Rem, The evidence that I have is as follows:
1. This person is identified as the author by the early church fathers including Polycarp, Hermas, Papias, Irenaeus ( who wrote - And after their(Peter and Paul's) deathMark, the disciple and interpreter of Peter, himself also handed down to us in writing the things preached by Peter), Justin Martyr, Clement of Alexandria, Terullian, Origen, Cyril of Jerusalem, Eusebius, Jerome, and Augustine.
2. He is identified within the Bible itself: He was a Jewish Christian whhose mother, Mary, owned a home in Jerusalem where the earlt church met ( Acts 12:12); He was the cousin of Barnabas ( Col. 4:10);When 1 Peter was written, Mark was with Peter in Rome and regarded as Peter's spiritual son ( 1Peter 5:13)
3. There is evidence within Mark itself to connect this author with Peter such as the inclusion of the unique words "and Peter" ( 16:7) and the close similarity between the broad outline of this Gospel and Peter's sermon detailed in Acts 10.
Joseph,
I respectfully disagree that you have given detailed reasons why you think the Gospel of Mark or Jesus is fictional. You have given nothing more than your opinions and speculations. These are some of the same opnions as expressed by the members of the Jesus seminar, which are long on theory and speculation but short on evidence.
As for Harvard professors I would point you to Harvard Law Professor Simon Greeleaf. He was known as the most prominent professor of evidence in his day and wrote a book on evidence that was quoted by the Supreme court. He studied the evidence to support and deny that Christ was a true historical figure and concluded that he was and became a Christian. ( As cited by Irwin Linton in his book A Lawyer Examines the Bible).
I do not view the differences between the accounts of the colt and the donkey as contradictions. In all of them Jesus enters the city on a colt. Matthew includes a donkey, but that does not contradict the other accounts, it adds to them. For example if four people say that a man was wearing blue pants and one of them adds that he was wearing a red shirt, does that addition contradict the other versions or does it simply add to them another detail? This additional detail could easily have been given by Matthew since he was a disciple and was acutally present when the event happened.
Also, does the addition of the donkey by Matthew defeat that the prophecy was fulfilled? It doesn't. The essense of the prophecy is fulfilled by Jesus, the Messiah, entering Jerusalem on an animal triumphantly. All of which is consistent in the Gospels.
Finally, you are incorrect in your reading. Mark wrote that the disciples fetched a colt, as does Luke. John mentions it as an "ass" and quotes the prophecy as an "ass's colt". But is a baby horse still not a horse? Of course it is. SO if one writer refers to it as a horse and another as a colt aren't they both right?
Joseph, you go to great lengths in your attempt to show apparent contradictions in the Bible? I have asked you before why this is but never received an answer. Of course that is private and if you do not want to answer that is fine. I am just curious where you are coming from. For me, the fact that the Bible was written by over forty men over thousands of years is free from condradiction proves to me that it was an inspired book. By beliefs are intact.