Recently, the radio show "Unbelievable" aired a debate between noted New Testament scholars Bart Ehrman and Richard Bauckham. The debate centered around Ehrman's new book "Jesus Before the Gospels" where Ehrman contends that the stories about Jesus were circulated, altered, and invented by the followers of Jesus before they were written down. Bauckham, provides a counter-argument, where, in his book "Jesus and the Eyewitnesses," he has argued that the Gospels were written within "living memory" of those eyewitnesses of Jesus' ministry and these Gospels are based upon this testimony.
During this spirited discussion Ehrman mentions the second century Church figure Justin Martyr (140's CE) who makes reference throughout his writings to the "memoirs of the apostles." In regard to this, at 48:43, Ehrman states that "he doesn't call them by our Gospels. . . the only memoir he names is the memoirs of Peter. . . he's talking about the Gospel of Peter."
The reference that Ehrman is referring to is Justin Martyr's comments in his Dialogue with Trypho;
“And when it is said that He changed the name of one of the apostles to Peter; and when it is written in the memoirs of Him that this so happened, as well as that He changed the names of other two brothers, the sons of Zebedee, to Boanerges, which means sons of thunder. . ." (Dia. 106; ANF)
Justin is referring to the memoirs of Peter and he is loosely quoting an incident recorded in this "memoir." That Jesus changed the name of an apostle to Peter and the names of two others to "Boanerges." In all of the Gospels, this account can only be found in the Gospel of Mark at 3:16-17;
"He appointed the twelve: Simon (to whom he gave the name Peter); James the son of Zebedee and John the brother of James (to whom he gave the name Boanerges, that is, Sons of Thunder);" (ESV)
No where in the Gospel of Peter is this account of the naming of Peter and the sons of Zebedee mentioned (Hill, 133-134). Therefore, contrary to Ehrman's claims, Justin Martyr can only be referring to the Gospel of Mark and here he connects it to Peter, independently verifying Papias' famous comments on the origins of Mark's Gospel;
"And the Elder used to say this: 'Mark, having become Peter's interpreter, wrote down accurately everything he remembered, though not in order, of the things either said or done by Christ. For he neither heard the Lord nor followed him, but afterward, as I said, followed Peter, who adapted his teachings as needed but had no intention of giving an ordered account of the Lord's sayings. Consequently Mark did nothing wrong in writing down some things as he remembered them, for he made it his one concern not omit anything which he heard or to make any false statement in them." (Eusebius Hist. eccl. 3.39; Holmes, 569)
Here are at least two independent sources, one from the late first century (Papias) and one from mid second century (Justin Martyr) that point to a common understanding in the early Church; that the Gospel of Mark was sourced in the testimony of the apostle Peter.
Hill, C. E. Who Chose the Gospels: Probing the Great Gospel Conspiracy. New York: Oxford University Press, 2010.
Holmes, Michael W., ed. The Apostolic Fathers: Greek texts and English translations. Grand Rapids: Baker Books, 1999.