Abstract: 聽We re-examine the partial skeleton of the enigmatic small feathered theropodYixianosaurus聽longimanus聽from the Lower Yixian Formation, China. A phylogenetic analysis recovers聽Yixianosaurus聽as a basal maniraptoran, in a polytomy withAlvarezsaurus, Therizinosauria, Alvarezsauroidea excluding聽Alvarezsaurus, and a well-resolved clade of derived maniraptorans including Oviraptorosauria and Paraves. The blend in聽Yixianosaurus聽of primitive traits, such as a low brachial index and robust digit III, and derived traits such as a subrectangular coracoid,聽suggests a more complicated mosaic of forelimb evolution within Maniraptora than previously proposed. The robust forelimb bones and massive, recurved, and pointed manual unguals suggest聽Yixianosauruswas predatory, although this assessment remains tentative until more complete fossils of this taxon are found. The basal maniraptoran phylogenetic position implies a larger range of forelimb morphologies at this point in coelurosaurian evolution. In many ways, the robust forelimb and hypertrophied recurved unguals are similar to those of聽Tanycolagreusand聽Coelurus,聽and may be morphologically transitional between these taxa and basal therizinosaurs and oviraptorosaurs. The presence of large, veined, pennaceous contour feathers on聽Yixianosaurus聽indicates the origin of these integumentary structures may be deeper in coelurosaur phylogeny than previously reported. Finally, the robust, elongate forelimbs suggest a different ecological role than inferred for other sympatric small theropods, and lend support to the idea of niche partitioning among the small non-avian theropods of the Jehol聽fauna.聽

摘要： 重新研究了产于辽西义县组下部的带羽毛小型兽脚类恐龙长掌义县龙(Yixianosaurus longimanus)的不完整骨架。系统发育分析得出义县龙属于手盗龙类基干类群，与阿尔瓦雷斯龙(Alvarezsaurus)、镰刀龙类、除阿尔瓦雷斯龙之外的其他阿尔瓦雷斯龙类以及由窃蛋龙类和副鸟龙类等进步手盗龙类组成的一个类群形成多分支状态。义县龙既有原始特征，如臂指数低，第三指强壮；也有进步特征，如乌喙骨近长方形，表明在手盗龙类当中，前肢演化呈现出比以前认为的更加复杂的镶嵌现象。强壮的前肢骨骼以及厚重、弯曲而尖利的手爪表明义县龙是捕食者，尽管这一认识尚待该属种更完整化石的发现来证实。义县龙在手盗龙类系统发育中的基部位置暗示，在虚骨龙类演化的这一节点上，前肢形态的变异范围更大。在许多方面，义县龙强壮的前肢和过度增大的弯曲爪子与长臂猎龙(Tanycolagreus)和虚骨龙(Coelurus)的相似，可能代表了这些属种与基干镰刀龙类和窃蛋龙类之间的过渡形态。义县龙保存了大的片状体羽，表明这些皮肤衍生物在虚骨龙类中的起源可能比以前报道的要早。最后，强壮而伸长的前肢暗示了其生态功能与根据同一区域的其他小型兽脚类推测的不同，支持了热河生物群的小型非鸟兽脚类中存在小生境划分的观点。