Defeating Mama Scarface:
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An easy way to kill the giant Tyrannosaur is to quickly run to the giant tree
in the middle of the nest site. Make sure you have a shotgun, explosive tip
arrows, and grenades. Once in the tree, shoot a flare so that the dinosaur's
head is in your line of fire. While she is looking at the flare, shoot every
explosive tip arrow you can at or around the eye area. When she jams her head
in the trunk to eat you, shoot her with the shotgun until she retreats. Once
she frees her head, throw grenades. Repeat this until she falls. Then, quickly
run over to her and finish her off with a knife through the eye.
If done correctly, you should not have died.

in http://www.cheatbook.de/files/turok.htm