Spinosaurus (meaning “spine lizard”) is a genus of bipedal theropod dinosaur from the middle Cretaceous, about 95 to 93 million years ago. Its distinctions include being one of the largest meat-eating dinosaurs, rivaling even Tyrannosaurus rex (at somewhere between 40 and 50 feet long, 16 to 20 feet tall, and 5 to 7 tons), having large bones extending from the vertebrae up to 6 feet long. These spines most likely had skin or a membrane stretching between them, forming a sail-like structure. Spinosaurus provides the name of a family of dinosaurs, the Spinosauridae, of which other members include Angaturama , Baryonyx, Irritator, Suchomimus, and Siamosaurus .

Much mystery surrounds the nature of this animal. First of all, although it has been well-known to dinosaur enthusiasts because of its unusual features, even before it was popularized by its role as main antagonist in Jurassic Park III, it is mostly known through remains that have been destroyed, aside from a few more recently discovered teeth. Originally found in the Baharija Valley of Egypt in 1912, it was named by German paleontologist Ernst Stromer in 1915. Some of the fossils were damaged during transport back to the Munich Museum in Germany, and the remaining bones were completely lost because of Allied bombing in 1944.

Also, the purpose of its sail is unclear. Scientists have suggested it could have been used to regulate temperature, or to attract mates, or to intimidate rivals. However, the use of such an odd structure can probably only be based on speculation. The fact that other, unrelated animals, such as the herbivorous dinosaur Ouranosaurus and the mammal-like reptile, Dimetrodon, which lived at the end of the Paleozoic Era, before the dinosaurs even appeared, also possess this structure makes its role in relation to evolutionary development perplexing.

Lastly, its diet remains a topic of debate. In Jurassic Park III, it is portrayed as a lethal and dangerous killer, even winning a battle with a Tyrannosaurus. However, despite its large size, it was more lightly built than Tyrannosaurus and other theropods, and its elongated jaws and thin, conical teeth suggest it may have largely eaten fish, or else fed on carrion, rather than being a hunter of large prey.