Nature 496, 498–503 (2013); doi:10.1038/nature12111

In this Letter, five authors were inadvertently omitted: Sharmin Begum and Christine Lloyd from the Wellcome Trust Sanger Institute, and Christa Lanz, Günter Raddatz and Stephan C. Schuster from the Max Planck Institute for Developmental Biology. David Elliot was incorrectly listed as David Eliot, Beverley Mortimore was incorrectly listed as Beverly Mortimer, and James D. Cooper was incorrectly listed as James Cooper. In addition, the acknowledgements section should state that author S.C.S. was supported by the German Research Foundation (DFG Grant NU 22/5). These errors, along with corresponding minor changes to the Author Contributions section, have been corrected in the HTML and PDF versions of the original manuscript.