Abstract: Yixianosaurus longimanus is a small theropod from the Lower Cretaceous of western Liaoning Province, China. It was originally suggested to be a derived maniraptoran, but this interpretation was challenged by a recent study that proposed instead that Y. longimanus was a basal maniraptoran. Given that the systematic position of this taxon will affect our understanding of such broad issues as the evolution of the theropod forelimb and plumage, it is important to carefully evaluate both systematic hypotheses and determine which is better supported. Here we review all available morphological features in Y. longimanus that appear informative with regard to its systematic position. We demonstrate that this small theropod is a basal paravian and most likely a basal deinonychosaurian, a result that conforms to the original interpretation of this specimen. The hypothesis that Y. longimanus is a basal paravian is consistent with the probable presence of pennaceous feathers in this taxon, and avoids implying a complicated evolutionary history for the maniraptoran forelimb.

摘要： 长掌义县龙(Yixianosaurus longimanus)是发现于中国辽西下白垩统的一种小型兽脚类恐龙。最初的研究认为它代表一种进步的手盗龙类，但最近的一项研究工作质疑了这一系统发育假说，新的系统发育研究认为长掌义县龙代表一种原始的手盗龙类。鉴于长掌义县龙的系统位置会影响我们对兽脚类前肢和羽毛演化等关键问题的理解，因此需要评估哪一个系统发育假说更为可靠。本文评述了长掌义县龙所有可被用于系统发育研究的形态学特征，证明了这一小型兽脚类恐龙属于基干副鸟类，并很可能属于基干恐爪龙类。这一结论与最初的研究结果相吻合。这一系统位置也与长掌义县龙可能具片状羽毛相吻合，并且否定了手盗龙类前肢演化历史复杂的假说。