Fig. 1: Endocranial and landmark sampling for this study.

a Endocranial reconstructions of neonate, intermediate, and mature specimens of Gallus, Psittacosaurus, and Alligator in lateral view. The intermediate ontogenetic representatives illustrate morphological transitions, not equivalent growth stages across taxa. Scale bars equal 5 mm. b time-calibrated phylogeny showing the taxonomic sampling of this study, where branches are color coded by major groups. Asterisks indicate taxa represented by immature specimens. c landmark scheme projected on the endocranial reconstruction of Psittacosaurus hatchling (IVPP V15451), where red, yellow, and blue coordinate points denote fixed, curve, and surface semi-landmarks in oblique (top), lateral (middle), and ventral (bottom) views. The numbers correspond to those assigned to discrete landmarks (Supplementary Table 1).