The linear viscoelastic behavior in dynamic shear and tensile creep at temperatures from 30 to 70 degrees C is measured for an styrenebutadiene rubber (SBR) elastomer cured with dicumyl peroxide to crosslinking densities between 0 and 23.5 x 105 mol/cm3. The G, G, and tan isotherms are analyzed by timetemperature superposition (TTS), where the tan master curves are consistent with those of Mancke and Ferry. However, to achieve the TTS in the lightly crosslinked SBR systems, an anomalous vertical shift is required in the narrow temperature region from 10 to 30 degrees C. The vertical shift factor in this temperature region is not the standard ${{\rho _0 T_0 } \mathord{\left/ {\vphantom {{\rho _0 T_0 } {\rho T}}} \right. \kern-\nulldelimiterspace} {\rho T}}$ from rubber elasticity. No anomalous behavior is detected in the equilibrium modulus, which is a linear function of temperature in accordance with the classical theory of rubber elasticity. In contrast to SBR, standard vertical shifts are required to effect TTS for uncrosslinked polybutadiene and an ethylene propylene diene monomer elastomer. (c) 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013