Spinosaurus

Spinosaurus (meaning 'spine lizard') is a genus of large spinosaurid theropod dinosaurs. They lived in what is now North Africa during the Cenomanian age of the Late Cretaceous period, about 100 to 94 million years ago. The first remains were found in Egypt in 1912. German palaeontologist Ernst Stromer described them in 1915. The original remains were destroyed in World War II, but more material was found in the early 21st century.

Scientists are not sure whether the fossils show one species or two. The type species, S. aegyptiacus, is mainly known from the Bahariya Formation in Egypt and the Kem Kem beds in Morocco. The other species, S. mirabilis, is known from the Farak Formation in Niger. Some other names may belong to the same animals, such as Sigilmassasaurus and the dubious S. maroccanus from the Kem Kem beds, and Oxalaia from the Alcântara Formation in Brazil. Scientists still debate whether these taxa are really different.

Spinosaurus is one of the largest known land carnivores. Other large meat-eaters of its time include Tyrannosaurus, Giganotosaurus and the Carcharodontosaurus. A 2022 study suggests that S. aegyptiacus could have reached 14 m (46 ft) in length and weighed 7.4 t (8.2 short tons). Its skull was long, low and narrow, a bit like that of a modern crocodilian. It had straight, cone-shaped teeth with few or no serrations. Its strong forelimbs had three-fingered hands, with a large claw on the first digit. Its tall neural spines, which were long extensions of the vertebrae, grew at least 1.65 m (5.4 ft) long. They were probably joined by skin, forming a sail-like structure. Its long, narrow tail was made deeper by tall, thin neural spines and long chevrons, forming a paddle-like shape.

Spinosaurus ate both water animals and land animals. Evidence suggests it was semiaquatic, although scientists strongly disagree about how well it could swim. Its leg bones were very dense, which helped it control buoyancy. Several uses have been suggested for the back sail, including thermoregulation and display, perhaps to scare off rivals or attract mates. It lived in a warm, wet place of tidal flats and mangrove forests. Many other animals lived there too, including other dinosaurs, fish, crocodylomorphs, squamates, turtles, pterosaurs, and plesiosaurs.

Discovery and naming

In October 1898, French geologist Fernand Foureau found two unusual teeth in Cenomanian-aged sediments in what is now southern Algeria. He found them on the Foureau-Lamy Expedition, which crossed the Sahara. In 1905, French geologist Emile Haug thought the teeth came from a fish. In 1915, German paleontologist Ernst Stromer decided they belonged to Spinosaurus.

In 1912, fossil collector Richard Markgraf found the first clearly identifiable remains in the Bahariya Oasis of western Egypt. In 1915, Stromer named them a new genus and species of dinosaur, Spinosaurus aegyptiacus. The name means "spine lizard," and the species name refers to Egypt. A later skeleton from the same oasis was described in 1934. The Spinosaurus fossils kept at a museum in Munich were lost when the building was damaged during World War II.

In the 1980s, more Spinosaurus material was found in Algeria, Morocco, and Tunisia. These pieces were often small and incomplete. In 1996, Canadian paleontologist Dale Russell named a new species from Morocco, S. maroccanus. However, most researchers now think it is either doubtful or the same as S. aegyptiacus.

Starting in 2008, fossils from Morocco were shown to Nizar Ibrahim, an Italian paleontologist. He thought they might belong to Spinosaurus. Ibrahim and others later found a partial skeleton. In 2014, they proposed it as a new reference specimen, called a neotype, for S. aegyptiacus. In 2015, some scientists disagreed. They argued the specimen came from a different location and might not belong to the same animal. Between 2015 and 2019, more fossils from the site were found. In 2020, researchers described the tail. Scientists are still debating how these fossils fit with the earlier finds.

Description

Spinosaurus is often counted among the largest theropod dinosaurs. Friedrich von Huene in 1926 and Donald F. Glut in 1982 both listed it among the biggest theropods, at about 15 m (49 ft) long and over 6 t (6.6 short tons) in weight. Later scientists gave other sizes, from about 12.6 m to 18 m long, so its exact size is still uncertain. In 2005, Dal Sasso and colleagues compared it with the related Suchomimus. Its skull had a narrow snout and straight, cone-shaped teeth with no serrations. The teeth at the very front of the upper jaw were bigger than the others. A small crest sat in front of its eyes.

Like other spinosaurids, it had a long, muscular neck that curved in a sigmoid S-shape. Its front legs were large and sturdy, with three clawed digits on each hand. Its long phalanges and claws suggest its hands were long too. Its most famous feature was its "sail," made of very tall spines on its back bones. These spines were unlike the thin rods of Edaphosaurus, Ianthasaurus and Dimetrodon, or the thicker spines of the iguanodontian Ouranosaurus. Other dinosaurs, such as Ouranosaurus and the Early Cretaceous sauropod Amargasaurus, may have had similar bone features. The sail may be an analog of the sail of the Permian synapsid Dimetrodon. The two evolved separately, through a process called convergent evolution. Some scientists think the structure was more like a hump than a sail. Ibrahim and colleagues suggested the spines were covered by skin, like a crested chameleon. Its pelvis was much smaller than those of other giant theropods. Its feet were built for walking on unstable ground, like shorebirds, and may have been webbed. Its tail was deep and narrow, similar to the tails of newts and crocodilians.

Classification

Spinosaurus is the main, or type, member of the Spinosauridae family of dinosaurs. It belongs to the subfamily Spinosaurinae, which also includes Oxalaia, Irritator, and Angaturama. The German scientist Ernst Stromer named Spinosauridae after Spinosaurus alone. He saw some likenesses to Dryptosaurus and Tyrannosaurus, but he put Spinosaurus in its own group because its teeth, bones, and jaw were very unusual. For many years, scientists thought spinosaurids were a megalosaurid or a carnosaur. Later, researchers found that spinosaurids formed a group spread across several continents. In 1986, scientists described Baryonyx as its own family. In 1988, Gregory S. Paul suggested it was related to Spinosaurus. Since the 1990s, spinosaurids have been found in Africa, Asia, Europe, and South America.

Scientists have studied how spinosaurids are related in many ways. In 1998, Sereno and his team described Suchomimus and split Spinosauridae into two subfamilies: Baryonychinae and Spinosaurinae. In 2004, Thomas Holtz and his colleagues defined Spinosaurinae more clearly. Spinosaurines have straight teeth without serrations, spaced far apart. Baryonychines have many curved teeth with serrations. A 2017 study by Marcos Sales and colleagues suggested that some South American spinosaurids fell between the two groups. Sereno's team also found that Spinosaurus mirabilis is closely related to S. aegyptiacus, which supports placing it in the same genus.

Paleobiology

Scientists are not sure what the sail or hump on the back of Spinosaurus was used for. They have suggested several hypotheses, including heat control and display. The sail may have helped the animal warm up or cool down through thermoregulation. Large animals find it hard to get rid of extra heat, an idea linked to Haldane's principle. The sail may also have helped attract mates, much like a peacock's tail. Later researchers suggested that the sail worked like the fins of sailfish, helping the animal move through water in a hydrodynamic way. They also suggested that its long tail could stun fish, like a thresher shark. Sailfish herd fish into a "bait ball" to catch them more easily.

Spinosaurus probably ate many kinds of food. It is unclear whether it was mainly a land hunter or a piscivore, which is a fish eater. Its relative Baryonyx had fish scales in its stomach. A fossil from South America suggests that spinosaurs sometimes ate pterosaurs. Spinosaurus was likely a flexible hunter. It also scavenged and ate small or medium prey. Scientists disagree about how much time it spent in water. A 2010 isotope analysis of its teeth suggested a semiaquatic life. A 2018 study argued that it could not sink and likely spent much of its time on land or in shallow water. Later tail studies suggested it swam well. Some researchers have argued it hunted like herons. A 2026 study found salt glands similar to those of birds that live in brackish and saltwater places.

Scientists have also debated how Spinosaurus moved on land. It is usually shown as a biped, an animal that walks on two legs. It was once shown as a quadruped, an animal that walks on four legs, similar to Dimetrodon. A 2014 study by Ibrahim and colleagues argued for a four-legged animal. Later work found its center of mass was near the hips, which would let it stand upright. Some experts, including Mark Witton, agreed with the proportions in the 2014 study. Others were skeptical of the new reconstruction.

Paleoecology

The holotype specimen of Spinosaurus comes from the Bahariya Formation, a rock layer in North Africa that holds many dinosaur fossils. Fossils have also been found at several other sites, including the Kem Kem Beds of Morocco, the Farak and Echkar Formations of Niger, the Gara Samani Formation of Algeria, and the Chenini Sandstones. At that time, North Africa bordered the Tethys Sea. This made a coastal area covered in mangrove plants, with wide tidal flats and waterways. North Africa has fewer herbivorous dinosaur species compared with meat-eating ones than most fossil sites do. This pattern is known as "Stromer's Riddle." Scientists think the meat-eaters shared their food. Spinosaurids ate fish, and other groups hunted plant-eating dinosaurs. This idea is called niche partitioning. Isotopic evidence supports this idea. The abelisauroid relatives of Deltadromeus and Bahariasaurus may have been omnivorous or herbivorous, filling a role usually held by ornithischians.

Fossil leaves and roots from the Bahariya Formation show a mangrove world with seed ferns and Weichselia reticulata. Alongside the meat-eating dinosaurs Tameryraptor and Bahariasaurus, Spinosaurus is one of several meat-eaters from this formation. Sauropods include the titanosaurs Paralititan and Aegyptosaurus. Abelisaurid dinosaurs also lived there. The formation has also yielded a wing bone that may belong to Anhanguera. Many water animals lived there too, including the pleurodian turtle Apertotemporalis, bony fish Mawsonia and Paranogmius, sawskates Onchopristis and Schizorhiza, sharks Squalicorax and Cretolamna, many invertebrates, and several crocodylomorphs such as the stomatosuchid Stomatosuchus and the eunotosuchian Libycosuchus. The Kem Kem Beds are made of three formations, and Spinosaurus fossils come from two of them. Clues suggest the area had a monsoon season rather than constant rain. This is similar to today's sub-tropical and tropical areas of Southeast Asia and Sub-Saharan Africa. Its river system was freshwater, as shown by lungfishes and other freshwater animals. Giant fish such as the coelacanth Axelrodichthys and the bichir Bawitius lived there. So did crocodile relatives like the aegyptosuchid Aegisuchus, Laganosuchus, the peirosaurid Hamadasuchus, and the pholidosaurid Elosuchus. Many pterosaurs flew over the area. These included the toothed anhanguerids Siroccopteryx and Nicorhynchus, and the toothless edentulous azhdarchoids Alanqa and Leptostomia. Other sauropods include the rebbachisaurid Rebbachisaurus, a somphospondylian titanosauriform, and an unnamed titanosaur. Ornithischian fossils are very rare, while meat-eating dinosaurs are more common. These include Spinosaurus and Sauroniops, which may be a nomem dubium.

Spinosaurus appeared in the 2001 film Jurassic Park III, where it replaced Tyrannosaurus as the main villain. The film's consulting paleontologist, John R. Horner, said that Spinosaurus was the true predator. In the film, Spinosaurus was bigger and more powerful than Tyrannosaurus, and it won a fight between the two. In Jurassic World, a T. rex breaks through a Spinosaurus skeleton in the final fight. The dinosaur also appeared in many Jurassic Park games, most notably Jurassic World Evolution and its sequels. It returned in the fourth and fifth seasons of Jurassic World Camp Cretaceous, where it faced two T. rex this time. In Jurassic World Rebirth, it appeared in a more realistic form, living alongside a Mosasaurus.

Spinosaurus has long been shown in popular dinosaur books. Only recently has there been enough information about its relatives to show it accurately. After an influential 1955 skeleton reconstruction, based on an earlier diagram, it was treated as a general upright meat-eating dinosaur. It was shown with a skull like other large meat-eaters, a sail on its back, and even four-fingered hands. Besides films, toys, games, and books, Spinosaurus has appeared on postage stamps from countries such as Angola, The Gambia, and Tanzania.