A neurological method for assessment of nasal cavity homologies in extant archosaurs is extended to lambeosaurine hadrosaurids (Dinosauria: Ornithischia) to test functional hypotheses associated with their hypertrophied nasal passages and highly derived cranial crests. The olfactory system and associated cranial nerve pathways that have consistent relationships to soft tissue divisions of the nasal cavity are reconstructed in lambeosaurines on the basis of new paleoneurological data and a comparative phylogenetic approach. The new model of the lambeosaurine olfactory system and nasal cavity shows that a significant portion of nasal cavity proper was located outside the crest cavities and that the primary olfactory region was located rostromedial to the orbits.
All available data indicate that the evolutionary hypertrophy of the nasal cavity occurred predominantly within the non-olfactory nasal vestibule, and that crest development was not causally associated with olfaction. The high level of interspecific and ontogenetic variation in crest shape and nasal vestibule development in lambeosaurine dinosaurs is most consistent with proposed behavioral functions, notably acoustic resonance for intraspecific communication. Despite significant modification to the nasal cavity within Archosauria and its extreme hypertrophy and supraorbital development in Lambeosaurinae, the neural olfactory system and the olfactory region of the nasal cavity proper retain their plesiomorphic positions and associations, suggesting that this system is highly conserved in vertebrate evolution.