  The Hubble Ultra Deep Field source JD2 presented in Mobasher et al. (2005) is
an unusual galaxy that is very faint at all wavelengths shortward of 1.1
micron. Photometric redshift fits to data at 0.4 to 8 microns yield a
significant probability that it is an extremely massive galaxy at z~6.5. In
this paper we present new photometry at 16 microns and 22 micron from Spitzer
Infrared Spectrograph (IRS) peak-up imaging of the Great Observatories Origins
Deep Survey (GOODS) fields. We find that the spectral energy distribution shows
a factor of ~4 rise in flux density between the 16 micron and 22 micron
bandpass which is most likely due to the entrance of polycyclic aromatic
hydrocarbon emission features into the 22 micron and 24 micron passbands. The
flux ratio between these bandpasses can be best fit by a z~1.7 luminous
infrared galaxy with a bolometric luminosity of (2-6)\times10^{11} L_sun
corresponding to a star-formation rate of 80 M_sun/yr. The predicted flux
density values at other longer wavelengths are below the detection limits of
current instrumentation but such sources could potentially be detected in
lensed submillimeter surveys. Re-evaluation of the optical/near-infrared
photometry continues to favor z>6 photometric redshift solutions, but we argue
that the consistency of the multiwavelength parameters of this galaxy with
other dusty starbursts favor the z~2 mid-infrared photometric redshift. The
data presented here provide evidence that optically undetected near-infrared
sources which are detected at 24 microns are most likely dusty, starburst
galaxies at a redshift of z~2 with stellar masses >10^{10} M_sun.
