Abstract: The fossils of hominoids bearing locality at Shihuiba, Lufeng County, Yunnan province had been digged for eight seasons during 1975—1981. Mandibles of Ramapithecus and Sivapithecus of the following were unearthed. The three comparatively complete specimens of mandibles of Ramapithecus and four of Sivapithecus and more than 20 pieces of their fragments were studied and compared with those of extant large apes and those of related fossil specimens.
The main characters of mandibles of Ramapithecus and Sivapithecus from Lufeng are as follows:
1. The frontal part of the symphyseal region and the frontal teeth are almost vertically oriented.
2. The depths of the symphyseal region are large compared with those of the posterior of corpora.
3. The alveolar planes are moderately oblique.
4. The superior transverse tori are not pronounced.
5. The genioglossal fossae are of medium breadth.
6. The inferior transverse tori are strongly developed and the bottom of them slants postero-superiorly.
7. The depths of corpora at P4 and M3 are comparatively great.
8. The ascending rami are deep and broad and perpendicular to the corpora with their frontal margin relatively more in front.
Comparison of mandibles from Lufeng with those of the extant great apes suggests that they differ greatly from those of gorilla and chimpanzee, but close to that of orang-utan in five points as follows:
1. The frontal part of the symphyseal region and the frontal teeth are almost vertically oriented.
2. The alveolar planes are moderately oblique.
3. The superior transverse tori are not pronounced and the breadths of genioglossal fossae are medium.
4. They are well-matched in the depth and broadness of posterior parts of corpora and the relation of proportion in depth at the symphyseal region and the lateral part of corpora are comparatively similar between the Sivapithecus from Lufeng (PA 820) and the male orang-utan (No. 925).
5. The depth of ascending ramus of Sivapithecus from Lufeng corresponds to that of male orang-utan and the relation of proportion is comparatively similar between the depth of ascending ramus and that of corpora.
These resemblance between both further indicates that the two types of hominoids from Lufeng are most similar to orang-utan among the living great apes.
The mandibles of hominoids from Lufeng especially Ramapithecus when compared with those of Australo pith ecus present the following main similar characterisitics.
1. The frontal part of corpora and the frontal teeth are almost vertically oriented.
2. The sizes of frontal teeth particularly canines, are small and vertically oriented.
3. The cheek teeth are megadontic (relative to body size) with very thick enamel.
4. The bottoms of inferior transverse tori are oblique postero-superiorly and strongly projected backward.
5. The ascending rami are deep and broad.
In short, their common features are: their dentition possesses strong function of cutting and grinding; there are massive mandibular buttresses—the inferior transverse tori in inner side of the symphysis, and the ascending rami are deep and broad. These features may be the result of eating rough diet.
As many characteristics of two kinds of hominoids from Lufeng are similar to those of orang-utan, it seems to indicate that they have close relationships. These two kinds probably belong the same species with great sexual dimorphism. On the other hand, Ramapi- thecus from Lufeng also shows some features similar to Australopithecus. Thus, there is also possibility that Ramapithecus is a different taxon from Sivapithecus, and it is nearer to the common stock of man and African large apes.

Key words: Ramapithecus; Sivapithecus； Hominoid; Ancestor of orang-utan; Late Miocene; Lufeng