Anatomical and Volumetric Description of the Baird's Beaked Whale (Berardius bairdii) Brain from Magnetic Resonance Imaging.

INTRODUCTION

Baird's beaked whale, a member of the family Ziphiidae, is one of the largest odontocetes, second only to the sperm whale in body mass. The species is known for its exceptional diving abilities, but this behavior makes it difficult to observe in its natural habitat and has contributed to major gaps in our understanding of its biology, including its neuroanatomy. This study provides a detailed anatomical and quantitative description of the Baird's beaked whale brain.

METHODS

The brain was examined using magnetic resonance imaging. External and internal neuroanatomical features were described, including sulcal and gyral patterns. Quantitative measurements were obtained for the cerebral cortex, amygdala, hippocampus, ventricular system, superior and inferior colliculi, cerebellum, the midsagittal cross-sectional area of the corpus callosum, the gyrification index, and the encephalization quotient.

RESULTS

The Baird's beaked whale brain shows an organization typical of odontocetes, including a large and highly gyrencephalic neocortex. The encephalization quotient and relative cerebellar volume are lower than those reported for delphinids, consistent with findings in other deep-diving cetaceans.

CONCLUSION

These neuroanatomical differences may reflect energy allocation strategies related to diving behavior and body size. By placing these traits within a broader mammalian comparative framework, this study contributes to our understanding of how ecological pressures may shape brain evolution, particularly in rarely studied cetacean lineages such as the Ziphiidae.