Patterns of body temperatures: Is lizard thermoregulation chaotic?

We surveyed body temperature (Tb) fluctuations of 23 species of thermoregulating lizards (9 families, 305 individuals) for pattern similarities. Here we report that the Tb time-series patterns of all species and almost all individuals met both qualitative criteria and quantitative criteria (positive Lyapunov exponent and capacity and/or correlation dimensions less than 5, and Hurst exponent not equal to 0.5) for deterministic chaos. Chaotic thermoregulation appears controlled, but at unpredictable times becomes disturbed and exhibits nonlinear behaviors before returning to control. This chaotic pattern of regulation is common to sufficiently diverse species to suggest that it is likely a primitive lacertilian, and perhaps reptilian, physiological characteristic.