Okay. Check out the techtree.ttree file (Sunflowers\Paraworld\Data\Boosterpack1\Scripts\Server\settings\techtree), there all units' and buildings' costs, strenght, their upgrades and levelup strenght gains are coded.
Copy all files from one certain unit, e.g. aje_allosaurus (allosaurus rider of the dustriders) and rename the copy to a name of your choice, maybe aje_carnotaurus_rider will fit. Then you have to change everything that redirects to the allosaurus unit to the adequate bonuses for your carnotaurus rider, for example the unit animation is 'aje_allosaurus'. Change this to 'carnotaurus' and the unit you control is a wild carnotaurus. If you leave the line called rider = 'aje_rider_1' or aje_rider_2, I don't know which one it is, the carnotaurus you can build from the animal farm will have an amazon riding it.
Well, that's pretty much it. The only thing that could prove to be a problem is that some wild animals' animations cannot be controlled, maybe the one for carnotaurus can neither..