User blog comment:Cory Jaynes/Reapers origins/@comment-903543-20110805041231/@comment-190.45.29.236-20110805220508

As Ironreaper said it, Liara explains the existance of other species, as well does the flavor text of some planets with remains of species older than the extinction of the protheans. Besides, as Vigil stated, the Reapers where very thorough with the annihilation of the Protheans. If they came 50.000 years before the extinction of the Protheans, another species was destroyed