  A full understanding of how unusually large "Ultra Diffuse Galaxies" (UDGs)
fit into our conventional understanding of dwarf galaxies remains elusive,
despite the large number of objects identified locally. A natural extension of
UDG research is the study of similar galaxies at higher redshift to establish
how their properties may evolve over time. However, this has been a challenging
task given how severely systematic effects and cosmological surface brightness
dimming inhibit our ability to study low-surface brightness galaxies at
high-$z$. Here, we present an identification of low stellar surface density
galaxies (LDGs), likely the progenitors of local UDGs, at moderate redshift
with deep near-IR observations of the El Gordo cluster at $z = 0.87$ with JWST.
By stacking 8 NIRCAM filters, we are able to achieve an apparent surface
brightness sensitivity of $24.59$ mag arcsec$^{-2}$, faint enough to be
complete to the bright end of the LDG population. Our analysis identifies
significant differences between this population and local UDGs, such as their
color and size distributions, which suggest that UDG progenitors are bluer and
more extended at high-$z$ than at $z = 0$. This suggests that multiple
mechanisms are responsible for UDG formation and that prolonged transformation
of cluster dwarfs is not a primary UDG formation mechanism at high-$z$.
Furthermore, we find a slight overabundance of LDGs in El Gordo, and, in
contrast to findings in local clusters, our analysis does not show a deficit of
LDGs in the center of El Gordo, implying that tidal destruction of LDGs is
significant between $z = 0.87$ and $z = 0$.
