Lateral inhibition governs ancestral cellular patterning in fossil and extant liverworts

The incompleteness of the fossil record and the absence of genetic information limit our ability to understand ancient developmental processes and reconstruct their evolution. Here, we use comparative and mathematical analyses to uncover an evolutionarily conserved patterning mechanism underlying liverwort oil body cell specification. We demonstrate that patterns of oil body cell homologs in fossils of the oldest known liverwort (Metzgeriothallus sharonae) exhibit the spatial organization characteristic of lateral inhibition. A mechanism with local activation and lateral inhibition not only reproduces the patterns observed in fossils, but also oil body cell patterns in the extant liverworts Treubia lacunosa, Apotreubia nana, and Marchantia polymorpha. Our results point to an ancestral patterning mechanism that has been modulated by lineage-specific selective pressures over evolutionary time.