Dinosaur skull geometry does not follow functional optimization trends but facilitates adaptability.

Dinosaurs exhibited a remarkable array of skull shapes and sizes. However, the geometry of the cranial skeleton and its different functional units (rostrum, orbital region, and braincase) has not been quantified biomechanically. Furthermore, it is unclear if skull evolution followed a trend toward optimization of feeding performance and structural integrity. Here, we used morphometric analyses, theoretical morphospaces, and biomechanical modeling to quantify skull geometry and investigate how skull proportions shaped dinosaur evolution. Our results demonstrate that skull proportions followed a narrowly constrained pattern, with the rostrum showing the largest variability and plasticity. Dinosaur skulls did not evolve toward functional optimality but evolved within a "Goldilocks" zone that represented a compromise of different functions. Broad adaptability of the rostrum may have been beneficial during the transition from non-avian dinosaurs to birds, with the rostrum serving as a focal point for environmental manipulation due to the loss of forelimb function for flight.