  The data available for short-lived $p$-nuclides are used in an open nonlinear
model of the chemical evolution of the Galaxy in order to discuss the origin of
extinct radionuclides, the stellar sources of $p$-nuclides, and the chronology
of solar system formation. It is concluded that the observed abundances of
$^{97}$Tc, $^{98}$Tc, $^{92}$Nb, and $^{146}$Sm in the early solar system are
consistent with nucleosynthesis in type II supernovae during continuous
chemical evolution of the Galaxy and a subsequent short isolation of the
presolar molecular cloud from fresh nucleosynthetic inputs. However, further
work on supernova models is needed before $p$-radionuclides will comprise
reliable cosmochronometers. Despite these limitations, we argue that niobium-92
can be used to test whether the {\it rp}-process contributed to the synthesis
of light {\it p}-nuclides in the Mo-Ru region.
