The "Gurlin Tsav" skull is a currently unnamed

carnivorous A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other ...

metatheria Metatheria is a mammalian clade that includes all mammals more closely related to marsupials than to placentals. First proposed by Thomas Henry Huxley in 1880, it is a more inclusive group than the marsupials; it contains all marsupials as we ...

n fossil from the

Nemegt Formation The Nemegt Formation (also known as Nemegtskaya Svita) is a geological formation in the Gobi Desert of Mongolia, dating to the Late Cretaceous. The formation consists of river channel sediments and contains fossils of fish, turtles, crocodilians ...

Mongolia Mongolia; Mongolian script: , , ; lit. "Mongol Nation" or "State of Mongolia" () is a landlocked country in East Asia, bordered by Russia to the north and China to the south. It covers an area of , with a population of just 3.3 millio ...

. Composed of a single semi-complete skull, this specimen is notable in regards to the evolution and systematics of Metatheria as a whole, and thus nigh-omnipresent in phylogenetic analyses of this group.S. Bi, X. Jin, S. Li and T. Du. 2015. A new Cretaceous metatherian mammal from Henan, China. PeerJ 3:e896Guillermo W. Rougier; Brian M. Davis; Michael J. Novacek (2015). "A deltatheroidan mammal from the Upper Cretaceous Baynshiree Formation, eastern Mongolia". Cretaceous Research. 52, Part A: 167–177. doi:10.1016/j.cretres.2014.09.009.

Fossil location

The Gurlin Tsav skull, as the informal name indicates, comes from the Gurlin Tsav track in the

. This area represents fluvial deposits, and also heralds a few dinosaur specimens, such as a ''

Saurolophus ''Saurolophus'' (; meaning "lizard crest") is a genus of large hadrosaurid dinosaur from the Late Cretaceous period of Asia and North America, that lived in what is now the Horseshoe Canyon and Nemegt formations about 70 million to 68 millio ...

'' skeleton.

Classification

The specimen was originally referred to

Deltatheroida Deltatheroida is an extinct group of basal metatherians that were distantly related to modern marsupials. The majority of known members of the group lived in the Cretaceous; one species, '' Gurbanodelta kara'', is known from the late Paleocene ( ...

, a clade of carnivorous metatherians rather common in the Cretaceous of

Asia Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an ...

Zofia Kielan-Jaworowska Zofia Kielan-Jaworowska (25 April 1925 – 13 March 2015) was a Polish paleobiologist. In the mid-1960s, she led a series of Polish-Mongolian paleontological expeditions to the Gobi Desert. She was the first woman to serve on the executive commit ...

, Lev A. Nessov, On the metatherian nature of the Deltatheroida, a sister group of the Marsupialia, First published: January 1990Full publication history DOI: 10.1111/j.1502-3931.1990.tb01776.x However, one study by

Guillermo Rougier Guillermo () is the Spanish form of the male given name William. The name is also commonly shortened to 'Guille' or, in Latin America, to nickname 'Memo'. People *Guillermo Amor (born 1967), Spanish football manager and former player *Guillermo A ...

has found it to lack the group's synapomorphies and instead resemble the American

stagodontids Stagodontidae is an extinct family of carnivorous metatherian mammals that inhabited North America and Europe during the late Cretaceous, and possibly to the Eocene in South America. Description Currently, the family includes four genera, ''E ...

more closely. Posterior phylogenetic studies have indeed recovered this specimen as being closer to the Marsupialiformes line than to Deltatheroida. However, instead of being close to stagodontids, the Gurlin Tsav skull usually groups outside of a clade leading to

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the souther ...

n metatherians (and, consequently, to

marsupial Marsupials are any members of the mammalian infraclass Marsupialia. All extant marsupials are endemic to Australasia, Wallacea and the Americas. A distinctive characteristic common to most of these species is that the young are carried in a ...

s). It is nearly always an immediate outgroup to

sparassodont Sparassodonta (from Greek to tear, rend; and , gen. , ' tooth) is an extinct order of carnivorous metatherian mammals native to South America, related to modern marsupials. They were once considered to be true marsupials, but are now tho ...

s. Most recently, it has been found to group with sparassodonts and other

Paleocene The Paleocene, ( ) or Palaeocene, is a geological epoch that lasted from about 66 to 56 million years ago (mya). It is the first epoch of the Paleogene Period in the modern Cenozoic Era. The name is a combination of the Ancient Greek ''pal ...

non-marsupial metatherians from South America. It and these taxa from a group independent from not only Deltatheroida, but also a North American clade where true marsupials are nested as well as stagodontids.

References

{{Metatheria, M. Prehistoric metatherians Maastrichtian life Cretaceous mammals of Asia Cretaceous Mongolia Fossils of Mongolia Nemegt Formation Undescribed vertebrate species