Ziphius cavirostris skull. The concave skull basin where the melon is located is readily apparent. The hollowed mandibles, which house the acoustic fats important to sound reception, are also noted.

(A) Head of a neonate Z. cavirostris. Arrowheads point to transverse slices (A–O) that were taken through the melon. (B) Anterior side of a transverse slice through the melon, which corresponds to slice K, from A. Skin, blubber, connective tissue, muscle and melon tissues are noted. (C) Transverse melon slice K, showing grid-like sampling of tissues into numbered cubes. (D) Transverse CT scan image of slice K. Maxillary and mandibular bones are visible as bright white areas. Between these is the tongue. A blubber sheath can be seen surrounding the animal. The connective tissue, muscle and melon fats can be discerned in the upper portion of the figure. Interior and exterior mandibular fats can be seen inside of and around the mandibular bones. Throat grooves are also visible.

Sound speed versus temperature from Ziphius cavirostris head tissues.

Box and whisker plots of (A) sound speed corrected to 37°C, (B) mass density and (C) CT scan Hounsfield units for various tissue types in the forehead and mandible. The lines of the boxes represent the lower-quartile, median and upper-quartile values. The whiskers extending from each end of the box show the extent of the remaining data. Outliers are represented by + signs beyond the whiskers. The dark blue horizontal lines represent the sound speed (1507 m s^–1), density (1026 kg m^–3) and HU (0), respectively, of seawater at 15°C and 101 kPa.

Sound speed through 13 transverse slices (A–M) of Ziphius cavirostris melon. Slices N and O are not shown in this analysis since they encompass the nasal plugs. The figure shows the anterior face with dorsal side up. The animal's right (R) and left (L) sides are as shown in the figure. The color bar scale represents sound speed values (m s^–1).

Stress–strain curve for a sample of Ziphius cavirostris forehead blubber. The 10 low-stress pulses are visible at the low end of the curve, while the larger curve represents the single high-stress pulse.

Elastic modulus versus stress for tissues from a Ziphius cavirostris forehead and mandible. Blubber, acoustic fats and connective tissues are plotted for each location. Note that values have been averaged across three orientations (anterior–posterior, dorsal–ventral, lateral).

Results of a principal components analysis showing the loadings of each variable for the first two principal components. Density, Hounsfield unit and sound speed are all described primarily by the 1st principal component, while elastic modulus is described by the 2nd principal component.

Scatter plot of 1st and 2nd principal component loadings for each Ziphius cavirostris tissue sample. Lipids, muscle and connective tissue can be distinguished from each other by the first component, while acoustic fats are distinguished from blubber by the second component.