The crab is a very common crustacen in the modern seas and coasts and it was also very common in the age of the dinosaurs. In Dinosaur Revolution, crabs are shown in the third episode (Survival Tactics).
The crabs are very common on the Anhanguera scene. They are often hunted by those pterosaurs. It is also shown a young Anhanguera chasing a crab in the coast, but retreats when a metasuchian crocodyliform grabs the crab, drop it and chase the pterosaur.
If a crab loses it's "hand" it grows again but with a different size and form.