The sequencing of platypus was funded by the National Human Genome Research Institute (NHGRI). This research was supported by grant HG002238 from the NHGRI (W.M.), NGFN (0313358A; to J.S. and J.B.), the DFG (SCHM 1469; to J.S. and J.B.), National Science Foundation BCS-0218338 (M.A.B.) and EPS-0346411 (M.A.B.), National Institutes of Health RO1 GM59290 (M.A.B.), National Institutes of Health RO1HG02385 (E.E.E), Australian Research Council (F.G.), UK Medical Research Council (C.P.P. and A.H.), Ministry of Science-Spain (X.S.P. and C.L.-O.) and the State of Louisiana Board of Regents Support Fund (M.A.B.). We thank T. Grant, S. Akiyama, P. Temple-Smith, R. Whittington and the Queensland Museum for platypus sample collection and DNA, and Macquarie Generation and Glenrock station for providing access and facilities during sampling. Approval to collect animals was granted by the New South Wales National Parks and Wildlife Services, New South Wales. Funding support for some platypus samples was provided by Australian Research Council and W.V. Scott Foundation. We thank M. Shelton, I. Elton and the Healesville Sanctuary for platypus pictures. We thank L. Duret for assistance on genome landscape analysis; G. Shaw for use of the silhouettes on Fig. 1; and Z.-X. Luo, M. Archer and R. Beck for advice on the Fig. 1 phylogeny. We acknowledge the approved use of the green anole lizard sequence data provided by the Broad Institute. Resources for exploring the sequence and annotation data are available on browser displays available at UCSC (http://genome.ucsc.edu), Ensembl (http://www.ensembl.org) and the NCBI (http://www.ncbi.nlm.nih.gov).