Abstract: In terrestrial mammals, the respiratory turbinate bones within the nasal cavity are employed to conserve heat and water. In order to investigate whether environmental temperature affects respiratory turbinate structure in phocids, we used micro-computed tomography to compare maxilloturbinate bone morphology in polar seals, grey seals and monk seals. The maxilloturbinates of polar seals have much higher surface areas than those of monk seals, the result of the polar seals having more densely packed, complex turbinates within larger nasal cavities. Grey seals were intermediate; a juvenile of this species proved to have more densely packed maxilloturbinates with shorter branch lengths than a conspecific adult. Fractal dimension in the densest part of the maxilloturbinate mass was very close to 2 in all seals, indicating that these convoluted bones evenly fill the available space. The much more elaborate maxilloturbinate systems in polar seals, compared with monk seals, are consistent with a greater need to limit respiratory heat loss.