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The captured images were used to assess the axial region in which lateral flexion was
occurring. Figure 3a shows a superimposition of a full skeleton of
Inia geoffrensis
(drawn
after Flower, 1869, and de Miranda-Ribeiro, 1943) over an illustration of the captive dolphin
from the Pittsburgh Zoo. This superimposition shows that dorsal ridge and peduncle are post-
thoracic regions, corresponding to the ―torso‖ region as defined by Buchholtz (2001). Herein,
we refer to the region of the dorsal ridge, which include the lumbar and parts of the adjacent
vertebrae, as the anterior torso. The peduncle, which includes only caudal vertebrae,
corresponds to the posterior torso. The anterior torso is the point of greatest dorsoventral
bending during swimming in
Inia
, as is also likely true for many extinct cetaceans
(Buchholtz, 2001). The lateral mobility
in the two parts of the torso is a focus in this
chapter.
Figure 3. a) Superimposition of the skeleton of
Inia geoffrensis
(drawn after Flower, 1869; and de
Miranda-Ribeiro, 1943) over an illustration of the captive dolphin from the Pittsburgh zoo (drawn after
a photograph). b) Dorsal still image from video tape of the captive river dolphin, with lines
approximating the thorax (A-B, used as midline for calculating lateral flexibility) orientation of neck
(based on a line drawn through the rostrum - a-b) and torso (c-d and e-f). Angles of these regions are
indicated. The thorax line was identified by drawing a line transecting the roots of the two pectoral
flippers and then drawing A-B perpendicular to this line. Angles: 1 = cervical; 2 = anterior torso; 3 =
posterior torso; 4 = total torso angle (anterior + posterior). (© 2008, Timothy D. Smith).
The presumptive cervical and torso regions were assessed relative to a thoracic region
(see below) in which lateral flexibility is presumed to be more constrained due to costal
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