Abstract:  A completely preserved mandible of Leptobos from the Early Pleistocene mammalian fauna of Longdan, Gansu Province, China, is described here. The mandible has a long thin mandibular body, and a long mandibular diastema. The premolar row is short. The mandibular body forms an obtuse angle of about 120° with the mandibular ramus, while the angle of the mandible is nearly 90°. The paraconid and parastylid are well developed, and the metaconid extends posteriorly, not connecting with the paraconid in p3 or p4. The main cusps of the molars are rounded, and ectostylids (basal pillars) present in m1-m3. The metastylid of m2 is weak, and the preprotocristids of m2-m3 and posthypocristid of m3 are anteroposteriorly constricted. Skulls of Leptobos brevicornis were previously discovered in the same area, and the new specimen is also attributable to this species. Wounds preserved in the anterior part of the mandible are interpreted as resulted from attack by a feline predator, indicating the predatory behavior similar to that of living big cats, using muzzle clamps to suffocate preys, may have already occurred in the Early Pleistocene.  

摘要： 记述了甘肃龙担早更新世哺乳动物群中首次发现的一件丽牛(Leptobos)下颌骨，这是我国目前发现的保存最为完整的丽牛下颌材料。依据p3、p4的下前尖与下前附尖分离，下后尖向后延伸不与下前尖愈合，m1？m3的下后尖和下内尖冠面形状近于圆形，连续发育有下外附尖，m2的下后附尖弱，m2和m3的下原尖和下次尖有前后向收缩等特征，以及相同地点产出的短角丽牛头骨，将新材料归为Leptobos brevicornis。新材料补充了丽牛的下颌形态特征：下颌骨水平支窄长，齿槽间隙对颊齿齿列的比例大，前臼齿列短，水平支与垂直支之间的夹角约为120°，下颌角约呈90°。这件下颌骨的前端保留有食肉动物袭击的痕迹，该伤痕可以被解释为由大型虎亚科动物攻击丽牛时犬齿刺穿形成。这样的骨骼证据表明，攻击猎物口鼻部而使猎物窒息死亡，这种与现生大型猫科动物类似的捕食行为在早更新世的虎亚科动物中已经出现。