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Duckbill Platypus, painted by San Francisco Bay artist, Pat Sherwood. As the most ancestral mammalian relatives of humans, the egg-laying monotremes, the platypus and echidna, offer insight into events that occurred at the dawn of mammalian evolution. Killian et al. demonstrate in this issue that IGF2 is not imprinted in monotremes, providing the first compelling evidence that the phylogenetic breadth of this epigenetic gene regulatory phenomenon is restricted to marsupials and placental mammals.