Mark 16:9-20 has been called a later addition to the Gospel of Mark by most New Testament scholars in the past century. The main reason for doubting the authenticity of the ending is that it does not appear in some of the oldest existing witnesses, and it is reported to be absent from many others in ancient times by early writers of the Church.... See more

Bruce Metzger, A Textual Commentary on the Greek New Testament (Stuttgart, 1971), pages 122-126.

16:9-20 The Ending(s) of Mark. Four endings of the Gospel according to Mark are current in the manuscripts. (1) The last twelve verses of the commonly received text of Mark are absent from the two oldest Greek manuscripts (א and B), from the Old Latin... See more

The longer ending (3), though current in a variety of witnesses, some of them ancient, must also be judged by internal evidence to be secondary. (a) The vocabulary and style of verses 9-20 are non-Markan. (e.g. απιστεω, βλαπτω, βεβαιοω, επακολουθεω, θεαομαι, μετα ταυτα, πορευομαι, συνεργεω, υστερον are found nowhere else in Mark; and θανασιμον and... See more