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First published online June 6, 2005
Journal of Experimental Biology 208, 2319-2332 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01624

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Cuvier's beaked whale (Ziphius cavirostris) head tissues: physical properties and CT imaging

Melissa S. Soldevilla^1,*, Megan F. McKenna², Sean M. Wiggins¹, Robert E. Shadwick¹, Ted W. Cranford² and John A. Hildebrand¹

¹ Scripps Institution of Oceanography, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0205, USA
² San Diego State University, 5500 Campanile Drive, San Diego, CA 92182, USA

View larger version (51K): [in a new window]   Fig. 1. (A) Reconstructed computer image of a neonate Z. cavirostris head. Dark grey areas show the outer skin layer. The light blue region is bone, i.e. the skull and mandible. The white area is the connective tissue theca that encompasses the melon, seen in yellow. Mandibular fat bodies are also shown in yellow. Colorized CT scans of transverse slices through (B) a posterior region and (D) an anterior region of the head. C and E represent line drawings that diagram the body parts seen in scans B and D, respectively. Abbreviations: b, blubber; ct, connective tissue; ma, maxilla; me, melon; mf, mandibular fat; mn, mandibular bones; mu, muscle. Only interior mandibular fat is represented in these images.

View larger version (117K): [in a new window]   Fig. 2. 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.

View larger version (106K): [in a new window]   Fig. 3. (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.

View larger version (16K): [in a new window]   Fig. 4. Sound speed versus temperature from Ziphius cavirostris head tissues.

View larger version (13K): [in a new window]   Fig. 5. 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.

View larger version (70K): [in a new window]   Fig. 6. 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).

View larger version (21K): [in a new window]   Fig. 7. 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.

View larger version (17K): [in a new window]   Fig. 8. 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).

View larger version (19K): [in a new window]   Fig. 9. 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.

View larger version (20K): [in a new window]   Fig. 10. 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.

View larger version (18K): [in a new window]   Fig. 11. Regression analysis of Hounsfield units versus (A) sound speed and (B) density for Ziphius cavirostris forehead tissues. Best-fit lines are represented by the following equations: sound speed=1.6889HU+1535.9; density=0.001HU+1.0265.