49’ers officially signed running back DeShaun Foster on Monday. Foster spent all six of his NFL seasons with the Carolina Panthers, rushing for 3,336 yards and 10 touchdowns while catching 126 passes for 996 yards and four more scores. Meantime, the Niners also signed linebacker Dontarrious Thomas and quarterback J.T. O’Sullivan. Thomas amassed 145 tackles and one-and-a-half sacks in four seasons with the Minnesota Vikings. O’Sullivan threw for 148 yards in four games with the Detroit Lions last year.