''Bagaraatan'' (/'ba-ɣa-raa-tan/ meaning 'small' ''baɣa'' + 'carnivorous animal, beast of prey' ''araatan'' in Mongolian) is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

theropod Theropoda (; from ancient Greek , (''therion'') "wild beast"; , (''pous, podos'') "foot"">wiktionary:ποδός"> (''pous, podos'') "foot" is one of the three major groups (clades) of dinosaurs, alongside Ornithischia and Sauropodom ...

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...

from the Late

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

period. Its fossils were found in the Nemegt Formation of

Mongolia Mongolia is a landlocked country in East Asia, bordered by Russia to the north and China to the south and southeast. It covers an area of , with a population of 3.5 million, making it the world's List of countries and dependencies by po ...

. ''Bagaraatan'' may have been around 3 to 4 metres (9.8 to 13 ft) in length.

History

The

type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...

, ''B. ostromi'', was described by Halszka Osmólska in 1996. Initially, the post-cranial ( ZPAL MgD-I/108) skeleton had been described as "bird-like", while the skull was noted to exhibit features of several different theropod groups. The material that warranted this conclusion was later found to be a chimaera of two non-avian dinosaurs, with some of the post-crania (hand bones, left femur, tibiotarsus, and rib) being referred to an indeterminate caenagnathid, possibly '' Elmisaurus''. The material that is considered the holotype, which includes the mandible, axial skeleton, pelvis, and one pedal phalanx, likely indicates that ''Bagaraatan'' is an indeterminate tyrannosaurid. Similarities between the material and young specimens of ''

Tyrannosaurus ''Tyrannosaurus'' () is a genus of large theropod dinosaur. The type species ''Tyrannosaurus rex'' ( meaning 'king' in Latin), often shortened to ''T. rex'' or colloquially t-rex, is one of the best represented theropods. It lived througho ...

'' and '' Tarbosaurus'' indicate that the holotype represents a juvenile tyrannosaurid, one of the smallest currently known.

Classification

Holtz classified ''Bagaraatan'' as a basal tyrannosauroid, Coria identified it as a

troodontid Troodontidae is a clade of bird-like theropod dinosaurs from the Late Jurassic to Late Cretaceous. During most of the 20th century, troodontid fossils were few and incomplete and they have therefore been allied, at various times, with many dinos ...

, and Rauhut placed it in

Maniraptora Maniraptora is a clade of coelurosaurian dinosaurs which includes the birds and the non-avian dinosaurs that were more closely related to them than to ''Ornithomimus velox''. It contains the major subgroups Avialae, Dromaeosauridae, Troodontidae, ...

.O. W. M. Rauhut (2003). The interrelationships and evolution of basal theropod dinosaurs. ''Special Papers in Palaeontology'' 69: 1-213. Mark Loewen ''et al.'' placed it in basal Tyrannosauroidea, agreeing with the placement by Holtz. Below is the

cladogram A cladogram (from Greek language, Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an Phylogenetic tree, evolutionary tree because it does not s ...

by Loewen ''et al.'' in 2013. In their 2024 reassessment of ''Bagaraatan'', Słowiak, Brusatte & Szczygielski determined that the initial material referred to ''Bagaraatan'' is chimaeric. They suggested that the material recognized as the holotype can more confidently be identified as a member of the

Tyrannosauridae Tyrannosauridae (or tyrannosaurids, meaning "tyrant lizards") is a family of coelurosaurian theropod dinosaurs that comprises two subfamilies containing up to fifteen genera, including the eponymous ''Tyrannosaurus''. The exact number of genera ...

or a closely related tyrannosauroid. When tested in a

phylogenetic analysis In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical data ...

, ''Bagaraatan'' was recovered in a polytomy with derived tyrannosauroids within the Tyrannosauridae. However, they caution that its exact phylogenetic position remains uncertain since juvenile specimens tend to be recovered in more basal positions than adults of the same species. Their results are shown in the cladogram below:

References

Sources

* Osmolska, H. (1996). "An unusual theropod dinosaur from the Late Cretaceous Nemegt Formation of Mongolia". ''Acta Palaeontologica Polonica'' 41; 1-3

External links

Dinosaur Mailing List entry which discusses the genus
{{Taxonbar, from=Q134285 Tyrannosauroidea Dinosaur genera Maastrichtian dinosaurs Nemegt Formation Fossil taxa described in 1996 Taxa named by Halszka Osmólska Dinosaurs of Mongolia