In an article entitled The “Strange” Ending of the Gospel of Mark, the author claims that Mark 16:9-19 is clearly forged:

Even though this ending is patently false, people loved it and to this day conservative Christians regularly denounce “liberal” scholars who point out this forgery…

The evidence is clear. This ending is not found in our earliest and most reliable Greek copies of Mark.

His evidence is as follows:

According to Bruce Metzger, “Clement of Alexandria and Origen [early third century] show no knowledge of the existence of these verses; furthermore Eusebius and Jerome attest that the passage was absent from almost all Greek copies of Mark known to them.”

Without getting into the fact that people like to overstate their case (really, the evidence is “clear”, the ending is “patently false”?), the evidence itself seems to be biased. No one denies that the earliest physical writings that we have do not contain those specific verses, but the fact is that the earliest manuscripts we have all are of an Alexandrian bias. As I wrote before:

Why do we even have these early Christian documents? Because they primarily were Alexandrian in origin (coincidently this gives those who argue in favor of accuracy in “earlier” manuscripts an Alexandrian bias)…

The texts that remain do so against nature. All we have is a fragmented look into the past by documents lucky enough to be located in ideal locations and surviving two thousand years of man’s destruction.

I also quote Ehrman to make this point:

As noted earlier, papyrus MSS survive only when protected from moisture – when placed in protective caves, jars, or buildings, or when buried in the soil of virtually rain-free regions of Egypt, Palestine, or Mesopotamia (though papyri must neither be too near the surface nor so deeply buried as to be affected by a rising water table).
[Bart Ehrman, The Text of the New Testament in Contemporary Research]

This brings us back to the reliability of Alexandrian texts. One website categorizes the opinions of the various Church Fathers on the endings of Mark. He, interestingly enough, categorizes the Church Fathers as East and West. The chart is telling:

So, the West seems to have preferred the longer ending while the East seems to have rejected it. And what documents do we have that survived? …the ones in the dry climate. This leads the author of the original article to claim the ending of Mark is a “clear” forgery. The evidence is not so clear.