MOBILITY OF THE AXIAL REGIONS IN A CAPTIVE AMAZON RIVER DOLPHIN (INIA GEOFFRENSIS) - Biology, Evolution and Conservation of River Dolphins Within South America and Asia - page 76

Table 1. Observed Ranges of Lateral Flexibility of Axial Regions (in degrees).
Activity Cervical 1 Anterior torso Posterior torso Total lateral flexibility 2
Training 5.7-80.1 32.2-96.9 42-124.8 137.3-314.7
Feeding 14.5-83.8 40-52.4 60.8-95.6 148.7-158.0
All 5.7-83.8 32.2-96.9 42-124.8 137.3-314.7
1 for definitions of angles see text and figure 2b. 2 includes only observations where all three regions
were quantified in the same still image.
The most acute torso angles were measured from training sessions (Table 1). In one
trained behavior, this dolphin touched his rostrum to his tail (Figures. 4a, b). The most acute
cervical angle was measured from the feeding-only session, almost reaching a right angle
relative to the thorax. It is noteworthy that the feeding-only sessions resulted in few
measurement opportunities because the dolphin was chasing live fish. Therefore, in many
instances he was positioned outside of the horizontal plane. Archived photographs of this
dolphin chasing trout suggest he would capture fish using lateral flexion in all axial regions
(Figure 5).
Figure 5. Photographs (a-d) of the captive river dolphin showing lateral flexion in the neck and torso
during the pursuit of live trout (photographs by TD Smith).
These measurements are the first attempt to quantify lateral axial mobility in dolphins.
The interpretation of regional mobility is made with caution, as it is inferred from skeletal
proportions in reference to the external anatomy. Skeletal proportions do not account for