KINEMATICS OF AQUATIC PREY CAPTURE IN THE SNAPPING TURTLE CHELYDRA SERPENTINA

Abstract

The kinematics of feeding on two prey types is studied quantitatively in the common snapping turtle, Chelydra serpentina, to provide a description of prey capture mechanisms and to determine whether kinematic patterns can be altered in response to prey that vary in escape capability. High-speed video recordings of prey capture (200 fields s−1) provide data for field-by-field analysis of 12 kinematic variables characterizing head and neck movement. Feedings on fish were accomplished in 78ms, with peak head extension velocities of 152.5cms−1. Worm feedings lasted 98ms with maximum head extension velocities of 54cms−1. Both univariate and multivariate statistical analyses demonstrate significant differences in kinematic patterns between fish and earthworm feedings: Chelydra serpentina possesses the ability to modulate its kinematic pattern depending on the prey. The pattern of bone movement during the fast opening phase of the gape cycle is similar to that found in ray-finned fishes, lungfishes and aquatic salamanders. However, movements of the cranium and lower jaw during the closing phase are markedly different. Our data show Chelydra to be predominantly a ram-feeder, with any intraoral negative pressures generated during the strike having a negligible effect on the prey, which remains largely stationary relative to a fixed background. Hyoid and esophageal expansion during the closing phase may function to allow a unidirectional flow of water and prey into the mouth until the gape closes and to delay reverse flow until the prey has been trapped inside the mouth. The independent evolutionary acquisition of aquatic feeding in fishes and turtles reveals some kinematic similarities that may be the result of hydrodynamic constraints on aquatic prey capture systems, as well as kinematic differences that result from the fundamentally different morphological design of the prey capture apparatus.