  We use simulations of merging galaxies to explore the sensitivity of the
morphology of tidal tails to variations of the halo mass distributions in the
parent galaxies. Our goal is to constrain the mass of dark halos in well-known
merging pairs. We concentrate on prograde encounters between equal mass
galaxies which represent the best cases for creating tidal tails, but also look
at systems with different relative orientations, orbital energies and mass
ratios. As the mass and extent of the dark halo increase in the model galaxies,
the resulting tidal tails become shorter and less massive, even under the most
favorable conditions for producing these features. Our simulations imply that
the observed merging galaxies with long tidal tails ($\sim 50-100$ kpc) such as
NGC 4038/39 (the Antennae) and NGC 7252 probably have halo:disk+bulge mass
ratios less than 10:1. These results conflict with the favored values of the
dark halo mass of the Milky Way derived from satellite kinematics and the
timing argument which give a halo:disk+bulge mass ratio of $\sim 30:1$.
However, the lower bound of the estimated dark halo mass in the Milky Way (mass
ratio $\sim 10:1$) is still consistent with the inferred tidal tail galaxy
masses. Our results also conflict with the expectations of $\Omega=1$
cosmologies such as CDM which predict much more massive and extended dark
halos.
