The alvarezsauroid theropod Linhenykus monodactylus from the Upper Cretaceous of Inner Mongolia, China is the first knownmonodactyl non−avian dinosaur, providing important information on the complex patterns of manual evolution seen in alvarezsauroids. Herewe provide a detailed description of the osteology of this taxon. Linhenykus shows a number of features that are transitional between parvicursorine and non−parvicursorine alvarezsauroids, but detailed comparisons also reveal that some characters had a more complex distribution. We also use event−based tree−fitting to perform a quantitative analysis of alvarezsauroid biogeography incorporating several recently discovered taxa. The results suggest that there is no statistical support for previous biogeographic hypotheses that favour pure vicariance or pure dispersal scenarios as explanations for the distributions of alvarezsauroids across SouthAmerica, NorthAmerica andAsia. Instead, statistically significant biogeographic reconstructions suggest a dominant role for sympatric (or “within area”) events, combined with a mix of vicariance, dispersal and regional extinction. At present the alvarezsauroid data set is too small to completely resolve the biogeographic history of this group: future studies will need to create larger data sets that encompass additional clades.

Key words: Dinosauria, Theropoda, Parvicursorinae, alvarezsauroid biogeography, Treefitter, dispersal, vicariance, sympatry, Cretaceous, Wulansuhai Formation, Inner Mongolia, China.

Xing Xu [xingxu@vip.sina.com], Qingyu Ma [maqingyu.ivpp@gmail.com], Corwin Sullivan [csullivan@ivpp.ac.cn], David W.E.Hone [dwe_hone@yahoo.com], and Fenglu Han [hfl0501@gmail.com], Key Laboratory of Evolutionary Systematics of Vertebrates, Institute of Vertebrate Paleontology & Paleoanthropology, Chinese Academy of Sciences, 142 Xiwai Street, Beijing 100044, China; Paul Upchurch [p.upchurch@ucl.ac.uk] and Michael Pittman [mdpittman@hotmail.com], Department of Earth Sciences, University College London, Gower Street, London, WC1E 6BT, UK; Jonah Choiniere [jonah.choiniere@gmail.com], Department of Biological Sciences, George Washington University, 2023 G Street NW, Washington, DC 20052, USA; Qingwei Tan [firsttan@sina.com] and Lin Tan, Long Hao Institute of Geology and Paleontology, Hohhot, Nei Mongol 010010, China; Dong Xiao, Department of Land and Resources, Linhe, Nei Mongol 015000, China.