“Birds and crocodiles show radically different patterns of braindevelopment, and itis of interest to compare these to determine the pattern of brain growth expectedin dinosaurs. Here we provide atlases of 3D brain (endocast) reconstructions forAlligator mississippiensis(alligator) andStruthio camelus(ostrich) through ontog-eny, prepared as digital restorations from CT scans of stained head and dry skullspecimens. Our morphometric analysis confirms that ostrich brains do not changesignificantly in shape during postnatal growth, whereas alligator brains unfoldfrom a cramped bird-like shape in the hatchling to an elongate, straight structurein the adult. We confirm that birds exhibit paedomorphic dinosaur endocranialtraits such as retaining an enlarged and compact brain shape in the adult, whereascrocodiles show peramorphic traits where the brain elongates with growth as theskull elongates. These atlases of ontogenetic stages of modern bird and crocodilianendocrania provide a basis for comparison of non-avian dinosaur endocasts andconsideration of the divergence of the“avian”and“crocodilian”modes of braindevelopment and heterochronic change on phylogenies.”
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