TESTS OF 2 HYPOTHESES FOR THE ORIGIN OF THE CROTALINE RATTLE

We suggest that the capability to retain terminal scale (here renamed sclerophymal) exuviae that were mobile, i.e., origin of the protorattl e, was contingent on prior evolution of longitudinal bilobing of the s clerophyma. Two hypotheses for initial functional advantage of such bi lobing are tested: the luring effectiveness hypothesis based on putati vely greater visual attractiveness during caudal luring, and one versi on of the dual contact hypothesis based on putatively greater sound in tensity and/ or greater audiospectral equitability during tail vibrati on, Simulated caudal luring that included a bilobed sclerophyma was no t more attractive to fence lizards than luring with a conical scleroph yma. Sound intensity produced from mechanically vibrated models of bil obed sclerophymae was lower than sound intensity from other types of s clerophymae, whereas broad-bandedness of the sound was similar to that of other types. In the absence of support for either hypothesis, we d iscuss possibilities for future research, particularly the need to det ermine the form of the relationship between sound intensity and the fo rce exerted by the sclerophyma.