Brachiosaurus is currently the only NPC in Primal Carnage. A few of them appear in Ruthless and Forgotten Outpost as non-interactable NPCs.They were supposed to appear in Primal Carnage genesis, as seen in the cinematic trailer.
Brachiosaurs also make cameo appearances in Primal Carnage: Extinction. They use their model from PC: genesis and can be seen roaming in the backgrounds of the Ruthless and Docks maps.
If you go into spectator mode on a certain map, you may be able to find their raw models.