Roston, RA; Roth, VL, Different developmental transformations underly blowhole orientation in a toothed whale (Odontoceti: Stenella attenuata) and a baleen whale (Mysticeti: Balaenoptera physalus),
The FASEB Journal, vol. 34 no. S1
(April, 2020),
pp. 1-1, Wiley [doi] .
(last updated on 2024/08/25)
Abstract:
Although the external bony nares have become posteriorly repositioned in the evolution of numerous groups of mammals (e.g. elephants, tapirs), reorientation of the nasal passage away from the anteroposterior axis has evolved rarely. In cetacean (whale, dolphin, porpoise) evolution, dorsoventral reorientation of the nasal passage along with extreme posteriad repositioning of the nares formed a “blowhole.” Despite the presence of a blowhole at birth, early cetacean fetuses exhibit head morphologies that resemble those of other mammals. Two distinct but non‐competing developmental models have been proposed for how the nasal passage reorients into a blowhole. In one model, which focused on external changes in the whole body, nasal passage reorientation was described in terms of dorsad rotation of the head during prenatal growth (Pilleri and Wandeler, 1962). A second, focusing on the nasal skull, noted that the nasal passage itself changes orientation relative to the palate and longitudinal axis of the skull (Klima, 1995, 1999). To integrate and revise these models, we used photos and CT scans of fetal growth series to characterize morphological, allometric, and angular changes within the head in representatives of the two extant cetacean suborders: a toothed whale, the pantropical spotted dolphin (Odontoceti: Stenella attenuata), and a baleen whale, the fin whale (Mysticeti: Balaenoptera physalus). In both fetal series, the angle between the nasal passage and the sagittal axis of the foramen magnum decreased with age, but this trend accompanied different morphological changes. In S. attenuata, the angle between the palate and basicranium flattened in association with facial lordosis and basicranial retroflexion in the region of the presphenoid. Basicranial retroflexion was not observed in B. physalus; rather, alignment of the nasal passage and the sagittal axis of foramen magnum accompanied anteriad tilting of the occipital bone. With these results, we propose a new developmental model, differing in its specifics for a toothed and a baleen whale, for the reorientations that produce the blowhole.