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Compact Symmetric Objects (CSOs) are compact (<1 kpc), jetted Active GalacticNuclei (AGN), whose jet axes are not aligned close to the line of sight, andwhose observed emission is not predominantly relativistically boosted towardsus. Two classes of CSOs have previously been identified: approximately onefifth are edge-dimmed and designated as CSO 1s, while the rest are edgebrightened and designated as CSO 2s. This paper focuses almost exclusively onCSO 2s. Using complete samples of CSO 2s we present three independent lines ofevidence, based on their relative numbers, redshift distributions, and sizedistributions, which show conclusively that the vast majority (> 99%) of CSO 2sdo not evolve into larger-scale radio sources. These CSO 2s belong to adistinct population of jetted-AGN, which should be characterized as``short-lived'' compared to the classes of larger jetted-AGN, as opposed to``young''. We show that there is a sharp upper cutoff in the CSO 2 sizedistribution at $\approx 500$ pc. The distinct differences between most CSO 2sand other jetted-AGN provides a crucial new time domain window on the formationand evolution of relativistic jets in AGN and the supermassive black holes thatdrive them.

Compact Symmetric Objects -- II Confirmation of a Distinct Population of High-Luminosity Jetted Active Galaxies