  Today, Pluto and Eris are the largest and most massive Trans-Neptunian
Objects respectively. They are believed to be the last remnants of a population
of planetesimals that has been reduced by >99% since the time of its formation.
This reduction implies a primordial population of hundreds or thousands of
Pluto-mass objects, and a mass-number distribution that could have extended to
hundreds of Lunas, dozens of Mars, and several Earths. Such lost protoplanets
would have left signatures in the dynamics of the present-day Trans-Neptunian
Populations, and we statistically limit their primordial number by considering
the survival of ultra-wide binary TNOs, the Cold Classical Kuiper belt, and the
resonant population. We find that if the primordial mass-number distribution
extended to masses greater than Pluto (~1e-3 Earth masses), it must have turned
downwards to be no more top-heavy than roughly equal mass per log size, a
significant deviation from the distribution observed between 1e-5 and 1e-3
Earth masses. We compare these limits to the predicted mass-number distribution
of various planetesimal and proto-planet growth models. The limits derived here
provide a test for future models of planetesimal formation.
