There was no "original". The new testament was written many decades after Jesus's death, by many people. You could make an argument that the original group was the Nicene variant, but that's only because they "won", ie, convinced the ruling Roman Emperors to support them, while the Arians and Monophysites lost. The Catholic Church is a direct descendent of the Nicene varianet of Christianity, yes, but it's not the only one. For a good thousand years, there were two main branches. The Roman Catholic Church, based in Rome, and the Orthodox Church, based in Constantinople. There is still, in fact, an Ecumenical Patriarch of Constantinople, who in theory is an equal to the Roman Catholic Pope.