1. Institute of Vertebrate Paleontology and Paleoanthropology, Academia Sinica, PO Box 643, Beijing 100044, People's Republic of China
2. Natural History Museum, Changchun University of Science and Technology, No. 6 Ximingzhu Street, Changchun, 130026, People's Republic of China

Correspondence to: Correspondence and requests for materials should be addressed to X.X. (e-mail: Email: xxu@sun.midwest.com.cn).

Abstract

Therizinosauroidea ('segnosaurs') are little-known group of Asian dinosaurs with an unusual combination of features that, until recently, obscured their evolutionary relationships. Suggested affinities include Ornithischia¹, Sauropodomorpha²,³, Theropoda^{4, 5, 6, 7, 8, 9, 10, 11} and Saurischia sedis mutabilis ¹². Here we describe a new therizinosauroid from the Yixian Formation (Early Cretaceous, Liaoning, China)¹³. This new taxon provides fresh evidence that therizinosauroids are nested within the coelurosaurian theropods^{8, 9, 10, 11}. Our analysis suggests that several specialized therizinosauroid characters, such as the Sauropodomorpha-like tetradactyl pes¹,², evolved independently within this group. Most interestingly, this new dinosaur has integumentary filaments as in Sinosauropteryx ¹⁴,¹⁵. This indicates that such feather-like structures may have a broad distribution among non-avian theropods, and supports the hypothesis that the filamentous integumentary structures may be homologous to the feathers of birds¹⁴,¹⁵.