镰刀龙类 (又称“懒龙”)是一类奇特的植食性兽脚类恐龙 ,化石记录主要局限于亚洲白垩纪地层中。由于镰刀龙类极其特化的形态和化石材料的局限性 ,这类恐龙的系统位置存在较多的争议。最近的发现 (RussellandDong ,1 994;Xuetal.,1 999)表明这类恐龙属于虚骨龙类 ,但其更为具体的系统位置依然存在争议 (Sues ,1 997;MakovickyandSues,1 998;Xuetal.,1 999;Sereno,1 999)。新发现于内蒙古苏尼特左旗赛罕高毕上白垩统二连组的镰刀龙类化石材料代表这类恐龙的一个新属种。杨氏内蒙古龙 (Neimongosaurusyangigen .etsp .nov .)的正型标本为一较为完整的骨架 ,是已知镰刀龙类当中第一件在同一个体中保存了大多数脊椎和几乎所有肢骨的标本。依据以下特征将内蒙古龙归入镰刀龙超科 :U形的下颌联合部、齿骨前端向下弯曲、齿骨前部没有牙齿、牙齿有一个收缩的基部、近圆形的齿根和叶形的齿冠、前部颈椎的神经脊低矮而轴向较长、后部颈椎背视呈X形、肱骨近端角状、肱骨有后转子、肱骨的尺骨髁和挠骨髁位于前部并为一狭窄槽分开、肠骨的耻骨柄细长而坐骨柄短以及跖部短。内蒙古龙的以下特征区别于其他镰刀龙类 :前部尾椎的横突下部有一圆形的窝 ,桡骨二头肌结节非常发育 ,后足趾节近端跟部非常发育 ,胫骨的腓骨嵴长 The sickle dragon (also known as “lazy dragon”) is a peculiar herbivorous plant-eating dinosaur that is confined mainly to the Cretaceous in Asia. Because of the extremely specialized morphology of fusidosaurian species and the limitations of fossil materials, there is much controversy about the systematic location of such dinosaurs. Recent discoveries (Russelland Dong, 1994; Xu et al., 1999) suggest that these dinosaurs are copepodids, but their more specific system positions remain controversial (Sues, 1997; Makovicky and Sues, 1998; Xu et al, 1 999; Sereno, 1 999). The newly discovered fossil dinosaur from the Cretaceous Erlian Formation in the Upper Saihangao of Sunit Left Banner in Inner Mongolia represents a new species of this kind of dinosaur. The positive specimen of Neimongosaurus yangyanggen s. P. Nov. Is a relatively complete skeleton. It is the first specimen known to retain most spines and almost all limb bones in the same individual. According to the following characteristics, the Inner Mongolian dragon was classified as a sickle superfamily: the U-shaped mandibular joint, the anterior front of the bone was bent downward, the anterior teeth had no teeth, the teeth had a constricted base, nearly rounded roots and leaves Of the cusp, the anterior cervical spine low and axial long spinal cord, posterior cervical spine was X-shaped, proximal humeral angle, the posterior humerus rotor, ulnar and humeral condyles in the front and Separated by a narrow slot, the pubic bone is long and the stem is short and the plantar part short. The following characteristics of the Inner Mongolia dragon are distinguished from other sickle dragons: the anterior coccyx has a circular socket in the lower part of the transverse process, the radial biceps nodules are well developed, the proximal heel toe section is well developed, the tibia fibular crista long