Although Spinosaurus is well-known to dinosaur enthusiasts due to its size, sail, and elongated skull, it is mostly known from remains that have been destroyed, aside from a few more recently discovered teeth and skull elements. Additionally, so far only the skull and backbone have been described in detail, and limb bones have not been found. Jaw and skull material published in 2005 show that it had one of the longest skulls of any carnivorous dinosaur, estimated at about 1.75 meters long (5.75 ft). The skull had a narrow snout filled with straight conical teeth that lacked serrations. There were six or seven teeth on each side of the very front of the upper jaw, in the premaxilla bones, and another twelve in both maxillae behind them. The second and third teeth on each side were noticeably larger than the rest of the teeth in the premaxilla, creating a space between them and the large teeth in the anterior maxilla; large teeth in the lower jaw faced this space. The very tip of the snout holding those few large anterior teeth was expanded, and a small crest was present in front of the eyes.

The sail of Spinosaurus was formed of very tall neural spines growing on the back vertebrae. These spines were seven to eleven times the height of the vertebrae from which they grew. The spines were slightly longer front to back at the base than higher up, and were unlike the thin rods seen in the pelycosaur finbacks Edaphosaurus and Dimetrodon.

 

 

Spinosaurus gives its name to a family of dinosaurs, the Spinosauridae, of which other members include Baryonyx from southern England, Irritator and Angaturama (which is probably synonymous with Irritator) from Brazil, Suchomimus from Niger in central Africa, and possibly Siamosaurus, which is known from fragmentary remains in Thailand. Spinosaurus is closest to Irritator, which shares its unserrated straight teeth, and the two are included in the subfamily Spinosaurinae. In 2003, Oliver Rauhut suggested that Stromer's Spinosaurus holotype was a chimera, composed of back vertebrae from a carcharodontosaurid similar to Acrocanthosaurus and a dentary from a large theropod similar to Baryonyx. This analysis, however, has been rejected in recent papers.

 

The first described remains of Spinosaurus were found in the Bahariya Valley of Egypt in 1912, and were named by German paleontologist Ernst Stromer in 1915. Fragmentary additional remains from Bahariya, including vertebrae and hindlimb bones, were designated by Stromer as "Spinosaurus B" in 1934.

 

Stromer considered them different enough to belong to another species, and this has been borne out; with the advantage of more expeditions and material, it appears that they either pertain to Carcharodontosaurus or to Sigilmassasaurus. Some of the Spinosaurus fossils were damaged during transport back to the Deutsches Museum, in Munich, Germany, and the remaining bones were completely lost due to Allied bombing in 1944.

 

Two species of Spinosaurus have been named: Spinosaurus aegyptiacus (meaning "Egyptian spine lizard") and Spinosaurus marocannus (meaning "Moroccan spine lizard"). S. marocannus was originally described by Dale Russell as a new species based on the length of its neck vertebrae. Later authors have been split on this topic, some considering the length of the vertebrae to be variable from individual to individual and therefore regarding S. marocannus as invalid or a synonym of S. aegyptiacus, and others retaining it as valid.

 

Information sourced from Wikipedia