Nemegtosauridae
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Nemegtosauridae is a
family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...
of
titanosaur Titanosaurs (or titanosaurians; members of the group Titanosauria) were a diverse group of sauropod dinosaurs, including genera from all seven continents. The titanosaurs were the last surviving group of long-necked sauropods, with taxa still thr ...
ian sauropod dinosaurs based on their diplodocid-like
skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, th ...
s. Only three species are known: ''
Nemegtosaurus ''Nemegtosaurus'' (meaning 'Reptile from the Nemegt') was a sauropod dinosaur from the 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. ...
'', '' Quaesitosaurus'' and possibly '' Tapuiasaurus'', each from the
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...
.


History of classification

Due to the diplodocid-like nature of the taxa placed in Nemegtosauridae, the systematic position of this family in Sauropoda was disputed until recently. McIntosh (1990) included both these animals in the family
Diplodocidae Diplodocids, or members of the family Diplodocidae ("double beams"), are a group of sauropod dinosaurs. The family includes some of the longest creatures ever to walk the Earth, including ''Diplodocus'' and ''Supersaurus'', some of which may have ...
, subfamily Dicraeosaurinae, as they resemble the skull of ''
Dicraeosaurus ''Dicraeosaurus'' (Gr. , ' "bifurcated, double-headed" + Gr. , ' "lizard") is a genus of diplodocoid sauropod dinosaur that lived in what is now Lindi Region, Tanzania during the late Jurassic period. The genus was named for the neural spines on ...
'', although differing in certain details. Although the skull of ''Nemegtosaurus'' was found in the same formation as the headless skeleton of ''
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 wa ...
'', McIntosh (1990) kept ''Nemegtosaurus'' in Diplodocoidea while keeping ''Opisthocoelicaudia'' separate from the former, a position reiterated by Upchurch (1995, 1999), and Upchurch et al. (2004). A
cladistic analysis Cladistics (; ) is an approach to biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically shared derived chara ...
published in 2002 transferred ''Nemegtosaurus'' and ''Opisthocoelicaudia'' from Diplodocoidea to
Titanosauria Titanosaurs (or titanosaurians; members of the group Titanosauria) were a diverse group of sauropod dinosaurs, including genera from all seven continents. The titanosaurs were the last surviving group of long-necked sauropods, with taxa still thr ...
. Apesteguia (2004), in a paper describing a new
Patagonia Patagonia () refers to a geographical region that encompasses the southern end of South America, governed by Argentina and Chile. The region comprises the southern section of the Andes Mountains with lakes, fjords, temperate rainforests, and g ...
n sauropod, '' Bonitasaura salgadoi'', may have been the first to properly define the taxon, although without the use of cladistic analysis: the stem clade consisting of all titanosaurs more closely related to ''Nemegtosaurus'' than to ''
Saltasaurus ''Saltasaurus'' (which means "lizard from Salta") is a genus of saltasaurid dinosaur of the Late Cretaceous period of Argentina. Small among sauropods, though still heavy by the standards of modern creatures, ''Saltasaurus'' was characterized by ...
''. 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). In his redescription of the ''
Nemegtosaurus ''Nemegtosaurus'' (meaning 'Reptile from the Nemegt') was a sauropod dinosaur from the 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. ...
'' holotype, Wilson (2005) elaborated on the titanosaurian nature of ''Nemegtosaurus'', defining Nemegtosauridae as a stem-based clade that includes all titanosaurs more closely related to ''Nemegtosaurus'' than to ''
Saltasaurus ''Saltasaurus'' (which means "lizard from Salta") is a genus of saltasaurid dinosaur of the Late Cretaceous period of Argentina. Small among sauropods, though still heavy by the standards of modern creatures, ''Saltasaurus'' was characterized by ...
''. He also suggested that ''Opisthocoelicaudia'' may eventually be shown to be a junior synonym of ''Nemegtosaurus''. For her part,
Kristina Curry Rogers Kristina "Kristi" Curry Rogers (born June 20, 1974) is an American vertebrate paleontologist and a professor in Biology and Geology at Macalester College. Her research focuses on questions of dinosaur paleobiology, bone histology, growth, and e ...
(see also Cuury Rogers and Forster
001 001, O01, or OO1 may refer to: *1 (number), a number, a numeral *001, fictional British agent, see 00 Agent *001, former emergency telephone number for the Norwegian fire brigade (until 1986) *AM-RB 001, the code-name for the Aston Martin Valkyrie ...
agreed with Wilson that both ''Nemegtosaurus'' and ''Quaesitosaurus'' were titanosaurs rather than diplodocoids, but rejected the validity of Nemegtosauridae and the clade concepts given under that name. ''Quaesitosaurus'' was placed in the Saltasaurinae and ''Nemegtosaurus'' in a new, unnamed "''
Rapetosaurus ''Rapetosaurus'' ( ) is a genus of titanosaurian sauropod dinosaur that lived in Madagascar from 70 to 66 million years ago, at the end of the Cretaceous Period. Only one species, ''Rapetosaurus krausei'', has been identified. Like other sauropo ...
'' clade" (which, under ICZN rules, would, if named, be termed subfamily Nemegtosaurinae or tribe Nemegtosaurini, depending on its position). ''Opisthocoelicaudia'' was placed in a separate clade, the Opisthocoelicaudiinae. All three clades are included in the Saltasauridae (= Titanosauridae). In a paper discussing new anatomical data on the skull of ''Tapuiasaurus'', Wilson and his colleagues cast doubt on the monophyly of Nemegtosauridae, judging from a rescoring of the Zaher et al. 2011 cladistic analysis regarding cranial characters. ''Tapuiasaurus'' was recovered as basal to Lithostrotia, rendering its position within Nemegtosauridae questionable. A 2014 cladistic analysis gleaning new anatomical data from ''Diamantinasaurus'' also rendered Nemegtosauridae paraphyletic, with ''
Rapetosaurus ''Rapetosaurus'' ( ) is a genus of titanosaurian sauropod dinosaur that lived in Madagascar from 70 to 66 million years ago, at the end of the Cretaceous Period. Only one species, ''Rapetosaurus krausei'', has been identified. Like other sauropo ...
'' falling out as a member of Saltasauridae closer to '' Isisaurus'' than to ''Nemegtosaurus''. The cladistic analysis of ''
Patagotitan ''Patagotitan'' is a genus of titanosaurian sauropod dinosaur from the Cerro Barcino Formation in Chubut Province, Patagonia, Argentina. The genus contains a single species known from multiple individuals: ''Patagotitan mayorum'', first announc ...
'' recovered ''Tapuiasaurus'' as the sister taxon of ''Rapetosaurus'' and ''Isisaurus'' but not ''Nemegtosaurus''. Nemegtosauridae was retained as a potentially useful clade of titanosaurs by Carballido and colleagues in 2022, who noted that it was either resolved as a small clade of titanosaurs, or an extensive group of taxa closer to ''Nemegtosaurus'' than ''Saltasaurus''. Further work on the discovered postcrania was required to resolve the relationships of ''Nemegtosaurus'' and ''Opisthocoelicaudia'', but it was preliminarily retained as a clade of saltasauroid that may end up as a synonym of Opisthocoelicaudiinae or even
Lirainosaurinae Lirainosaurinae is a subfamily of lithostrotian titanosaur sauropods from the Late Cretaceous of France, Spain, and Romania. Systematics Lirainosaurinae was defined by Díez Díaz ''et al.'' (2018) as comprising "'' Lirainosaurus'', ''Ampelosaur ...
.


Phylogeny

The
cladogram A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to ...
below follows Zaher ''et al.'' (2011).


References

{{Taxonbar, from=Q134474 Titanosaurs Lithostrotians Prehistoric dinosaur families