Sarcosuchus imperator was a huge crocodilian reptile from the Late Cretaceous, of the ancient Mesosuchian Pholidosaurs, that had an upper length of about 12 metres and a weight of 10 tonnes. It is known from North Africa - though it is shown somewhat erroneously in South America in 'Land of Giants', it maybe possible it could have been found here due to the shape of the continents in its time. It is the largest Crocodilian of all time, depending on whose figures you read.
It would have been a sinister ambush predator, easily capable of preying on even some of the larger Sauropod Dinosaurs. It has been speculated that a clash of the titans between Sarcosuchus and the gigantic theropod mega carnivores of North Africa, such as Suchomimus, Carcharodontosaurus and the infamous Spinosaurus, may have been not so uncommon over 100 million years ago. It was an age of giants, and they fought tooth and claw. Nevertheless, it may well be more realistic to imagine that such mighty reptile enemies would usually just try to avoid each other, or that the immense Spinosaurus for example could have been so large that really even a monster like Sarcosuchus would typically back down.
Sarcosuchus doesn't appear in the main series of Walking with Dinosaurs, but its close relative Deinosuchus, which is smaller but no less massive, makes an appearance in Death of a Dynasty and Prehistoric Park. It should be noted that these animals, though superficially similiar, are of very different appearence.
Sarcosuchus appeared in the first episode of Chased By Dinosaurs, "Land of Giants". One of the species lunges at and tries to eat Nigel Marven more than once. Nigel also demonstrates the power of the Sarcosuchus by inserting a thick wooden stick into its mouth, and filming it snapping it in two.
At the end of Land of Giants, the sarcosuchus tries to eat Nigel and the Cameraman. The camera has been eaten, and we don't know if Nigel and his cameraman are alive.
It also appeared in Animal Planet the Most Extreme in Awesome Ancestors where its version was the same clips from Chased By Dinosaurs