The genus Nemegtbaatar (Kielan-Jaworowska Z., 1974) is known by the species Nemegtbaatar gobiensis found in the Campanian (Upper Cretaceous) Barun Goyot Formation of Mongolia. "Compared to all extant mammals, the braincase in Nemegtbaatar and Chulsanbaatar is primitive." (Hurum, 1998). "All extant mammals" includes monotremes, 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, (ZPAL MgM-1/76).