  We compare the surface brightness-inclination relation for a sample of COSMOS
pure disk galaxies at z~0.7 with an artificially redshifted sample of SDSS
disks well matched to the COSMOS sample in terms of rest-frame photometry and
morphology, as well as their selection and analysis. The offset between the
average surface brightness of face-on and edge-on disks in the redshifted SDSS
sample matches that predicted by measurements of the optical depth of galactic
disks in the nearby universe. In contrast, large disks at z~0.7 have a
virtually flat surface brightness-inclination relation, suggesting that they
are more opaque than their local counterparts. This could be explained by
either an increased amount of optically thick material in disks at higher
redshift, or a different spatial distribution of the dust.
