This model is my counts-as Thunderfire Cannon. It's based on the old metal Lizardmen Stegadon model, with the horns replaced by brain-implants. The turret consists of a regular, round 25mm base (with those weird hooks from the vehicle accessory sprue stuck on the side) topped with a Rhino driver's hatch. The gun itself is a cut-down twin-linked lascannon with the covering plate of the Vindicator's robot-arm (the one that holds the shell) stuck on top.
The Techmarine is made from an old metal Techmarine torso, head and axe (I think it's from the BA Honour Guard Tech-adept), and regular Space Marine bits. You may note he does not come with the flamer and twin-linked plasma pistol, as I had no way of adding them without making him look silly.
Here's some WIP shots to better show you the conversion work:
Unlike the Carnosaurs or raptors these beasts are not psychically controlled, but simply lobotomised and remote-controlled by Techmarines.
In game I really enjoy using this guy. 4 blasts put out an incredible number of hits on infantry squads, and with S6 or S5 ignore cover shots he can threaten light vehicles as well. Even Land Raiders aren't completely safe against it, since they need to pass Dangerous Terrain checks to move after a hit from a Tremor shell.
Of course, the main weakness of the unit is the vulnerability of the cannon itself. The main thing to keep in mind here is the range of the gun: 60". That is a distance it shares with but a handful of other direct-fire heavy weapons (and most artillery). If you have second turn, you can deploy the Cannon out of range of at least a portion of the enemy, while still being in range yourself.
You can also completely hide it for at turn behind a Land Raider or Rhino, then drive away to reveal targets for the Cannon in a later turn. This exposes the Cannon but usually all you need is a single Shooting Phase to justify its presence on the table.
Unfortunately this guy, the Carnosaurs and the Cold One bikers are the only dinosaurs present in the army as of yet. I would love to add Terradons to the mix, but I have no idea what to use them for. I was considering Attack Bikes, with possibly a Jump Pack Marine added as a handler, but in my mind that just looks stupid.