In addition, rookie linebacker Kelvin Smith and rookie tackle Julius Wilson were signed off the practice squad.
The moves left the Dolphins with 52 players on the active roster.
The big news obviously was the move involving Thomas, a move that really wasn't all that surprising.
Thomas had missed the last five games because of what the team described as "migraines," this after he missed two games early in the season after sustaining a concussion.
"I'm disappointed with the decision to place me on injured reserve," Thomas said in a team-released statement. "I expected to come back this season and still think I can. However, I respect the team's decision and look forward to playing next year."