Nemegtbaatar is a genus of mammal

Mammal

Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...

 from the Upper 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...

 Period of what is now Mongolia

Mongolia

Mongolia is a landlocked country in East and Central Asia. It is bordered by Russia to the north and China to the south, east and west. Although Mongolia does not share a border with Kazakhstan, its western-most point is only from Kazakhstan's eastern tip. Ulan Bator, the capital and largest...

. It existed in the company of much larger dinosaur

Dinosaur

Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...

s, found together in the Nemegt Basin

Nemegt Basin

The Nemegt Basin is situated in the northwestern part of the Gobi Desert, in the Ömnögovi Province in the southern part of Mongolia. It is known locally as the valley of the dragons, since it is a source of many fossil finds, including dinosaurs, dinosaur eggs and trace fossils.The main geological...

. This creature was a member of the extinct order Multituberculata

Multituberculata

The Multituberculata were a group of rodent-like mammals that existed for approximately one hundred and twenty million years—the longest fossil history of any mammal lineage—but were eventually outcompeted by rodents, becoming extinct during the early Oligocene. At least 200 species are...

. It's within the suborder Cimolodonta

Cimolodonta

The Cimolodonta are a taxon of extinct mammals that lived from the Cretaceous to the Eocene. They were some of the more derived members of the extinct order Multituberculata. They probably lived something of a rodent-like existence until their ecological niche was assumed by true rodents...

 and is a member of the superfamily Djadochtatherioidea

Djadochtatherioidea

Djadochtatherioidea is a group of extinct mammals known from the upper Cretaceous of Central Asia. They were members of an also extinct order called Multituberculata. These were generally small, somewhat rodent-like creatures, who scurried around during the "age of the dinosaurs". Unusually for...

.

The genus Nemegtbaatar (Kielan-Jaworowska Z., 1974) is known by the species Nemegtbaatar gobiensis found in the Campanian (Upper Cretaceous) Barun Goyot Formation

Barun Goyot Formation

The Barun Goyot Formation , dating from the Late Cretaceous Period, is located within and is widely represented in the Gobi Desert basin, in the Ömnögovi Province of Mongolia....

 of Mongolia. "Compared to all extant mammals, the braincase in Nemegtbaatar and Chulsanbaatar

Chulsanbaatar

Chulsanbaatar is a genus of mammal from the Cretaceous of Mongolia. It lived during the Mesozoic, also known as the "age of the dinosaurs." This small creature was a member of the extinct order of Multituberculata and is within the suborder Cimolodonta. The genus Chulsanbaatar was named by...

is primitive." (Hurum, 1998). "All extant mammals" includes monotreme

Monotreme

Monotremes are mammals that lay eggs instead of giving birth to live young like marsupials and placental mammals...

s, such as the duck-billed platypus, despite its residual egg-laying habit.

Nemegtbaatar was a relatively large member of Djadochtatherioidea, with a skull length of up to 4.5 cm. At least one specimen is in the Institute of Paleobiology collection of the Polish Academy of Science at Warsaw

Warsaw

Warsaw is the capital and largest city of Poland. It is located on the Vistula River, roughly from the Baltic Sea and from the Carpathian Mountains. Its population in 2010 was estimated at 1,716,855 residents with a greater metropolitan area of 2,631,902 residents, making Warsaw the 10th most...

, (ZPAL MgM-1/76).