Youboty will give the team another cornerback after the Jaguars placed Rashean Mathis on injured reserve with a torn ACL.
Selvie will give Jacksonville more depth at defensive end with Aaron Kampman battling injury issues. Kampman has had two ACL injuries in the past two years, and he pulled a hamstring during the bye week.
Youboty is in his sixth NFL season, and he played in 44 games with seven starts for the Bills the last five years after being drafted on the third round in 2006.
He spent the preseason this year with Tampa Bay but was released in August.
A native of Liberia, Youboty played for two years at Ohio State under current Jaguars defensive coordinator Mel Tucker.
Selvie was a seventh-round draft pick of the Rams in 2010, and he played in all 16 games for St. Louis last year. He was waived at the end of camp this year and was claimed by the Carolina Panthers, for whom he played in four games. He played his college ball at South Florida.