Why is there a presumption that these bones are "ancient"? They could have been the remains of people who lived only a few centuries ago, and were of a stature that is simply at the edge of the extremes of humans who are alive today. There are plenty of modern earthlings who are over 7 feet tall.
Here is a site with numerous such accounts:
http://s8int.com/giants19.html
There is one consistent thread that runs through all of them: None of the skeletons exist today, available for study. Anybody think that sounds odd? Very few were actually measured.