P3.138 Friday, Jan. 6 A tale of two tails: Swimming mechanics in Varanus salvator YOUNG, Bruce A; DUMAIS, Jessica; MCMAHON, Katelyn; BURNELL, Amy L*; Univ. of Massachusetts, Lowell; Univ. of Massachusetts, Lowell; Univ. of Massachusetts, Lowell; Univ. of Massachusetts, Lowell firstname.lastname@example.org
Varanus salvator is a relatively large, semi-aquatic lizard. The tail makes up nearly half of the total body length, supports a low dorsal fin, and, particularly at the proximal base, has robust musculature. Unlike most semi or fully aquatic vertebrates, the tail of the water monitor tapers to a point with no distal expansion for increased surface area. The mass, physiological cross-sectional area of the axial and hypaxial muscle, and lateral projected surface area all decrease along the length of the tail. When swimming these lizards hold their limbs still against the lateral body surface and make limited axial undulations anterior to the pelvis; this is a form of carangiform or sub-carangiform locomotion. Kinematic analysis demonstrated that the undulatory propagation along the tail of V. salvator is similar to what has been described in some anguiliform and other subcarangiform swimmers (e.g., increased amplitude, negative angles of attack, etc.). Applying established equations for undulatory propulsion demonstrates that propulsive force, work, and the slip ratio all decrease along the length of the tail. This creates an unusual situation in which the proximal 1/3 of the tail generates roughly 60% of the propulsive force while the distal 1/3 accounts for less than 15%. A series of experiments involving electromyography, high-speed digital videography, and modeling were undertaken to explore the functional differences between the proximal and distal portions of the tail. In particular, we sought to determine if the distal half of the tail was moving under active muscle control (or through passive coupling with the proximal tail base) and the relationship between expanded lateral surface area and tail length.