Meeting Abstract

74.3  Saturday, Jan. 5  A Comparative Look at Tail Movement During Narrow Branch Locomotion. CHADWELL, BA*; YOUNG, JW; SHAPIRO, LJ; NEOMED, Rootstown, OH; NEOMED, Rootstown, OH; Univ. of Texas, Austin bchadwell@neomed.edu

Tails have been suggested to act as either counterweights or dynamic stabilizers to maintain balance during locomotion, functions that should be especially important on narrow substrates, e.g. branches. Most tests of these assertions have been based on mathematical modeling, purely morphological studies, or qualitative observation. Few empirical data exist with which to test tail function during narrow branch locomotion. We present kinematic data on tail movements in two primates, squirrel monkeys (Saimiri) and tamarins (Saguinus), during quadrupedal locomotion on a 3.2cm diameter pole. Ongoing studies are focused on describing locomotor tail movements in other arboreal animals as well (e.g., Petaurus). Morphological data suggest that Saguinus has reduced power-grasping abilities relative to Saimiri, perhaps necessitating compensatory means of maintaining balance on narrow substrates. To test this hypothesis, we used video analyses to document tail angular kinematics throughout strides. We predicted that tails used as effective balancing organs, whether as counterweights or dynamic stabilizers, should be held at elevated angles with respect to the substrate, thus maximizing rotational inertia and resistance to movement. Additionally, tails used as dynamic stabilizers should exhibit exaggerated movement over a stride. Controlling for variation in speed and body mass, we found that Saguinus holds the tail at more elevated angles (mean angular position: Saguinus 7.1 deg; Saimiri -15.5 deg; p<0.05) and moves the tail through wider ranges of motion (amplitude: Saguinus 26.1 deg; Saimiri 13.7 deg; p<0.05). These preliminary data suggest that tamarins are more reliant on using their tails as balancing organs. Supported by NSF BCS-1126790 and NSF BCS-0647402.