Abstract: The present paper discusses the age of the hominoid localities of Yuanmou based on the micromammals from these sites.
There is only a left upper premolar of Anourosores sp. from Loc. 8801.It is larger than the corresponding tooth of A. oblonnkus Storch&Qiu, 1990 from Lufeng, Yunnan.
An indeterminate Leporidae, represent by a fragment of upper cheek tooth from Loc. 8704 is the unique remain of Lagomorpha in the collections.
A right M1 or M2 of Sciurotamias sp. is obtained from Loc. 8801 and its morphology can be comparable to that of the same species from Lufeng.
Monosaulax sp. (Fig. 1) is quite common in this collection, represented by a right fragment of lower jaw with P4-M1, a left lower jaw with P4 and 16 isolated teeth from Loc. 8603, 8701, 8704, 8801 and 9001.The beaver is characterized by its subhyposodont cheek teeth and smooth surface of incisor in buccal side. Morphologically, it is close to Monosaulax sp. from Lufeng and easy to be distinguished from M.changpeiensis and M. tunguensis of North China by its larger size and higher crown.
Six isolated teeth from Loc. 8801 and 9001 are assigned to Brachyrhizomys blacki (Fig. 2, a-f, based on their dimension and height of crown, absent posterolingual enamel lake on M3, present distinct buccal curved upper molars and anterior slant lower molars. The Yuanmou Brachyrhizomys is distinguishable from B. cf. pilgrimi of Lufeng and Siwalik, and from B. choristos of Siwalik in smaller size, and from B. punjabiensis of Indian subcontinent in much larger size. Compared with B. shansius, the Yuanmou taxon is smaller and lower crowned. It differs from the Lufeng B. nagrii in mesolophid being weaker on M2, in having a developed mesolophid and not a combination of protoconid-hypolophid on M3 and from B.tetracharax in smaller size, much weaker mesolophid on M2 and a developed mesolophid on M3.
Size is slightly smaller and check teeth are somewhat narrower with much shorter mesolophid on M2 and poorer mure on M3 in B.micrus than in the Yuanmou form. In occlusal pattern of M2 and M3 the Yuanmou Brachyrhizomys resembles B. blacki except for its a bit larger size and more elongated M3 in the latter.
A right M2 collected from Loc. 8701 (Fig. 2, g), differs from Brachyrhizomys blacki of Yuanmou and B. tetracharax of Lufeng in larger dimension, higher crown and in having an isolatd mesolophid, which are here interpreted as being more progressive characters than those in B.tetracharax of Lufeng. It is impossible at the moment to place this specimen into any taxon of rhizomyids for the isolated mesolophid.
Additionally, the paper describes two fossil small mammals (Brachyrhizomys sp. and Muridae indet.) from Laoyatang southern Yuanmou basin.
The fossil small mammals collected from the northwest part of the Yuanmou basin seem to furnish no warrant of different age for the hominoid sites. An late Miocene age (later than that of Lufeng or equivalent to late Turolian of European Mammalian Age) is assumed for hominoid localities.

Key words: Yuanmou; Late Miocene; Micromammals