Tombaatar
Scientific classification
Kingdom: Animalia
Therapsida
Class: Mammalia
Order: Multituberculata
Family: Djadochtatheriidae
Genus: Tombaatar
Species
  T. sabuli

Ref.

Tombaatar is a mammal genus that during the Mongolian Upper Cretaceous. It coexisted with some of the late dinosaurs. This animal was a member of the extinct order of Multituberculata.
For those of a technical disposition, it's within the suborder of Cimolodonta, and a member of the family Djadochtatheriidae.

Genus: Tombaatar Rougier GW, Novacek M & Dashzeveg D, 1997

Species: Tombaatar sabuli Rougier GW, Novacek M & Dashzeveg D, 1997
Place: Djadokhta Formation, Ukhaa Tolgod
Country: Mongolia
Age: Upper Cretaceous
Remarks: Tombaatar was a relatively large multituberculate. The skull's perhaps 6cm in length.
Reference: Rougier, Novacek & Dashzeveg (1997), A new multituberculate from the late Cretaceous locality Ukhaa Tolgod, Mongolia: Considerations on multituberculate interrelationships. American Museum Novitates 3191, p.1-26.

Page reference: 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)