Fig 1.
CT-based three-dimensional reconstructions of a toothed whale and baleen whale, right lateral view.
Top: Stenella attenuata (USNM 504048). Bottom: Balaenoptera acutorostrata, juvenile specimen not part of this study. The tympanoperiotic complex houses the middle and inner ear structures, and is highlighted in yellow. The insert images are photographs of prepared tympanoperiotic complexes from mature individuals: B. bonarensis (USNM 504955) and S. attenuata (USNM 487880). The tympanic aperture is indicated by the blue arrow and the acoustic funnel is illustrated by the pink cone. Scale bar = 2 cm.
Table 1.
Fetal cetacean specimens used in this study.
Fig 2.
Three-dimensional CT reconstructions illustrating the ontogenetic development of the ears in cetaceans.
The tympanoperiotic complex is highlighted in yellow and the right lateral view is shown. Some parts of the skull were digitally removed to expose the ears. The scale bar represents 1 cm for S. attenuata (a-d) and 2 cm for B. physalus (e-h) except for the enlarged inserts in (a) and (e), which are twice the size of the corresponding image. The insert in (a) is a flipped image of the left side, in which the goniale is more distinct compared to the right side. Specimens featured in each panel are as follows: a) USNM 504373; b) USNM 504022; c) USNM 504052; d) USNM 504008; e) USNM 301532; f) USNM 267672; g) USNM 268884; h) USNM 260585. Abbreviations: a, accessory ossicle; g, goniale; m, malleus; p, periotic; s, sigmoid process; t, tympanic. The V-shaped malleus-goniale complex is illustrated by the pink dashed line.
Fig 3.
Phylogeny of extant and fossil cetaceans examined in this study.
Zygorhiza, select extinct crown cetaceans, and odontocetes have tympanic bullae whose main axes converge anteriorly. In contrast, the clade Balaenopteroidea possess tympanic bullae whose main axes are parallel to each other and the skull, correlating with a recently described lateral sound reception pathway, evident at least in balaenopterids. Phylogeny based on [54].