The Spinosauridae (or spinosaurids) are a clade or family of theropod dinosaurs comprising ten to fourteen known genera. They came into prominence during the Cretaceous period. Spinosaurid fossils have been recovered worldwide, including Africa, Europe, South America and Asia. Their remains have generally been attributed to the Early to Mid Cretaceous.
Spinosaurids were large bipedal carnivores. Their crocodilian-like skulls were long, low and narrow, bearing conical teeth with reduced or absent serrations. The tips of their upper and lower jaws fanned out into a spoon-shaped structure similar to a rosette, behind which there was a notch in the upper jaw that the expanded tip of the lower jaw fit into. The nostrils of spinosaurids were retracted to a position further back on the head than in most other theropods, and they had bony crests on their heads along the midline of their skulls. Their robust shoulders wielded stocky forelimbs, with three-fingered hands that bore an enlarged claw on the first digit. In many species, the upwards-projecting neural spines of the vertebrae (backbones) were significantly elongated and formed a sail on the animal's back (hence the family's etymology), which supported either a layer of skin or a fatty hump.
The genus Spinosaurus, from which the family, subfamily (Spinosaurinae), and tribe (Spinosaurini) borrow their names, is the longest known terrestrial predator from the fossil record, with an estimated length of up to 15 meters (49 ft). The closely related genus Sigilmassasaurus may have reached a similar or greater size, though its taxonomy is disputed. Direct fossil evidence and anatomical adaptations indicate that spinosaurids were at least partly piscivorous (fish-eating), with additional fossil finds indicating they also fed on other dinosaurs and pterosaurs. The osteology of spinosaurid teeth and bones has suggested a semiaquatic lifestyle for some members of this clade. This is further indicated by various anatomical adaptations, such as retracted eyes and nostrils; and the deepening of the tail in some taxa, which has been suggested to have aided in underwater propulsion akin to that of modern crocodilians.
The first spinosaurid fossil, a single conical tooth, was discovered circa 1820 by British paleontologist Gideon Mantell in the Wadhurst Clay Formation.[7] In 1841, naturalist Sir Richard Owen mistakenly assigned it to a crocodilian he named Suchosaurus (meaning "crocodile lizard").[8][9] A second species, S. girardi, was later named in 1897.[10] However, the spinosaurid nature of Suchosaurus was not recognized until a 1998 redescription of Baryonyx.[11]
The first fossils referred to a spinosaurid were discovered in 1912 at the Bahariya Formation in Egypt. Consisting of vertebrae, skull fragments, and teeth, these remains became the holotype specimen of the new genus and species Spinosaurus aegyptiacus in 1915, when they were described by German paleontologist Ernst Stromer. The dinosaur's name meant "Egyptian spine lizard", in reference to the unusually long neural spines not seen previously in any other theropod. In April 1944, the holotype of S. aegyptiacus was destroyed during an allied bombing raid in World War II.[12][13] In 1934, Stromer referred a partial skeleton also from the Bahariya Formation to a new species of Spinosaurus,[14] this specimen has since been alternatively assigned to another African spinosaurid, Sigilmassasaurus.[15]