Dawson was last with the Indianapolis Colts. He was a seventh-round draft pick in 2007 and appeared in all but six regular season games over the last four years. He started 14 games in 2008 and recorded 42 tackles. He only made six starts in his other three seasons in Indianapolis.
Stanley was last with the Miami Dolphins. He entered the league as a sixth-round pick of the Dallas Cowboys in 2006 and went on to play for the St. Louis Rams, Atlanta Falcons, New Orleans Saints, Jacksonville Jaguars, Dolphins and the UFL's Omaha Nighthawks. He appeared in 15 games with the Jaguars in 2009 and made 20 tackles and three pass defenses.
To make room on the roster for Dawson and Stanley, the Lions released linebacker Daunte Akra and cornerback Jamal Robinson, who were both originally signed this year as undrafted free agents.
UPDATE: The Lions also released Greg Banks on Monday.
UPDATE II: Adam Caplan reports that the Lions claimed linebacker Cody Brown off waivers from the Jets. This explains why three players were let go on Monday.