Among the early church fathers, it was noted that the offices of elder and bishop were identical, and weren't differentiated until later, and that plurality of elders was the norm for church government. St. Jerome (347-420) "In Epistle Titus", vol. iv, said, "Elder is identical with bishop, and before parties multiplied under diabolical influence, Churches were governed by a council of elders." This observation was also made by Chrysostom (349-407) in "Homilia i, in Phil. i, 1" and Theodoret (393-457) in "Interpret ad. Phil. iii", 445.
this is an extract from a wikipedia article about Presbyterianism about the office of bishop and elder. Is this claim got any ground and they say there is evidence in the early church father, where is this evidence?