Abstract

One of the central questions in evolutionary biology is how new morphological innovations arise. Despite major advances integrating paleontology, genomics, and developmental biology, we still lack a mechanistic understanding of how novel traits emerge and diversify from highly constrained genomic and developmental programs. To address this question, we use bats as a model system, leveraging their exceptional ecological and morphological diversity. Combining morphological, genomic, developmental, and modeling approaches across multiple species, we investigate the origin and diversification of mammalian tooth classes, a key evolutionary innovation underlying dietary diversification. I will first present new results on molar diversification, showing that molar morphology evolves along distinct developmental trajectories that both follow and break conserved developmental constraints. I will then introduce our work on the developmental cascades that pattern tooth classes, and present a predictive model explaining the diversification of premolar and molar proportions through interacting developmental rules. Finally, I will also briefly explore the evolution of deciduous (milk) teeth in bats, highlighting how their highly specialized morphology, shaped by functional constraints related to early life history, provides a complementary perspective on how developmental programs can be repurposed across life stages. Together, our results show that developmental constraints do not simply limit evolution, but actively structure the space of possible phenotypes by channeling variation along specific trajectories, while allowing occasional shifts that generate novel morphologies. These dynamics emerge from the interplay between conserved developmental modules and more labile components of gene regulatory networks. Altogether, this framework highlights how morphological innovation arises not from the release of constraints, but from their modulation across developmental time, providing a general mechanism for the evolution of serial organs.