The NCAA Tournament is known for madness, but the past weekend was something else.

There were buzzer-beaters galore, including a half-court heave by Northern Iowa's Paul Jesperson that ended Texas' season late Friday night. That shot set a record, giving double-digit seeds 10 victories in the 32 games of the first round, eclipsing the high of nine victories set in 2001 and 2012.One of those double-digit seeds that claimed a victory was No. 15 Middle Tennessee State, which never trailed on the way to a nine-point win over No. 2 Michigan State, sparking debate whether it was the greatest tournament upset off all time.And the drama didn't end there, reaching peak levels again Sunday. Notre Dame needed a late tip-in by Rex Pflueger to nip Stephen F. Austin, and Wisconsin's Bronson Koenig shocked Xavier with a step-back corner three at the buzzer to send the No. 7 Badgers past the No. 2 Musketeers to the East Regional.Those finishes paled in comparison to another wacky finish involving Northern Iowa. The Panthers led Texas A&M, 69-57, with 44.3 seconds left - and lost in double overtime. The Aggies' comeback from 12 points down with less than a minute left is the largest last-minute deficit overcome to win - not in tournament history, college basketball history.The first and second rounds lived up to the March Madness moniker and have set a high bar for the rest of the tournament.For all the upsets, wild finishes and excitement, though, the field for the Sweet 16 isn't all that surprising if you strip away the seedings. Each of the remaining teams is either a perennial contender (Gonzaga) or from a major conference. Also, if you look back to November most of these squads were expected to play into the second weekend.Of the 16 teams still standing, 12 were ranked in the top 20 of The Associated Press preseason top 25. Oregon was just outside the top 25, falling 10 points shy of the last spot.Two of the other three teams - Miami and Texas A&M - spent most of the season in the AP poll. Miami was ranked for each of the final 17 weeks, climbing as high as No. 7. Texas A&M was ranked for all but four weeks, reaching the No. 5 spot in late January.Syracuse is the only surprising squad in the Sweet 16, making it to the second weekend for the first time since 2013. That year was the last in a stretch of four Sweet 16 appearances in five years.Here's a closer look at this year's Sweet 16 field:******LOOK OUT FOR NO. 1... For the first time since 2012, all four No. 1 seeds have advanced to the Sweet 16. Kansas and North Carolina made it look easy, winning each of their games by double digits. Virginia fought off a tough Butler team in the second round, and Oregon got all it could handle from Saint Joseph's after rolling past Holy Cross. In 2012 only one of the No. 1 seeds (Kentucky) made the Final Four while one (Michigan State) lost in the Sweet 16 and two (Syracuse and North Carolina) in the Elite 8.******ACC ROLLING... The Atlantic Coast Conference put seven teams into the NCAA Tournament, matching the Pac-12 and Big 12 for the most. Six ACC teams - North Carolina, Virginia, Miami, Duke, Notre Dame and Syracuse - are still standing, the most to make the Sweet 16 from a single conference in tournament history.******GETTING OFFENSIVE... The old saying is defense wins championships. That may be true, but the common thread among this year's Sweet 16 teams is how efficient they are on offense. Thirteen teams rank in the top 25 of KenPom.com's adjusted offensive efficiency rankings. Wisconsin is the least efficient offensive team by this metric, ranking 88th, but is one of six remaining teams in the top 12 of the adjusted defensive efficiency rankings.******STREAK CONTINUE... If this year's field of 16 looks familiar, it's because six teams returned from last year, Notre Dame, Wisconsin, North Carolina, Oklahoma, Duke and Gonzaga. With its win over Xavier, Wisconsin became the only active team to make three straight Sweet 16s as well as the only program to make five of the past six. Duke, the reigning national champion, has made five of the past seven regional semifinals.