Chulsanbaatar
Scientific classification
Kingdom: Animalia
Therapsida
Class: Mammalia
Order: Multituberculata
Superfamily: Djadochtatherioidea
Genus:Chulsanbaatar
Species
  C. vulgaris

Ref.

Chulsanbaatar is a genus of mammal from the Upper Cretaceous of Mongolia. It lived in the company of dinosaurs. This small creature was a member of the extinct order of Multituberculata.
For those of a technical inclination, it's within the Suborder of Cimolodonta, and a member of the superfamily Djadochtatherioidea.

Genus: Chulsanbaatar Kielan-Jaworowska Z, 1974

Species: Chulsanbaatar vulgaris Kielan-Jaworowska Z, 1974
Place: Red Beds, Hermiin Tsav (aka Khermeen Tsav)
Country: Mongolia
Age: Campanian (late?), Upper Cretaceous
Remarks: A multi midget with a 2cm skull. The jaw would fit on your fingertip. Remarkably, it’s been possible to study the ear bones, which shows how well some of the fossils are preserved. Chulsanbaatar is now a resident of the Polish Academy of Science at Warsaw, (eg. ZPAL MgM-1/84). There are a fair number of specimens in the collection, which doubtless accounts for the species name. Vulgaris = common.
Reference: Kielan-Jaworowska (1974), Multituberculate succession in the Late Cretaceous of the Gobi Desert (Mongolia). Palaeontologica Polonica, 30, p.23-44.

Page references: Kielan-Jaworowska Z & Hurum JH (2001), Phylogeny and Systematics of multituberculate mammals. Paleontology 44, p.389-429.

(This information has been derived from [1] MESOZOIC MAMMALS; Djadochtatherioidea, an internet directory. As that's my webpage, there are no issues of copyright. Trevor Dykes)