Like the rest of the prehistoric animals that featured in Turok franchise, the Terror Birds are survivors of the extinction era on Earth due to a number of their population stumbled upon one of the gateways to the Lost Land, artificially created planet which has many portals that connected to Earth which each of them opened in different timelines, and one of them opens during the era where their kinds still lived. The Terror Birds would later entered the said gateway and arrived to the Lost Land. They managed to adapted there as their new home, which in doing so unfortunately, left the rest of their kind on Earth dies when the exinction era began.
Events in Turok: Son of Stone
While Chichak was taking Catori hostage and warning Turok and Andar to back off or she'll be killed as they unknowingly entered one of the hidden gateway to the Lost Land, a wild Terror Bird shows up and attacks. Galloper shrieks in terror as the Terror Bird attacks, slicing her neck. As Galloper is then shown headless as the body falls on the ground. Then, the Terror Bird drops Galloper's head with her eyes still opened instead of closed.
The Terror Bird successfully shrieks with victory, but only to see Turok and Andar preparing to fight it. Turok jumps on it, but only to get knocked down by the Terror Bird. Andar then shoots an arrow at it. As Catori struggles to get free, Chichak knocks her out and quickly gets away with the two rapidly distracted by the Terror Bird. Turok stabs the Terror Bird with his tomahawk, but the Terror Bird pushes him. Andar then shot its eye with a second arrow. The Terror Bird then squabbles away with pain. It is unclear what happened to it, but it is possible that it barely died from the wounds it received that causes it suffers blood loss.
Later, Turok, Andar, and Catori encounter a group of Native Americans who use tamed Terror Birds as mounts.