No heads were turned. No mouths were left agape. But Saturday was a symbolic day that perhaps best describes where the Vikings were at the end of the 2013 season and where they're presumed to be heading in 2015.

Hundreds of NFL transactions were made Saturday as teams reached their 53-man rosters. The Vikings, like most, pulled no dramatic surprises. But there were three leaguewide transactions that leapt off the page to unite in a sad summarization of the Vikings' quarterback situation only 20 months ago.

In Oakland, Christian Ponder was released. In Buffalo, Matt Cassel was released. In Miami, Josh Freeman was released. And in Tampa, Leslie Frazier suddenly had three timely arguments for an NFL head-coaching mulligan.

In 2013, Ponder, Cassel and Freeman were the Vikings' quarterbacks. They completed fewer than 60 percent of their passes for 18 touchdowns with 19 interceptions and a 5-10-1 record. Not coincidently, that also was Frazier's final season.

Fast forward 20 months and give a belated thanks to the three-headed Pond-el-man quarterbacking monster. Without its distinct shortcomings and the coinciding Upper Midwest death of Frazier's Tampa 2 defense, the Vikings wouldn't have worked so desperately to vet Teddy Bridgewater's qualifications or bucked a trend by hiring Mike Zimmer, a cutting-edge defensive coach.

Compared with 2013, the team that General Manager Rick Spielman finalized Saturday is better coached and more talented and deeper at every position group, except offensive line, where more time is needed to evaluate just what the Vikings have or don't have heading into next Monday's regular-season opener at San Francisco.

Biggest concern: offensive line

Listing the top six concerns on this year's team could look like this: left tackle, left guard, center, right guard, right tackle and all of the above.

If this team doesn't live up to its hype as a surprise playoff pick, chances are the offensive line will be the leader in underperforming. Each player has something to prove that could go either way.

Matt Kalil played poorly last year. Brandon Fusco missed 13 games and has changed positions. John Sullivan hasn't practiced or played in three weeks because of back spasms. Mike Harris is a career tackle playing guard. T.J. Clemmings is a rookie selected on Day 3 of the draft.

How will all of this play out? The temptation based on the preseason is to say better than expected. In fact, Clemmings, the biggest question mark up front, looks stout enough and much more athletic than Phil Loadholt.

But who knows how this unit will play when defenses start game planning against it. All we can say for sure is a promising season filled with the likes of Bridgewater, Adrian Peterson, Mike Wallace, Kyle Rudolph and a top 10-caliber defense ultimately won't be so promising if the offensive line goes splat.

Three other concerns: The starting left cornerback (Terence Newman) turned 37 on Friday. … No one can wrestle the starting strong safety job from Robert Blanton's tentative grip. Again. … Kicker Blair Walsh struggled last year and then missed more field goal attempts than he made this preseason.

Quick hits

Breakout player: Sharrif Floyd, defensive tackle.

Good conditioning, quicker feet and a higher comfort level with the defense have him poised to unleash the kind of interior pass rushing productivity that turns heads nationally. But all praise for Floyd comes with the old "if he stays healthy" disclaimer. A big if at this point.

Team MVP: Bridgewater.

As historically great as he is, Peterson enters his ninth NFL season with all of one playoff victory. Even the year he ran for 2,097 yards and won league MVP, the Vikings didn't win their division.

Expect greatness from Peterson, but team success might come only if Bridgewater, the team's youngest starter at 22, uses the extra attention on Peterson to spot receiving mismatches and then execute explosive pass plays with poise and accuracy, two of his strengths. The only quarterback to do that alongside Peterson consistently was Brett Favre.

That came in 2009, the only year Peterson ever tasted playoff success.

Mark Craig mark.craig@startribune.com