During pattern formation, morphogenetic events provide a response of the naïve tissue to chemical and mechanical positional cues. To what extent these processes shape pattern establishment and contribute to natural variation remains unclear. Marie and colleagues studied cell dynamics occurring during the emergence of feather array geometries in birds, which involves a gradual regionalisation of the skin through self-organisation. They identified highly dynamic modifications of local cell density, movement, and shape occurring during primordia emergence in the Japanese quail. Using inter-species comparison in poultry, finch, emu, ostrich and penguin embryos, followed by perturbation of skin architecture ex vivo, they showed that oriented anisotropy of dermal cells prior to primordia formation is necessary for the regularity of the final array. The results provide key insights into the cellular basis of self-organisation and demonstrate that initial tissue morphology constrains pattern attributes, uncovering a morphogenetic mechanism contributing to pattern evolution.