title: A short-armed troodontid dinosaur from the Upper Cretaceous of Inner Mongolia and its implications for troodontid evolution.
abstract: BACKGROUND
  The Troodontidae represents one of the most bird-like theropod groups and plays an important role in our understanding of avian origins. Although troodontids have been known for over 150 years, few known derived troodontid specimens preserve significant portions of both the forelimb and the hindlimb.
  
  
  RESULTS
  Here, we report a new troodontid taxon, Linhevenator tani gen. et sp. nov., based on a partial, semi-articulated skeleton recovered from the Upper Cretaceous Wulansuhai Formation of Wulatehouqi, Inner Mongolia, China. L. tani has an unusual combination of primitive and derived character states, though our phylogenetic analysis places it in a derived clade within the Troodontidae. As a derived taxon, L. tani has a dromaeosaurid-like pedal digit II, and this species also possesses a humerus that is proportionally much shorter and more robust than those of most other troodontids.
  
  
  CONCLUSIONS
  The combination of features present in Linhevenator indicates a complex pattern of character evolution within the Troodontidae. In particular, the discovery of Linhevenator suggests that derived troodontids have independently evolved a highly specialized pedal digit II and have significantly shortened the forelimb over the course of their evolution.
authors.affiliation: Key Laboratory of Evolutionary Systematics of Vertebrates, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing, China. xingxu@vip.sina.com
authors.forename: Xing
authors.initials: X
authors.lastname: Xu
authors.forename: Qingwei
authors.initials: Q
authors.lastname: Tan
authors.forename: Corwin
authors.initials: C
authors.lastname: Sullivan
authors.forename: Fenglu
authors.initials: F
authors.lastname: Han
authors.forename: Dong
authors.initials: D
authors.lastname: Xiao
mesh_terms: D000818:Animals; D005075:Biological Evolution; D002681:China; D025061:Dinosaurs / Q000145:classification*; D005552:Forelimb; D006614:Hindlimb; D010802:Phylogeny