New material of Rhinopithecus lantianensis from Yunxi, Hubei Province and its geochronological singificance
PAN Yue-rong
2001, 20(02):
92-101.
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New material of Rhinopithecus lantianens is including an almost complete mandible with complete dentition except for I1, I2, left M2 and M3, was found from the Yangweizhen locality of Yunxi county, Hubei province. The mandibular ramus and corpus are broken at the level of left M2 and right M3. The specimen is somewhat distorted at P3.
The lower canine is high-crowned and robust. A mesial ridge passes from the base of the crown to the apex of the crown. Distally there is awear facet, produced by the honing action of the upper canine. On the basis of size and morphological characteristics it is assumed this mandible belonged to a male individual.
The lower premolars are large. The P3 is not so sectorial in shape as cercopithecines. A relatively wide P3 is characteristic of colobines that shows tiny protoconid and metaconid,with extension of enamel on to the cervical border of the mesial root. The P4 is relatively short and wide. The protoconid and metaconid are relatively large and the metaconid is higher than the protoconid with wear as in the lower molars. The talonid fovea is relatively low and narrow.
The lower molars with relatively short trigonids are large both in length and width.The lingual aspects of the lower molars present highly relief and deeply incised lingual notches, highly characterister of heavily worn colobine molars, that larger areas of dentine are exposed on the buccal cusps and only small dentine point exposed on the lingual cusps. The M1 is smaller than M2 and M3 and the anterior part of the crown is smaller than posterior one in M1 and almost the same size in M2. In addition, there are accessory cuspletes on the hypoconulid of the M3.
The mandibular body is high and thick. In the buccal view there is a thick inflation from the lower part of canine extending to the lower margin of mandibular body so that the lower margin of mandibular body increases in thickness exhibiting torus-shaped.Both the thickness and the height are greatest at the level of mandibular symphysis, that is 20mm thick and 52.0mm high. There is awell-developed fossa genioglossi in the lingual surface of the symphyseal region.
Measurements of the dentition and mandibular body indicated that Rhinopithecus lantianensis from three localities, Gongwangling, Yunxian and Yunxi, are larger than Rhinopithecus roxellanae tingianus from Yanjinggou.The height of Rhinopithecus lantianensis from Yunxi at M1 is 47.7mm, much larger than that of R.roxellanae tingianus ( 30.5mm). As mentioned above, Rhinopitheus lantianensis differs from Rhinopithecus roxellanae tingianus from middle-late Pleistocene in the following respects:larger- sized teeth, sub-sectorial P3, a relatively short and wide P4.The lower canine is high-crowned and robust.The lower teeth are small relatively to the size of mandiblar body.It seems to suggest a evolutionary trend for Rhinopithecus i.e.the robust degree of the canine is getting decrease, the P3 become sectorial-shaped, the two main cusps of the P4 are higher.Also the lower molars shown highly characteristic of heavily worn colobine molars.The mandibular body decrease both in height and thickness.
Geographically,Gongwangling and Yunxian localities are located respectively at the northern and southern slope of the Qinling area which is the boundary of North and South China even East Asia or temperate and subtropic-tropic zones at present. Mammalian fossils of both Gongwangling and Yunxian both come from the deposit of river terrace and associated with Homo erectus. Biostratigraphically, they can be attributed to the lower Pleistocene. Otherwise, Gongwangling locality can be back to 1.15 Ma based on the research of paleomagnetic and lithostratigraphic position of the fossils in the loess-paleosol sequence, the Yunxian locality may be older than 0.8 Ma based on the paleomagnetic study.Significantly, both Gongwangling and Yunxian faunas which associated with Rhinopithecus lantianensis both are mixtures of northern and southern elements.Therefore, Rhinopithecus lantienensis can be a good indicator for the climatic fluctuations during the Pleistocene.The distribution of Rhinopithecus lantianensis suggests that the Qingling Range is an important area for the evolution of Rhinopihecus.
