  We construct mass models of 28 S0-Sb galaxies. The models have an
axisymmetric stellar component and a NFW dark halo and are constrained by
observed Ks-band photometry and stellar kinematics. The median dark halo virial
mass is 10^12.8 Msun, and the median dark/total mass fraction is 20% within a
sphere of radius r_1/2, the intrinsic half-light radius, and 50% within R_25.
We compare the Tully-Fisher relations of the spirals and S0s in the sample and
find that S0s are 0.5 mag fainter than spirals at Ks-band and 0.2 dex less
massive for a given rotational velocity. We use this result to rule out
scenarios in which spirals are transformed into S0s by processes which truncate
star formation without affecting galaxy dynamics or structure, and raise the
possibility of a break in homology between spirals and S0s.
