陕西渭南西安犀的新材料

记述了产自陕西渭南县高湾沟牛寺庙白鹿原组中一新的两栖犀类———高湾沟西安犀(新种 ) (Sianodongaowangouensissp.nov.)。与已知的西安犀类头骨对比表明 ,新种与灞河西安犀 (S .bahoensis)最为接近。通过对已知两栖犀的前臼齿和臼齿列长度比较 ,认为两栖犀前臼齿和臼齿的变化趋势是较复杂的 ,非单一方向。根据白鹿原组中产出的几种哺乳动物与其他相关地层中的动物的对比 ,认为白鹿原组的时代可能为中始新世

NEW MATERIALS OF SIANODON FROM SHAANXI, CHINA

The specimen described in this paper was foundin Bailuyuan Formation in Weinan ,Shaanxi in 1 965.The left I2 ,allcanine ,premolars and molars were preserved ,but the frontal,parietal and occipital of the specimen were broken .The new material is referred to Sianodonaccording to the following characters:the diastema bet ween the canine and P2 relatively short,the external wall of the molar sflat,and the postglenoid and post tympanic processesin the ventral side of the skull farapart from each other.Thelength P2 P4/M1 M3ratiois larger than those of othe rspecies of the genus.There fore,anewspecies Siano dongaowang ouensissp .nov.is proposed .The diagnosis of the new species is:skull moderately large,three pair of incisors.the length of the upper premolars relatively large and near 1 / 2 of that of the uppermolars,the metaloph of M3 relatively short,the ectoloph extending for a short distance behind the metaloph ,the inner cingulum not well developed , and the inclination between paralop hand ectoloph of M2 and M3 70°and 60° ,respectively .