Well, the Dontarrious Thomas era ended before it really even got going.  The team released Thomas and signed for Cincinnati Bengals LB Ahmad Brooks.  Here's a brief scouting report on Brooks from ESPN:

His durability is a concern . . . He has excellent size for the middle in either a 4-3 or 3-4 scheme and is aggressive with some natural playmaking ability . . . He has enough speed to make plays outside the tackle box when he takes good angles. Brooks is a powerful, jarring tackler who arrives with some nastiness. His recognition and instincts need to improve . . . Brooks remains a work in progress and he has to stay on the field with more regularity to reach his potential, but there is a lot to build on here and he could have a bright future.

When the 49ers first signed Thomas, his scouting report sounded similar in that he has the physical ability but has to learn the mental side of things.  So I guess they saw enough of Thomas to decide they might as well try somebody a little different?

EDITOR'S UPDATE 2:40PM: Kirkendall over at Cincy Jungle was kind enough to throw some information my way about Ahmad Brooks:

You might like this guy. He's been a guy that's full of potential, based on his beastly size and super-aggression on the field. At the same time, he still has durability issues and has often times over-run plays and forgotten assignments. He's a good pass rusher up the middle though...

I asked him about his abilities on special teams since backing up Patrick Willis would mean not a lot of regular linebacker time.  I was curious if mental issues would hurt him on special teams:

Not really. The very nature of special teams, for the most part, is too simple for a man like Brooks to screw up. The dude can run, hit and pile-drive people through concrete walls. His biggest problem has always been a mental make-up; taking a long time understanding his role and assignments.

Real quick, Brooks has been a middle linebacker for a majority of his career. The Bengals decided to move him to strong-side backer this offseason, before dumping him.

So does that mean maybe the 49ers use him as an outside linebacker as well, or will he strictly back up Bamm Bamm?