Therizinosaurus has large and strong jaws which it can use to pick Regina and throw her against walls or the floor. They often hunt in pairs and are extremely tough. Therizinosaurus is something of an upgraded raptor, and will often be found in large corridors where raptors were more commonly found.One of the more deadly attacks is the Therizinosaurus biting down on Regina's shoulder and shaking her back and forth, which can cause massive damage (as one might believe) and an instant-kill "Death stomp" . It should be noted that Therizinosaurus can sometimes follow Regina into other rooms if she runs away from them with them chasing her. Most notably, The cooridor on floor B3 that leads into the room with the passage way to the docks. Therizinosaurs will follow her into this area if she runs away and they give chase.
If the player meets one, escaping is recommended because they have high resistance to many different weapons. However, if faced with an unavoidable fight, the player's best weapon choice is any kind of grenade round. However, in the second cooridor, the security laser shutters (in the area shown in the previous screenshot.) can be used to trap them by tricking them into following Regina and running around the Therizinosaurs when they reach the other side and closing it behind them. This will get them stuck and they will be unable to attack Regina on the other side. They should remain there for the rest of the game or until Regina opens the shutters again.
Therizinosaurs were in reality quite harmless herbivores of much greater proportions. Therizinosaurs grew to be up to 40 feet long and had potbellies. They did have long claws (that were about the length of the average human arm) like the creature in the game but didn't use them to hunt prey, merely to grasp vegetation and defend against predators.
However the monster seen in the game was made much smaller (to fit inside the narrow corridors of the facility) and much more dangerous. However, Therizinosaurus is relatively new to paleontology (discovered by Evgeny Maleev in 1948) and back during development of the first game, much less was known about the strange dinosaur.
Therizinosaurs are large herbivores that are believed to have lived in Cretaceous period in Mongolia and China.