Endocranial anatomy of lambeosaurine hadrosaurids (Dinosauria: Ornithischia): a sensorineural perspective on cranial crest function.

Brain and nasal cavity endocasts of four corythosaurian lambeosaurines (Dinosauria: Ornithischia) were investigated to test hypotheses of cranial crest function related to sensorineural systems. Endocasts were generated through computed tomography and three-dimensional rendering and visualization software. The sample comprises a range of ontogenetic stages from the taxa Lambeosaurus, Corythosaurus, and Hypacrosaurus. Results show that the morphology of brain endocasts differs little from that of hadrosaurines. The strikingly convoluted nasal vestibule of Hypacrosaurus altispinus, when interpreted in the context of lambeosaurine phylogeny, suggests selective pressure for nasal cavity function independent from changes in the external shape of the crest and associated visual display function. The plesiomorphically small olfactory bulbs and apparently small olfactory region of the nasal cavity argues against the hypothesis that increased olfactory acuity played a causal role in crest evolution. The elongate cochlea of the inner ear reveals that hearing in lambeosaurines emphasized low frequencies consistent with the hypothesized low-frequency calls made by the crests under the resonation model of crest function. The brain is relatively large in lambeosaurines compared with many other large dinosaurs, and the cerebrum is relatively larger than that of all non-hadrosaurian ornithischians and large theropods, but compares favorably with hadrosaurine hadrosaurids as well as some maniraptoran theropods. It is concluded that the large brains of lambeosaurines are consistent with the range of social behaviors inferred when the crest is interpreted as an intraspecific signaling structure.