The Sarcosuchus is an antagonist in The Land Before Time X: The Great Longneck Migration.
The first time it appears disguises itself as a stone and Littlefoot tried to jump on it. It tried to bite him but was trodden on by Sue the Supersaurus. Later it attacks his friends as they pass through. It almost eats Petrie but Cera accidentally makes a log land on it. (it wasn't really red - it's an effect used several times in LBT but never before this drastically, only the sky) Five more appear in The Amazing Threehorn Girl. They come into the Great Valley through a hole in the Great Wall. Two chase the gang. They go after Cera when she goes the other way from the rest but are scared away when she knocks down some rocks by accident. The characters believe they have left the valley and the adults seal the opening - but ominously there is no sign of the crocodilians, the reason being that they have not left the valley.
For rescuing her friends Cera is thought to be a hero and although reluctant at first she begins to exaggerate the story a little bit more each retelling. To prove to Chomper that Cera is lying Littlefoot and Petrie take him to the sight were the Sarcosuchus cornered Cera. However they end up seeing a huge Sarcosuchus and two smaller ones heading towards the middle of the valley. When this is revealed and it turns out Cera was lying the adults try to chase her out of the valley. She runs away and is attacked by all five Belly Draggers. Her father arrives and fights them off, and they are chased from the valley for real since he push this crocodilian down on the ground, bites his tail, and swings it round and round and throws it in the air which makes them scared, threatened and forced to flee immediately. And it land on top of this brown one when its right behind the others.