Spinosaurus (meaning "spine lizard") is a genus of spinosaurid dinosaur that lived in what now is North Africa during the Cenomanian to upper Turonian stages of the Late Cretaceous period, about 99 to 93.5 million years ago.
The genus was known first from Egyptian remains discovered in 1912 and described by German palaeontologist Ernst Stromer in 1915.
The original remains were destroyed in World War II, but additional material came to light in the early 21st century.
It is unclear whether one or two species are represented in the fossils reported in the scientific literature.
The best known species is S. aegyptiacus from Egypt, although a potential second species, S. maroccanus, has been recovered from Morocco.
The contemporary spinosaurid genus Sigilmassasaurus has also been synonymized by some authors with S. aegyptiacus, though other researchers propose it to be a distinct taxon.
Another possible junior synonym is Oxalaia from the Alcântara Formation in Brazil.
Spinosaurus is the longest known terrestrial carnivore; other large carnivores comparable to Spinosaurus include theropods such as Tyrannosaurus, Giganotosaurus and Carcharodontosaurus.
The most recent study suggests that previous body size estimates are overestimated, and that S. aegyptiacus reached 14 metres (46 ft) in length and 7.4 metric tons (8.2 short tons) in body mass.
The skull of Spinosaurus was long, low, and narrow, similar to that of a modern crocodilian, and bore straight conical teeth with no serrations.
It would have had large, robust forelimbs bearing three-fingered hands, with an enlarged claw on the first digit.
The distinctive neural spines of Spinosaurus, which were long extensions of the vertebrae (or backbones), grew to at least 1.65 meters (5.4 ft) long and were likely to have had skin connecting them, forming a sail-like structure, although some authors have suggested that the spines were covered in fat and formed a hump.
The hip bones of Spinosaurus were reduced, and the legs were very short in proportion to the body.
Its long and narrow tail was deepened by tall, thin neural spines and elongated chevrons, forming a flexible fin or paddle-like structure.
Spinosaurus is known to have eaten fish, and most scientists believe that it hunted both terrestrial and aquatic prey.
Evidence suggests that it was highly semiaquatic, and lived both on land and in water much like modern crocodilians do.
Spinosaurus's leg bones had osteosclerosis (high bone density), allowing for better buoyancy control, and the paddle-like tail was likely used for underwater propulsion.
Multiple functions have been put forward for the dorsal sail, including thermoregulation and display; either to intimidate rivals or attract mates.
It lived in a humid environment of tidal flats and mangrove forests alongside many other dinosaurs, as well as fish, crocodylomorphs, lizards, turtles, pterosaurs, and plesiosaurs.