Hackett et al.: A Phylogenomic Study of Birds Reveals Their Evolutionary History. Science 27-06-2008: Vol. 320. No. 5884, pp. 1763–1768 doi:10.1126/science.1157704
Erich D. Jarvis et al.: Whole-genome analyses resolve early branches in the tree of life of modern birds. 12-12-2014, Science, 346 (6215), doi:10.1126/science.1253451