You expect a zone blocking team to have relatively light (for 300 pound men) linemen who also have some mobility. Given that the Falcons have an offense run by notorious ZBS enthusiast Kyle Shanahan, you won't be stunned to learn they have the lightest front in the entire NFL.
At the bottom are the Atlanta Falcons, even after adding some size earlier in the offseason. The Atlanta offensive line will now feature Andy Levitre and Alex Mack in the starting group, taking over for Mike Person and Joe Hawley. That upped the average from 301.2 pounds to 304.4 pounds, but wasn't enough to take the title of "lightest offensive line" away.
As we've seen again and again, raw poundage doesn't really matter as much as skill, especially in the context of this blocking scheme. The Falcons were excellent at run blocking for large swaths of 2015 and at least decent in pass protection, with the addition of Alex Mack probably serving to upgrade both. With Jake Matthews, Mack, and Ryan Schraeder, plus a couple of decent (?) guards, this should be one of the better units in the NFL.
So remember: Size doesn't always matter!