  We report the identification of 19 presolar oxide grains from the Orgueil CI
meteorite with substantial enrichments in $^{54}$Cr, with $^{54}$Cr/$^{52}$Cr
ratios ranging from 1.2 to 56 times the solar value. The most enriched grains
also exhibit enrichments at mass 50, most likely due in part to $^{50}$Ti, but
close-to-normal or depleted $^{53}$Cr/$^{52}$Cr ratios. There is a strong
inverse relationship between $^{54}$Cr enrichment and grain size; the most
extreme grains are all <80 nm in diameter. Comparison of the isotopic data with
predictions of nucleosynthesis calculations indicate that these grains most
likely originated in either rare, high-density Type Ia supernovae (SNIa), or in
electron-capture supernovae (ECSN) which may occur as the end stage of
evolution for stars of mass 8-10 M$_\odot$. This is the first evidence for
preserved presolar grains from either type of supernova. An ECSN origin is
attractive since these likely occur much more frequently than high-density
SNIa, and their evolutionary timescales ($\sim$20 Myr) are comparable to those
of molecular clouds. Self-pollution of the Sun's parent cloud from an ECSN may
explain the heterogeneous distribution of n-rich isotopic anomalies in
planetary materials, including a recently reported dichotomy in Mo isotopes in
the solar system. The stellar origins of three grains with solar
$^{54}$Cr/$^{52}$Cr, but anomalies in $^{50}$Cr or $^{53}$Cr, as well as of a
grain enriched in $^{57}$Fe, are unclear.
