Nemegtosauridae
Encyclopedia
Nemegtosauridae is a family of probably titanosaur
ian sauropod dinosaurs based originally on two late Cretaceous
Mongolian species known only from their diplodocid-like skulls: Nemegtosaurus
and Quaesitosaurus
. Authorities disagree as to the relationship of these two genera with other sauropods, and indeed whether they even constitute a valid family. More recently, additional sauropods have been added to this group, and cladistic methodology has been used to shed further light on the evolutionary relationships of these animals.
, as they resemble the skull of Dicraeosaurus
, although differing in certain details. Although the skull of Nemegtosaurus was found in the same formation as the headless skeleton of Opisthocoelicaudia
, McIntosh rejects the possibility that they belong to the same animal, as Nemegtosaurus is diplodocid-like, but Opisthocoelicaudia camarasaur-like.
Upchurch 1995 placed the two genera
in their own family, without giving a cladistic definition. However, the name first appeared in print a few weeks earlier in a paper by Barrett and Upchurch.
Wilson in 2002 referred the two genera to the family Nemegtosauridae, and on the basis of cladistic analysis
, transferred them from the Diplodocoidea
to the Titanosauria
Apesteguia (2004), in a paper describing a new Patagonia
n sauropod, Bonitasaura salgadoi
, may have been the first to properly define the taxon, although without the use of cladistic analysis: the stemclade
consisting of all titanosaurs more closely related to Nemegtosaurus than to Saltasaurus
. He argued for a close relationship between Nemegtosaurus, Quaesitosaurus, Rapetosaurus, and Bonitasaura and referred to the previous phylogenetic analysis and use of Nemegtosauridae by Wilson (2002).
Upchurch et al. 2004 returned the Nemegtosauridae to the Diplodocoidea, and defined the former as the stem clade consisting of all Diplodocoidea closer to Nemegtosaurus than to Diplodocus. The only known species were Nemegtosaurus itself and Queasitosaurus.
Curry Rogers 2005, in one of the most complete cladistic analysis of the Titanosauria to date, returns both Nemegtosaurus and Quaesitosaurus to the titanosaurs, but rejects the validity of both the family Nemegtosauridae and the clade concepts given under that name. Quaesitosaurus is placed in the Saltasaurinae and Nemegtosaurus in a new, unnamed "Rapetosaurus
clade" (which, under ICZN rules, would, if named, be termed subfamily Nemegtosaurinae or tribe Nemegtosaurini, depending on its position). She places Opisthocoelicaudia in a separate clade, the Opisthocoelicaudiinae
. All three clades are included in the Saltasauridae (= Titanosauridae).
Unaware of Apesteguia's work, Wilson (2005) proposed a definition identical to his and further clarified the anatomy and relationships of the central genus Nemegtosaurus. He thus also defines the Nemegtosauridae as a stem-based
clade that includes all titanosaurs more closely related to Nemegtosaurus than to Saltasaurus
. He also suggests that Opisthocoelicaudia may eventually be shown to be a junior synonym of Nemegtosaurus.
below follows Zaher et al. (2011).
Titanosaur
Titanosaurs were a diverse group of sauropod dinosaurs, which included Saltasaurus and Isisaurus. It includes some of the heaviest creatures ever to walk the earth, such as Argentinosaurus and Paralititan — which some believe have weighed up to 100 tonnes...
ian sauropod dinosaurs based originally on two late Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
Mongolian species known only from their diplodocid-like skulls: Nemegtosaurus
Nemegtosaurus
Nemegtosaurus was a sauropod dinosaur from Late Cretaceous Period of what is now Mongolia. It was named after the Nemegt Basin in the Gobi Desert, where the remains — a single skull — were found...
and Quaesitosaurus
Quaesitosaurus
Quaesitosaurus is a genus of titanosaurian 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...
. Authorities disagree as to the relationship of these two genera with other sauropods, and indeed whether they even constitute a valid family. More recently, additional sauropods have been added to this group, and cladistic methodology has been used to shed further light on the evolutionary relationships of these animals.
History of classification
McIntosh 1990 included both these animals in the family Diplodocidae, subfamily DicraeosaurinaeDicraeosauridae
Dicraeosauridae is a family of sauropod dinosaurs known from the Late Jurassic and Early Cretaceous of Africa and South America. Currently only three genera are recognised; the Jurassic South American genus Brachytrachelopan, the Jurassic African Dicraeosaurus and the South American Early...
, as they resemble the skull of Dicraeosaurus
Dicraeosaurus
Dicraeosaurus is a genus of small diplodocoid sauropod dinosaur. It was named for the spines on the back of the neck. The first fossil was described by paleontologist Werner Janensch in 1914.Unlike most diplodocoids, Dicraeosaurus had a large head with a relatively short and wide neck...
, although differing in certain details. Although the skull of Nemegtosaurus was found in the same formation as the headless skeleton of Opisthocoelicaudia
Opisthocoelicaudia
Opisthocoelicaudia was 12-metre-long sauropod dinosaur of the Late Cretaceous Period discovered in Mongolia in 1965 by Polish and Mongolian scientists in what is now the Gobi Desert...
, McIntosh rejects the possibility that they belong to the same animal, as Nemegtosaurus is diplodocid-like, but Opisthocoelicaudia camarasaur-like.
Upchurch 1995 placed the two genera
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
in their own family, without giving a cladistic definition. However, the name first appeared in print a few weeks earlier in a paper by Barrett and Upchurch.
Wilson in 2002 referred the two genera to the family Nemegtosauridae, and on the basis of cladistic analysis
Cladistics
Cladistics is a method of classifying species of organisms into groups called clades, which consist of an ancestor organism and all its descendants . For example, birds, dinosaurs, crocodiles, and all descendants of their most recent common ancestor form a clade...
, transferred them from the Diplodocoidea
Diplodocoidea
Diplodocoidea was a superfamily of sauropod dinosaurs, which included some of the longest animals of all time, including slender giants like Supersaurus, Diplodocus, Apatosaurus, and Amphicoelias...
to the Titanosauria
Apesteguia (2004), in a paper describing a new Patagonia
Patagonia
Patagonia is a region located in Argentina and Chile, integrating the southernmost section of the Andes mountains to the southwest towards the Pacific ocean and from the east of the cordillera to the valleys it follows south through Colorado River towards Carmen de Patagones in the Atlantic Ocean...
n sauropod, Bonitasaura salgadoi
Bonitasaura
Bonitasaura is a titanosaurian dinosaur hailing from uppermost layers of the Late Cretaceous Bajo de la Carpa Formation, Neuquen Group, located in Río Negro Province, Northwestern Patagonia, Argentina...
, may have been the first to properly define the taxon, although without the use of cladistic analysis: the stemclade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
consisting of all titanosaurs more closely related to Nemegtosaurus than to Saltasaurus
Saltasaurus
Saltasaurus is a genus of titanosaurid sauropod dinosaur of the Late Cretaceous Period. Relatively small among sauropods, though still massive by the standards of modern creatures, Saltasaurus was characterized by a diplodocid-like head...
. He argued for a close relationship between Nemegtosaurus, Quaesitosaurus, Rapetosaurus, and Bonitasaura and referred to the previous phylogenetic analysis and use of Nemegtosauridae by Wilson (2002).
Upchurch et al. 2004 returned the Nemegtosauridae to the Diplodocoidea, and defined the former as the stem clade consisting of all Diplodocoidea closer to Nemegtosaurus than to Diplodocus. The only known species were Nemegtosaurus itself and Queasitosaurus.
Curry Rogers 2005, in one of the most complete cladistic analysis of the Titanosauria to date, returns both Nemegtosaurus and Quaesitosaurus to the titanosaurs, but rejects the validity of both the family Nemegtosauridae and the clade concepts given under that name. Quaesitosaurus is placed in the Saltasaurinae and Nemegtosaurus in a new, unnamed "Rapetosaurus
Rapetosaurus
Rapetosaurus is a genus of sauropod dinosaur that lived in Madagascar from 70 to 65 million years ago, at the end of the Cretaceous Period. Only one species Rapetosaurus is a genus of sauropod dinosaur that lived in Madagascar from 70 to 65 million years ago, at the end of the Cretaceous Period....
clade" (which, under ICZN rules, would, if named, be termed subfamily Nemegtosaurinae or tribe Nemegtosaurini, depending on its position). She places Opisthocoelicaudia in a separate clade, the Opisthocoelicaudiinae
Opisthocoelicaudiinae
The Opisthocoelicaudiinae is a clade of titanosaurian dinosaurs from the Late Cretaceous, ranked as a subfamily. Opisthocoelicaudiines are known from China, Mongolia, and the United States . Three genera have been assigned to Opisthocoelicaudiinae: Alamosaurus, Borealosaurus, and...
. All three clades are included in the Saltasauridae (= Titanosauridae).
Unaware of Apesteguia's work, Wilson (2005) proposed a definition identical to his and further clarified the anatomy and relationships of the central genus Nemegtosaurus. He thus also defines the Nemegtosauridae as a stem-based
PhyloCode
The International Code of Phylogenetic Nomenclature, known as the PhyloCode for short, is a developing draft for a formal set of rules governing phylogenetic nomenclature...
clade that includes all titanosaurs more closely related to Nemegtosaurus than to Saltasaurus
Saltasaurus
Saltasaurus is a genus of titanosaurid sauropod dinosaur of the Late Cretaceous Period. Relatively small among sauropods, though still massive by the standards of modern creatures, Saltasaurus was characterized by a diplodocid-like head...
. He also suggests that Opisthocoelicaudia may eventually be shown to be a junior synonym of Nemegtosaurus.
Phylogeny
The cladogramCladogram
A cladogram is a diagram used in cladistics which shows ancestral relations between organisms, to represent the evolutionary tree of life. Although traditionally such cladograms were generated largely on the basis of morphological characters, DNA and RNA sequencing data and computational...
below follows Zaher et al. (2011).