Hyolingual biomechanics and kinematics in three species of two odontocete genera were investigated to compare adaptations and performance of divergent feeding strategies. Ram and suction feeding are two ends of a continuous spectrum that is poorly-studied in odontocetes. Comparative anatomy identified characters associated with feeding patterns of morphologically dissimilar and evolutionary distant genera. Hyolingual investigations included measurements of hyolingual muscle vectors and hyoid surface area/robustness. ANOVA's revealed Kogia basihyal and thyrohyal surface areas were significantly greater than T. truncatus. However, most predicted muscle tension values were not significantly different between genera. The presence of lateral gape occlusions, broad basihyal and thyrohyals near the caudal oral cavity, and a broad, short tongue were likely responsible for Kogia's effective suction mechanism. These features were absent, or reduced, in T. truncatus. The feeding kinematics of dwarf and pygmy sperm whales (Kogia sima and K. breviceps), and bottlenose dolphins (Tursiops truncatus) were characterized and compared incorporating the Ram-Suction Index (RSI). Mean RSI data support a suction feeding strategy for the phylogenetically basal Kogia (-0.67; S.D.ñ0.29) and a ram feeding strategy for the more-derived Tursiops (0.94; S.D.ñ0.11). Tursiops displayed two ram-based feeding behaviors, closed gape approach, where gape increased near food items, and open gape approach, where gape was at least 50% of maximum in the first video field. Four feeding phases were identified in both odontocetes: preparatory, jaw opening, gular depression, and jaw closing. The mean Kogia feeding cycle duration (470 ms; S.D.ñ139) was significantly shorter (P<0.003) than all Tursiops groups (pooled: 863 ms; S.D.ñ337, closed gape approach: 662 ms; S.D.ñ207, open gape approach: 1211 ms; S.D.ñ207). Kogia mean maximum gape angle (39.8ð; S.D.ñ18.9), mean maximum opening, and closing gape angle velocities (293ð/s; S.D.ñ261 and 223ð/s; S.D.ñ121, respectively) were significantly greater (P<0.005) than pooled Tursiops mean maximum gape angle (24.8ð; S.D.ñ6.6), mean maximum opening and closing gape angle velocities (84ð/s; S.D.ñ56 and 120ð/s; S.D.ñ54, respectively). Negative Kogia RSI values were correlated with increasing maximum hyoid depression and retraction, wide gape angle, and rapid opening gape velocity. Kinematic data support functional hypotheses that odontocetes generate suction by rapid depression of the hyoid and tongue.
| Identifer | oai:union.ndltd.org:TEXASAandM/oai:repository.tamu.edu:1969.1/5868 |
| Date | 17 September 2007 |
| Creators | Bloodworth, Brian Edward |
| Contributors | Marshall, Christopher D., Cowan, Daniel F., Horning, Markus, Packard, Jane M., Tarpley, Raymond J. |
| Publisher | Texas A&M University |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Electronic Thesis, text |
| Format | 3339517 bytes, electronic, application/pdf, born digital |
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