Spinosaurus aegypticus is a real theropod dinosaur. It was named in the 1940's (or so) based on fragments of the skull and several vertebrae. That specimen was destroyed during a British air raid during WWII. Additional material has been scant, mostly teeth, but most recently, a snout. If you scale up Spinosaurus based on the proportions of its close, better-known relatives (Suchomimus and Baryonyx), then you get an enormous, 56-foot-long animal.
Spinosaurs, as a family, seem adapted for fish-eating. Stress tests done on the skull of Baryonyx show that its skull is constructed like a modern gharial, and oxygen isotope analysis of spinosaur bones are consistent with a semi-aquatic lifestyle. Spinosaurus is the only spinosaurid with a giant sail along its back--its function is unknown, but it could've been a solar radiator, an intimidation device, or a "shade" for fish-catching. Hard to say.
As for the relationship between crocodiles and dinosaurs, both groups lie at opposite ends of a Y-shape called "Archosauria." At the end of the left branch, you've got modern crocodilians. At the end of the right branch, you've got birds. Dinosaurs are on the bird branch, and a bunch of wierd Mesozoic animals, like aetosaurs and poposaurs, are on the crocodile branch.