  We explore the possibility of shape transitions in proton-neutron systems
driven by deformation differences between proton and neutron fluids. Within the
framework of the proton-neutron interacting boson model, we show that such
dynamic shape transitions cannot occur in well deformed nuclei but are a
possibility in transitional nuclei. Likely candidates in the Os-Pt isotopes are
discussed and predictions of the model are compared with the existing data.
