline and examples of dinosaur evolution. For a detailed list of interrelationships see Dinosaur classification.

Dinosaurs evolved within a single lineage of archosaurs 243-233 Ma (million years ago) from the Anisian to the Carnian ages, the latter part of the middle Triassic. Dinosauria is a well-supported clade, present in 98% of bootstraps. It is diagnosed by many features including loss of the postfrontal on the skull and an elongate deltopectoral crest on the humerus.In March 2017, scientists reported a new way of classifying the dinosaur family tree, based on newer and more evidence than available earlier. According to the new classification, the original dinosaurs, arising 200 million years ago, were small, two-footed omnivorous animals with large grasping hands. Descendants (for the non-avian dinosaurs) lasted until 66 million years ago.

Flagellicaudata

Flagellicaudata is a clade of Dinosauria. It belongs to Sauropoda and includes two families, the Dicraeosauridae and the Diplodocidae.

Gravisauria

Gravisauria is a clade of sauropod dinosaurs consisting of some genera, Vulcanodontidae and Eusauropoda.

Jeffrey A. Wilson

Jeffrey A. Wilson also known as "JAW" is a professor of geological sciences and assistant curator at the Museum of Paleontology at the University of Michigan.

His doctoral dissertation was on sauropod evolution and phylogeny, and he has continued this work in cladistic analysis and revision of the group (see e.g. Wilson and Sereno 1994, 1998, Wilson 2005b, and especially Wilson 2002). With Paul Sereno, he defined the clades Macronaria and Somphospondyli (Wilson & Sereno 1998).

Wilson was also involved in the discovery and description of Pabwehshi pakistanensis, the first discovery of decent (diagnostic) Cretaceous crocodylian fossil remains from the Indian subcontinent, in the discovery of Rajasaurus narmadensis, the most completely known theropod dinosaur from India and a member of the family Abelisauridae, description of a number of North African dinosaurs (theropods and sauropods) from Niger, and rediscriptions of the Cretaceous sauropods Titanosaurus colberti (as Isisaurus) and Nemegtosaurus (previously thought to be a diplodocoid, but now recognised as a titanosaur).

His younger brother, Dr. Gregory P. Wilson, studies Mesozoic mammals and is currently an assistant professor in the Department of Biology at the University of Washington, and adjunct curator of vertebrate paleontology at the Burke Museum of Natural History and Culture.

Lithostrotia

Lithostrotia is a clade of derived titanosaur sauropods that lived during the Early Cretaceous and Late Cretaceous. The group was defined by Unchurch et al. in 2004 as the most recent common ancestor of Malawisaurus and Saltasaurus and all the descendants of that ancestor. Lithostrotia is derived from the Ancient Greek lithostros, meaning "inlaid with stones", referring to the fact that many known lithostrotians are preserved with osteoderms. However, osteoderms are not a distinguishing feature of the group, as the two noted by Unchurch et al. include caudal vertebrae with strongly concave front faces (procoely), although the farthest vertebrae are not procoelous.

Lohuecotitan

Lohuecotitan is an extinct genus of titanosaurian sauropod dinosaur which lived during the Late Cretaceous in Spain. The only species known in the genus is Lohuecotitan pandafilandi, described and named in 2016.

Mansourasaurus

Mansourasaurus ("Mansoura lizard") is a genus of herbivorous lithostrotian sauropod dinosaur from the Quseir Formation of Egypt. The type and only species is Mansourasaurus shahinae.

The discovery of Mansourasaurus was considered quite significant by paleontologists, because very few Late Cretaceous sauropod remains had been found in Africa where the rocky strata that preserve remains elsewhere and produce rich fossil beds were typically not found exposed at or near ground level.

Nemegtosauridae

Nemegtosauridae is a family of titanosaurian sauropod dinosaurs based originally on two late Cretaceous Mongolian species known only from their diplodocid-like skulls: Nemegtosaurus and Quaesitosaurus.

Opisthocoelicaudia

Opisthocoelicaudia is a genus of sauropod dinosaur of the Late Cretaceous Period discovered in the Gobi Desert of Mongolia. The type species is Opisthocoelicaudia skarzynskii. A well-preserved skeleton lacking only the head and neck was unearthed in 1965 by Polish and Mongolian scientists, making Opisthocoelicaudia one of the best known sauropods from the Late Cretaceous. Tooth marks on this skeleton indicate that large carnivorous dinosaurs had fed on the carcass and possibly had carried away the now-missing parts. To date, only two additional, much less complete specimens are known, including a part of a shoulder and a fragmentary tail. A relatively small sauropod, Opisthocoelicaudia measured about 11.4 metres (37 ft) in length. Like other sauropods, it would have been characterised by a small head sitting on a very long neck and a barrel shaped trunk carried by four column-like legs. The name Opisthocoelicaudia means "posterior cavity tail", alluding to the unusual, opisthocoel condition of the anterior tail vertebrae that were concave on their posterior sides. This and other skeletal features lead researchers to propose that Opisthocoelicaudia was able to rear on its hindlegs.

Named and described by Polish paleontologist Maria Magdalena Borsuk-Białynicka in 1977, Opisthocoelicaudia was first thought to be a new member of the Camarasauridae, but is currently considered a derived member of the Titanosauria. Its exact relationships within Titanosauria are contentious, but it may have been close to the North American Alamosaurus. All Opisthocoelicaudia fossils stem from the Nemegt Formation. Despite being rich in dinosaur fossils, the only other sauropod from this rock unit is Nemegtosaurus, which is known from a single skull. Since the skull of Opisthocoelicaudia remains unknown, several researchers have suggested that Nemegtosaurus and Opisthocoelicaudia may represent the same species. Sauropod footprints from the Nemegt Formation, which include skin impressions, can probably be referred to either Nemegtosaurus or Opisthocoelicaudia as these are the only known sauropods from this formation.

Postcrania

Postcrania (postcranium, adjective: postcranial) in zoology and vertebrate paleontology refers to all or part of the skeleton apart from the skull. Frequently, fossil remains, e.g. of dinosaurs or other extinct tetrapods, consist of partial or isolated skeletal elements; these are referred to as "postcrania".

Sometimes, there is disagreement over whether the skull and skeleton belong to the same or different animals. One example is the case of a Cretaceous sauropod skull of Nemegtosaurus found in association with the postcranial skeleton Opisthocoelicaudia.

In paleoanthropological studies, reconstruction of relationship between various species/remains is considered to be better supported by cranial characters rather than postcranial characters. However, this assumption is largely untested.

Quaesitosaurus

Quaesitosaurus (meaning "extraordinary lizard") is a genus of nemegtosaurid sauropod found by Kurzanov and Bannikov in 1983. The type species is Quaesitosaurus orientalis. It lived from 85 to 70 million years ago during the Late Cretaceous (Santonian to Campanian ages). Its fossils, consisting solely of a partial skull, were found in the Barun Goyot Formation near Shar Tsav, Mongolia. Long, low and horse-like with frontally located peg-teeth, it is similar enough to the skulls of Diplodocus and its kin to have prompted informed speculation that the missing body was formed like those of diplodocids.

It is possible that Nemegtosaurus, also known from only skull material, is a very close relative of Quaesitosaurus, if not indeed a variation of the same animal.

Saltasaurinae

Saltasaurinae is a subfamily of titanosaurian sauropods known from the late Cretaceous period of South America, India and Madagascar. They are considered to be the most derived of all sauropods.

Savannasaurus

Savannasaurus is a genus of titanosaurian sauropod dinosaur from the Late Cretaceous of Queensland, Australia, containing one species, Savannasaurus elliottorum, named in 2016 by Poropat et al. The only known specimen was originally nicknamed "Wade". The holotype is held on display at the Australian Age of Dinosaurs museum.

Somphospondyli

Somphospondylans are an extinct clade of titanosauriform sauropods that lived throughout the world from the Late Jurassic through the Cretaceous. The group can be defined as "the most inclusive clade that includes Saltasaurus loricatus but excludes Brachiosaurus altithorax". Features found as diagnostic of this clade by Mannion et al. (2013) include the possession of at least 15 cervical vertebrae; a bevelled radius bone end; sacral vertebrae with camellate internal texture; convex posterior articular surfaces of middle to posterior caudal vertebrae; biconvex distal caudal vertebrae; humerus anterolateral corner "squared"; among multiple others.

Subashi Formation

The Subashi Formation (Chinese: 苏巴什组)is a late Cretaceous formation from the Xinjiang Autonomous Region of western China. Initially described by Dong Zhiming in 1977, the formation contains remains of Tarbosaurus which were initially described as a separate taxon Shanshanosaurus huoyanshanensis. Remains of a sauropod, likely Nemegtosaurus, and a hadrosaurid, likely Jaxartosaurus, have also been found.

The formation is located in the Flaming Mountains region of Xinjiang, north of the Turpan Depression. It is not far from Lianmuqin Town of Shanshan County,

and is presumably named after the village of Subashi (42°55′11″N 89°44′36″E), which is located some 15 km to the west of Lianmuqin, in Tuyugou Township (吐峪沟乡).

Tangvayosaurus

Tangvayosaurus (meaning "Tang Vay lizard") is a genus of sauropod dinosaur from the Aptian-Albian age Lower Cretaceous Grès Supérior Formation of Savannakhet, Laos. It was a basal somphospondylan, about 15 m long, and is known from the remains of two or three individuals.

Tapuiasaurus

Tapuiasaurus (meaning "Tapuia lizard") is a genus of titanosaur which lived during the Lower Cretaceous period (Aptian age) in what is now Minas Gerais, Brazil. Its fossils, including a partial skeleton with a nearly complete skull, have been recovered from the Quiricó Formation (Sanfranciscana Basin) at Minas Gerais, eastern Brazil. This genus was named by Hussam Zaher, Diego Pol, Alberto B. Carvalho, Paulo M. Nascimento, Claudio Riccomini, Peter Larson, Rubén Juarez-Valieri, Ricardo Pires-Domingues, Nelson Jorge da Silva Jr. and Diógenes de Almeida Campos in 2011, and the type species is Tapuiasaurus macedoi.Tapuiasaurus was originally assigned to Nemegtosauridae by its original describers, but two subsequent cladistic analyses have recovered it as only distantly related to Nemegtosaurus, with Wilson et al. (2016) recovering the genus outside the Lithostrotia, and Carballido et al. (2017) recovering it as closely related to the Gondwanan lithostrotians Isisaurus and Rapetosaurus.

Tarbosaurus

Tarbosaurus ( TAR-bə-SAWR-əs; meaning "alarming lizard") is a genus of tyrannosaurid theropod dinosaur that flourished in Asia about 70 million years ago, at the end of the Late Cretaceous Period. Fossils have been recovered in Mongolia, with more fragmentary remains found further afield in parts of China.

Although many species have been named, modern paleontologists recognize only one, T. bataar, as valid. Some experts see this species as an Asian representative of the North American genus Tyrannosaurus; this would make the genus Tarbosaurus redundant. Tarbosaurus and Tyrannosaurus, if not synonymous, are considered to be at least closely related genera. Alioramus, also from Mongolia, is thought by some authorities to be the closest relative of Tarbosaurus.

Like most known tyrannosaurids, Tarbosaurus was a large bipedal predator, weighing up to five tonnes and equipped with about sixty large teeth. It had a unique locking mechanism in its lower jaw and the smallest forelimbs relative to body size of all tyrannosaurids, renowned for their disproportionately tiny, two-fingered forelimbs.

Tarbosaurus lived in a humid floodplain criss-crossed by river channels. In this environment, it was an apex predator, probably preying on other large dinosaurs like the hadrosaur Saurolophus or the sauropod Nemegtosaurus. Tarbosaurus is represented by dozens of fossil specimens, including several complete skulls and skeletons. These remains have allowed scientific studies focusing on its phylogeny, skull mechanics, and brain structure.

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