The nucleus 158Yb has a transition from quasivibrational structure at low spins and temperatures to quasirotational structure at high spins and moderate temperatures. Thermal shape fluctuations produce fluctuations in and ω. However, these fluctuations do not eliminate the structural transition. The standard deviations in and ω decrease at moderate temperatures. Consequently, thermal shape fluctuations produce minimal dispersion in E2 gamma energies, for moderate temperatures and high spins.