Plesiaceratherium

Abstract: In this paper a new species of Miocene rhinoceros is described.The specimens are collected from the Miocene of Shanwang in Lin Chu District,Shantung Province Plesiaceratherium shanwangensis sp.nov. Hypodigm:A left upper jaw with P~2-M~3,isolated p~1,p~3,M~3(dex.) and a frag- mental astragalus. Locality and Horizon:About 1 km to the east of Shanwang,Lin Chu District, Shantung;Shanwang Series (the left jaw and P~1 from coarse,dark yellow sandstone;P~3 M~3 and the fragmental astragalus from diatomaceous earth);M.Miocene. Diagnosis:Cheek teeth subhypsodont.Premolar comparatively short and wide, with antecrochet freguently joining with metaloph to form a mesofossette,exterior walls of premolar slightly convex and with two fibs;parastyle-fold undistinct and parastyle extends outwards;cingulum developed on the inner side,but absent on the exterior;p~3 and p~4 with a feeble,forked crochet.Molar protocones strongly constricted;ante- crochets developed,but not joined with metaloph;crochets also developed;interior cin- gulum represented merely by a tubercle at the entrance of mid-valley. Remarks:This new Shanwang species differs from Plesiaceratherium gracile from the same locality and horizon in having subhypsodont,larger cheek teeth, more developed interior cingulum,more molafized premolars,forked crochet of P~3 and P~4,etc. Furthermore the genus Plesiaceratherium (Young,1937) differs markedly from Brackypotaerium,a common Palarctic genus,in the structure of the cheek teeth and es- pecially in the limb bones.The occurrence of the latter genus in eastern Asia was first reported from the Hiramakian Miocene of Japan,represented by the species B.pugna- tot,which was later considered by Takai as a form of Chilotherium (1939).Recently Chow and Wang (1964) recorded the occurrence of B.cf.aureliense at Puchen near Nanking and another species from Hsiachaowan in northern Kiangsu,referring tentatively to B.pugnator.At the same time the authors pointed out that both the Japan and Hsia- chaowan forms are closer to Plesiaceratherium than Brachypotherium in the structure of the cheek teeth and might belong to the former genus.This inference is supported by a study of the new material described in the present paper.Therefore,the author suggests that the Hiramakian species should be named as Plesiaceratherium pugnator (new con- bination) and the Hsiachaowan form,which shows closer resemblance to the Shanwang form than to the Hiramakian form,should be referred likewise to this genus and species, i.e.Plesiaceratherium shanwangensis,sp.nov. The geological age of fossil-bearing Shanwang Series has been determined formerly as Late Miocene by Young (1937).Recently Young (1964) has suggested that it may be the earlier part of Late Miocene.In consideration of the new fact that Plesiacerathe- rium of Shanwang is comparable to or even more primitive than P.pugnator of Hira- makian of Japan,therefore,it might be Middle Miocene.