Spinosaurus

***Spinosaurus*** (meaning "spined 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. This 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 has come 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 largest of all known terrestrial carnivores; other large carnivores comparable to *Spinosaurus* include theropods such as *Tyrannosaurus*, *Giganotosaurus* and *Carcharodontosaurus*. Estimates published in 2005, 2007, and 2008 suggested that it was between 12.6 to 18 meters (41 to 59 ft) in length and 7 to 20.9 metric tons (7.7 to 23.0 short tons) in weight. New estimates published in 2014 and 2018, based on a more complete specimen, supported the earlier research, finding that *Spinosaurus* could reach lengths of 15 to 16 meters (49 to 52 ft). The latest estimates suggest a weight of 6.4 to 7.5 metric tons (7.1 to 8.3 short tons). 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[*who?*] have suggested that the spines were covered in fat and formed a hump. *Spinosaurus*'s hip bones 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. *Spinosaurus* 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.

## Description

### Size

Since its discovery, *Spinosaurus* has been a contender for the longest and largest theropod dinosaur. Both Friedrich von Huene in 1926 and Donald F. Glut in 1982 listed it as among the most massive theropods in their surveys, at 15 meters (49 ft) in length and upwards of 6 metric tons (6.6 short tons) in weight. In 1988, Gregory Paul also listed it as the longest theropod at 15 meters (49 ft), but gave a lower mass estimate of 4 metric tons (4.4 short tons).

In 2005, Dal Sasso and colleagues assumed that *Spinosaurus* and the spinosaurid *Suchomimus* had the same body proportions in relation to their skull lengths, and thereby calculated that *Spinosaurus* was 16 to 18 meters (52 to 59 ft) in length and 7 to 9 metric tons (7.7 to 9.9 short tons) in weight. These estimates were criticized because the skull length estimate was uncertain, and (assuming that body mass increases as the cube of body length) scaling *Suchomimus* which was 11 meters (36 ft) long and 3.8 metric tons (4.2 short tons) in mass to the range of estimated lengths of *Spinosaurus* would produce an estimated body mass of 11.7 to 16.7 metric tons (12.9 to 18.4 short tons).

François Therrien and Donald Henderson, in a 2007 paper using scaling based on skull length, challenged previous estimates of the size of *Spinosaurus*, finding the length too great and the weight too small. Based on estimated skull lengths of 1.5 to 1.75 meters (4.9 to 5.7 ft), their estimates include a body length of 12.6 to 14.3 meters (41 to 47 ft) and a body mass of 12 to 20.9 metric tons (13.2 to 23.0 short tons). The lower estimates for *Spinosaurus* would imply that the animal was shorter and lighter than *Carcharodontosaurus* and *Giganotosaurus*. The Therrien and Henderson study has been criticized for the choice of theropods used for comparison (e.g., most of the theropods used to set the initial equations were tyrannosaurids and carnosaurs, which have a different build than spinosaurids), and for the assumption that the *Spinosaurus* skull could be as little as 1.5 meters (4.9 ft) in length.

### Skull

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 premaxillae, 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 front of the maxilla; large teeth in the lower jaw faced this space. The very tip of the snout holding those few large front teeth was expanded, and a small crest was present in front of the eyes. Using the dimensions of three specimens known as MSNM V4047, UCPC-2, and BSP 1912 VIII 19, and assuming that the postorbital part of the skull of MSNM V4047 had a shape similar to the postorbital part of the skull of *Irritator*, Dal Sasso and colleagues (2005) estimated that the skull of *Spinosaurus* was 1.75 meters (5.7 ft) long, but more recent estimates suggest a length of 1.6–1.68 meters (5.2–5.5 ft). The Dal Sasso and colleagues skull length estimate is questioned because skull shapes can vary across spinosaurid species and because MSNM V4047 may not belong to *Spinosaurus* itself.

### Postcranial Skeleton

As a spinosaurid, *Spinosaurus* would have had a long, muscular neck, curved in a sigmoid, or S-shape. Its shoulders were prominent, and the forelimbs large and stocky, bearing three clawed digits on each hand. The first finger (or "thumb") would have been the largest. *Spinosaurus* had long phalanges (finger bones), and only somewhat recurved claws, suggesting that its hands were longer compared to those of other spinosaurids.

Very tall neural spines growing on the back vertebrae of *Spinosaurus* formed the basis of what is usually called the animal's "sail". The lengths of the neural spines reached over 10 times the diameters of the centra (vertebral bodies) from which they extended. The neural 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*, contrasting also with the thicker spines in the iguanodontian *Ouranosaurus*.

*Spinosaurus* sails were unusual, although other dinosaurs, namely *Ouranosaurus*, which lived a few million years earlier in the same general region as *Spinosaurus*, and the South American sauropod *Amargasaurus,* might have developed similar structural adaptations of their vertebrae. The sail may be an analog of the sail of the Permian synapsid *Dimetrodon*, which lived before the dinosaurs even appeared, produced by convergent evolution.

The structure may also have been more hump-like than sail-like, as noted by Stromer in 1915 ("one might rather think of the existence of a large hump of fat [German: *Fettbuckel*], to which the [neural spines] gave internal support") and by Jack Bowman Bailey in 1997. In support of his "buffalo-back" hypothesis, Bailey argued that in *Spinosaurus*, *Ouranosaurus*, and other dinosaurs with long neural spines, the spines were relatively shorter and thicker than the spines of pelycosaurs (which were known to have sails); instead, the dinosaurs' neural spines were similar to the neural spines of extinct hump-backed mammals such as *Megacerops* and *Bison latifrons*. In 2014, Ibrahim and colleagues instead posited that the spines were covered tightly by skin, similar to a crested chameleon, given their compactness, sharp edges, and likely poor blood flow.

*Spinosaurus* had a significantly smaller pelvis (hip bone) than that of other giant theropods, with the surface area of the illium (main body of the pelvis) half that of most members of the clade. The hind limbs were short, at just over 25 percent of the total body length, with the tibia (calf bone) being longer than the femur (thigh bone). Unlike in other theropods, the hallux (or fourth toe) of *Spinosaurus* touched the ground, and the phalanges of the toe bones were unusually long and well-built. At their ends were shallow claws that had flat bottoms. This type of foot morphology is also seen in shorebirds, indicating that *Spinosaurus*'s feet evolved for walking across unstable substrate and that they may have been webbed.

From the caudal vertebrae of the tail projected significantly elongated, thin neural spines, akin to the condition observed in some other spinosaurids, though to a more extreme degree. Coupled with the also elongated chevron bones on the underside of the caudals, this resulted in a deep and narrow tail with a paddle or fin-like shape, comparable to the tails of newts and crocodilians.

## *Spinosaurus* in The Amazing Dinosaur Adventure

*Spinosaurus* from *The Great Day of the Pterosaurs**Spinosaurus* from *The Hermit of Black Rock*