The Miami Dolphins are the darlings of the offseason. They entered free agency with more than $40 million of cap room and cleaned up by signing the best receiver on the market (Mike Wallace), the top-rated linebacker (Dannell Ellerbe), a pass-catching tight end (Dustin Keller), another athletic linebacker (Philip Wheeler), and kept their own starting players (Brian Hartline, Randy Starks, Chris Clemons).

On paper, the Dolphins look like a clear playoff contender and the only legitimate challenger to the New England Patriots in the AFC East. The sky could be the limit for Miami this season and beyond.

But there is one catch for the Dolphins: None of this is possible unless second-year quarterback Ryan Tannehill takes the next step.

The Dolphins proceeded this offseason with full confidence that Tannehill is a franchise quarterback. It’s a calculated risk after Tannehill had a promising rookie season where his stats didn't necessarily stand out. He threw for 3,294 yards, 12 touchdowns, 13 interceptions and made his share of rookie mistakes.

However, Miami believes Tannehill showed enough flashes of brilliance to go all-in with him. He played winning football most weeks, and led the Dolphins to a better-than-expected 7-9 record.

There is no time for Tannehill to be a one-hit wonder or have a sophomore slump in 2013. A majority of Miami’s moves in free agency were about making Tannehill a better quarterback.

“Ryan has got 35, 36 games under his belt as starting quarterback combined from a college and pro career, and you would normally like to have 35 games under your belt as a graduating senior,” Dolphins general manager Jeff Ireland said recently. “So I think that there is a bunch of upside left in Ryan’s potential, and I like what I see so far. I love his intangible makeup, I love his athletic skill set. We have a long way to go, he knows that, but he can get a lot better, I am very confident in that.”

The Dolphins committed $30 million guaranteed to get Tannehill a legitimate deep threat and No. 1 receiver in Wallace. Despite Tannehill's strong arm, Miami was limited with the deep ball last season because of a poor supporting cast. He completed only 14 passes of more than 20 yards last season. Wallace has elite speed and should be able to change that.

Miami also snagged Keller from the rival New York Jets, and former St. Louis Rams receiver Brandon Gibson. Keller is the safety valve Miami lacked at tight end, and Gibson brings another weapon to add to a strong group of receivers that already includes Wallace, Hartline and Davone Bess.

The Dolphins learned when you have a potential franchise quarterback, it's easier to recruit free agents. Gibson, Keller and Wallace all cited Tannehill as one of the key reasons they signed with Miami.

“I watch tons of film and I really think he’s going to be one of the better young quarterbacks in the NFL,” Gibson said. “He’s got a big arm, and he’s very intelligent and a very good athlete, and I think that can go a long ways.”

Keller played with embattled quarterback Mark Sanchez in New York for four seasons. Keller leaves the Jets for a quarterback in Miami with a much higher ceiling.

“I’m very impressed with him. I like his game a lot,” Keller said of Tannehill. “I think now you put a Mike Wallace on the team, re-sign Brian Hartline, I love Davone Bess in the slot. You’ve got Charles Clay there working at tight end, too. I think there’s a lot people that they’re going to help him thrive this year, and I’m just happy to be one of the pieces.”

Tannehill is significantly ahead of the curve. The Dolphins' initial plan last season was to let Tannehill sit while Matt Moore or David Garrard ran the team. Instead, Tannehill took advantage of injuries and opportunity and started all 16 games.

In fact, Tannehill’s Total Quarterback Rating, which measures a player's complete performance, was better last season than other big-name quarterbacks such as Joe Flacco, Jay Cutler, Andy Dalton and Sam Bradford. The Dolphins believe Tannehill is just getting started.

Tannehill also flew under the radar last season with a potentially special 2012 quarterback class. Andrew Luck of the Indianapolis Colts, Robert Griffin III of the Washington Redskins and Russell Wilson of the Seattle Seahawks all shared the spotlight while leading their teams to the playoffs. Tannehill was the only rookie of the four not to lead his team to the playoffs, but those expectations will rise for Miami next season.

"We're looking for improvement from him. There's no question about it," Dolphins coach Joe Philbin said at the NFL’s owners meetings. “Part of it’s the decision-making that we think is so important. Part of it’s accuracy. Part of it’s play-making ability at critical times in the course of a game. While we think he made some really nice strides in his first year, there’s still a long way to go, and he’s well aware of that.”

The 2013 Dolphins will be Tannehill’s team, and certainly Tannehill’s offense.

An important part of Tannehill’s sophomore season is that he must take more of a leadership role. The Dolphins are a young team that lost a lot of leadership this offseason. Left tackle Jake Long and running back Reggie Bush bolted in free agency, and linebacker Karlos Dansby was released.

Tannehill will lead one of the youngest teams in the NFL next season. He doesn't get the publicity of fellow draft mates Luck, Wilson and RG III, but he will be just as important to the success of his team.