Sheridan, who is taking over for Matt Burke as the Lions' linebackers coach, is from Detroit. He went to Grand Valley State, and he actually coached linebackers at Michigan State from 1998-2000. He later served as an assistant at Michigan from 2002-04, and he was most recently the Tampa Bay Buccaneers' defensive coordinator from 2012-13.
Austin, who was the favorite all along to replace Gunther Cunningham and be Jim Caldwell's defensive coordinator, also was once an assistant at Michigan (from 1999-2002). In the NFL, he's been a defensive backs coach for the Seattle Seahawks, Arizona Cardinals and Baltimore Ravens, and he went to the Super Bowl with all three teams. He was most recently with the Ravens from 2011-13, and he went to Baltimore after spending a year as the defensive coordinator at Florida.
In addition to announcing these two hires, the Lions also officially retained several assistant coaches on Friday.