1. Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing 100044, China
2. American Museum of Natural History, Central Park West at 79th Street, New York, New York 10024, USA
3. The Field Museum, 1400 S Lake Shore Drive, Chicago, Illinois 60605, USA
4. Canadian Museum of Nature, Station D, Ottawa, Ontario K1P 6P4, Canada

Correspondence to: Xing Xu¹ Correspondence and requests for materials should be addressed to X.X. (e-mail: Email: xxu@midwest.com.cn) or M.A.N. (e-mail: Email: norell@amnh.org).

Abstract

Troodontid dinosaurs form one of the most avian-like dinosaur groups^{1, 2, 3, 4, 5}. Their phylogenetic position is hotly debated, and they have been allied with almost all principal coelurosaurian lineages^{6, 7, 8, 9, 10, 11, 12, 13}. Here we report a basal troodontid dinosaur, Sinovenator changii gen. et sp. nov., from the lower Yixian Formation of China. This taxon has several features that are not found in more derived troodontids, but that occur in dromaeosaurids and avialans. The discovery of Sinovenator and the examination of character distributions along the maniraptoran lineage indicate that principal structural modifications toward avians were acquired in the early stages of maniraptoran evolution.