Gastrulation involves the conversion of pluripotent epiblast cells through transcriptional, epigenetic, and functional diversification. As individual embryos can be considered unique time points along a shared time axis, sampling single cells from single embryos has recently enabled us to construct time-resolved flow models of mouse and rabbit gastrulation that consider continuous, parallel, and converged differentiation towards multiple lineages. In the coming years, by comparing and manipulating differentiation flows between species, we wish to dissect the interface between structure and function at an evolutionary and molecular level.