Monday ended just as it began in the NFL head coaching turnstile, with six vacancies, as the Buffalo Bills officially announced the hiring of Rex Ryan while the Denver Broncos and John Fox parted ways a day after the stunning home loss to the Indianapolis Colts.

Ryan was also a candidate with the Atlanta Falcons and San Francisco 49ers, who along with the Chicago Bears, New York Jets and Oakland Raiders have been conducting their due diligence with a host of interviews.

The leading candidates for each opening:

49ers: Defensive coordinators Todd Bowles (Arizona) and Dan Quinn (Seattle) are near the top of several teams’ lists, and Broncos offensive coordinator Adam Gase would make an intriguing fit with quarterback Colin Kaepernick. Fox will also shoot to the top of the list. Mike Shanahan remains in the picture as a potential package deal with son Kyle, who would come in as the offensive coordinator and head coach in waiting. Jim Tomsula and Vic Fango are in-house candidates who are popular among the players.

Bears: Chicago is reportedly interested in Ravens offensive coordinator Gary Kubiak, who indicate he plans to remain with Baltimore. Bowles, Gase, Quinn, Shanahan and Lions defensive coordinator Teryl Austin are under strong consideration.

Broncos: Gase will immediately be pegged as a potential promotion to the head spot, especially if quarterback Peyton Manning indeed returns for one stab at that elusive second title.

Falcons: Changes to the front office structure have slowed the process, and may have scared away Ryan. But the Falcons are interested in many of the same names, including Austin, Bowles, Gase, Quinn and former Bills head coach Doug Marrone. New England offensive coordinator Josh McDaniels is another name to watch.

Jets: Quinn reportedly is the frontrunner, although that could change if the Seahawks reach the Super Bowl, making him unavailable for another two weeks. Former Bills head coach Doug Marrone reportedly bombed his interview with the team last week, but still can’t be ruled out. Other names to watch include Kubiak, Carolina defensive coordinator Sean McDermott and Seattle offensive line coach Tom Cable.

Raiders: The team is expected to speak a second time with Broncos defensive coordinator Jack Del Rio. The dramatic storyline would be a potential second run with Mike Shanahan. Bowles and offensive coordinators Darrell Bevell (Seattle), Pat Shurmer (Philadelphia) and Pep Hamilton (Indianapolis) have also drawn interest, as has Dallas passing game coordinator Scott Linehan.