Owing to their distinct ecological, anatomical and physiological features, monotremes are interesting mammals well-suited for the study of the evolution of ecological adaptation. Platypuses and echidnas feature radical differences in diet (carnivorous compared with insectivorous), neurophysiology (electroreception-oriented compared with olfaction-oriented), as well as specific intraspecific conflict and defence adaptations 1. aculeatus and three Zaglossus spp.) are present in Australia and New Guinea ( Supplementary Information). At present, the single species of platypus has a restricted distribution in Eastern Australia, whereas four echidna species ( T. The monotreme lineage comprises two extant families, the semi-aquatic Ornithorhynchidae (platypus) and the terrestrial Tachyglossidae (echidna). The iconic egg-laying monotremes of Australasia represent one of the three major mammalian lineages. Further comparative genomic analyses unravel marked differences between monotremes and therians in haptoglobin genes, lactation genes and chemosensory receptor genes for smell and taste that underlie the ecological adaptation of monotremes. The formation of such a unique chromosome complex may have been facilitated by the unusually extensive interactions between the multi-X and multi-Y chromosomes that are shared by the autosomal homologues in humans. We provide evidence that the monotreme sex chromosome complex originated from an ancestral chromosome ring configuration. Together with our echidna sequence, the genomes of the two species allow us to detect the ancestral and lineage-specific genomic changes that shape both monotreme and mammalian evolution. The nearly complete platypus genome assembly has anchored almost the entire genome onto chromosomes, markedly improving the genome continuity and gene annotation. Here we generate and analyse reference genomes of the platypus ( Ornithorhynchus anatinus) and echidna ( Tachyglossus aculeatus), which represent the only two extant monotreme lineages. Nature volumeВ 592, pages 756вЂ“762 ( 2021) Cite this articleД®gg-laying mammals (monotremes) are the only extant mammalian outgroup to therians (marsupial and eutherian animals) and provide key insights into mammalian evolution 1, 2. Platypus and echidna genomes reveal mammalian biology and evolution

Platypus evolution ornithorax