There were yet earlier traditions about Jesus that did not speak of him as the son of God from eternity past or from his miraculous birth or from the time he began his ministry. In these, probably the oldest, Christian traditions, Jesus became the Son of God when God raised him from dead. It was then that God showered special favor on the man Jesus, calling him the son, the messiah, the Lord. Even though this view is not precisely that of Paul, it is found in an ancient creed (that is, a preliterary tradition) that Paul quotes a the beginning of his letter to the Romans, where he speaks of Christ as God's "son who was descended from David according to the flesh and designated Son of God in power according to the Spirit of holiness at his resurrection. . . . It is, in other words, a very ancient tradition that predates Paul's writings. (p.111)Ehrman raises this point as part of an argument assigning an early date to the traditions underlying Acts, but it seems to me that its mythicist implications are fairly obvious and might have been addressed.
Why would the earliest Christians, presumably the ones that Paul persecuted before his conversion, believe that Jesus became the messiah only upon his resurrection if they understood him to have been anything like the wonder working messianic claimant that we find in the gospels? Had their been any known traditions concerning a Galilean teacher and healer, wouldn't the early Christians have believed that Jesus was the messiah and the Son of God throughout his entire earthly ministry? Doesn't the fact that the earliest Christians thought of Jesus as becoming the anointed one only upon his resurrection at least suggest that the stories about the activities of the earthly Jesus were added sometime later.