Spinosaurus aegyptiacus ("Egyptian spine lizard") is a theropod dinosaur genus from the Albian to early Cenomanian stages of the Cretaceous time, about 95 to 93 million years ago. Its distinctions comprise being the biggest meat-eating of all dinosaurs, rivaling even Tyrannosaurus rex (at somewhere between 40 and 60 feet (12 to 20 meters) long, 16 to 20 feet (4.8 to 6 meters) tall, and 5 to 7 tons), having large bones extending from the vertebrae up to 6 feet long. These spines most probable had skin or a membrane stretching between them, forming a sail-like arrangement. Spinosaurus provides the name of a family of dinosaurs, the Spinosauridae, of which other members include Angaturama (probably synonymous with Irritator), Baryonyx, Irritator, Suchomimus, and Siamosaurus.

Much mystery environs the nature of this animal. First of all, although it has been well-known to dinosaur enthusiasts because of its strange features, even before it was popularized by its role as main rival in Jurassic Park III, it is mostly known through remains that have been destroyed, aside from a few more newly discovered teeth. Unpublished jaw and skull material suggest that it may have had one of the longest skulls of any carnivorous dinosaur. Initially 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 convey back to the Munich Museum in Germany, and the remaining bones were completely lost due to Allied bombing in 1944.

Aside from its sail, notable individuality of Spinosaurus includes:

Long, narrow snout similar to other Spinosaurids, and like them overflowing with conical teeth.

v Slender build.

One enlarged, hook-like claw on each of its front limbs, perhaps for infectious fish.

Relatively short legs and long arms, leading some paleontologists to propose it may have been quadrupedal, rather than severely bipedal (though it was undoubtedly capable of at least facultative bipedality).

Much of this is conjecture based on Baryonyx and other Spinosaurids, as no limb material has ever been credited to Spinosaurus.

Scientists differ whether Spinosaurus was a cursorial predator (like Tyrannosaurus rex) or a docile fisher, sitting lazily by riverbanks and snatching up powerless prey as they swam by. In Jurassic Park III, it is portrayed as a lethal and unsafe killer, even winning a battle with a Tyrannosaurus. However as noted above, in spite of its length, it was more lightly built than Tyrannosaurus and other theropods, and its stretched out jaws and conical teeth suggest it may have mainly eaten fish, or else fed on carrion, rather than being a hunter of large prey like Tyrannosaurus.

Also, the reason of its sail is unclear. Scientists have optional 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 almost certainly only be based on speculation. The fact that other dinosaurs of the same time and area, namely the ornithopod Ouranosaurus and the sauropod Rebbachisaurus, possessed a alike structure is interesting. The sail is possible analogous (not homologous) to that of the Permian mammal-like reptile, Dimetrodon, who lived previous to the dinosaurs even appeared, strongly points in the direction of parallel evolution.

It is very likely that the sail was very vascular and used by the animal to heat itself up when sunrise took place, by rotating the sail at a 90 degree angle to the rising sun. This would entail that the animal was only partly warm-blooded at best and lived in climates where nighttime temperatures were cool or near to the ground and the sky usually not cloudy. It is consideration that Spinosaurus and Ouranosaurus both lived in or at the margins of an earlier version of the Sahara Desert, which would explain this.