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Spinosaurus Temporal range: mid Cretaceous
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Sauropsida
Superorder:	Dinosauria
Order:	Saurischia
Suborder:	Theropoda
Superfamily:	Megalosauroidea
Family:	Spinosauridae
Subfamily:	Spinosaurinae
Genus:	Spinosaurus Stromer, 1915
Species
S. aegyptiacus (type) ?S. marocannus Russell, 1996

Spinosaurus (meaning "spine lizard") was a genus of theropod dinosaur that lived in what is now North Africa, from the Albian to early Cenomanian stages of the Cretaceous Period, about 95 to 93 million years ago. It is unclear whether there are one or two species. The best known is S. aegyptiacus from Egypt, though a second species (S. marocannus) has been recovered from Morocco.

The distinctive "spines" of Spinosaurus (long extensions of the vertebrae) grew up to 2 metres (6.6 feet) long and were likely to have had skin connecting them, forming a sail-like structure, although some authors have suggested that they were covered in muscle and formed a hump or ridge. Multiple functions have been put forward for this structure, including thermoregulation and display. According to a study by paleontologist Cristiano Dal Sasso of the Civic Natural History Museum in Milan and his colleagues in 2006, it is the largest of all carnivorous dinosaurs, even larger than Tyrannosaurus rex and Giganotosaurus. If the estimates are correct, Spinosaurus would be the longest theropod, measuring 16 - 18 m long (52.5 - 59.1 ft), around 6 m tall (20 ft), and reached weights up to 9 tons.

Description

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 2006 show that it had one of the longest skulls of any carnivorous dinosaur, estimated at about 1.75 m (5.7 ft). The skull had a narrow snout filled with conical teeth that lacked serrations, not unlike what is seen in other spinosaurids. Its teeth are about two to four inches long. A small crest was also present in front of the eyes.

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

Classification

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

Discovery and species

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; they either pertain to Carcharodontosaurus or to Sigilmassasaurus. Some of the Spinosaurus fossils were damaged during transport back to the Deutsches Museum, 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 Russell as a new species based on the length of its neck vertebrae. However, several later authors considered the length of the neck vertebrae to be variable from individual to individual and therefore consider S. marocannus to be a synonym of S. aegyptiacus .

Six partial specimens of Spinosaurus have been described, the first having been destroyed during World War II. However, detailed drawings and descriptions of the specimen remain. The probable size of these individual spinosaurs can be estimated using comparison to known material from other spinosaurid dinosaurs. (The estimates below are based on and .) In 2002, some dentary material from Tunisia which is very similar to existing material of S. aegyptiacus was described.

IPHG 1912 VIII 19, described by Stromer in 1915, and based on a subadult specimen, was destroyed during Allied bombing in WWII. It is estimated to be around 14 meters in length and to have weighed about 6.7 tons. The material consists of a maxillary fragment (750 mm), an incomplete dentary (the skull is estimated to be 1.45 meters long with a mandible approximately 1.34 meters long), nineteen teeth (62, 126 mm), two incomplete cervical vertebrae, seven dorsal vertebrae (190-210 mm), dorsal ribs, gastralia, and eight caudal centra. This is the specimen that Rauhut thought was chimeric.

CMN 50791, described by Russell in 1996, is the holotype of Spinosaurus marocannus. The material it is based on includes a mid cervical vertebra which is 195 millimeters long, an anterior dorsal neural arch, an anterior dentary, and a mid dentary.

MNHN SAM 124, described by Taquet and Russell in 1998, is estimated to be about 14 meters long and to have weighed about 6.7 tons. The material consists of partial premaxillae, partial maxillae, vomers, and a dentary fragment. (The skull is estimated at approximately 1.42 meters long)

Office National des Mines nBM231, described by Buffetaut and Ouaja in 2002, consists of an anterior dentary.

MSNM V4047, described by Dal Sasso et al. in 2006, is estimated to have been around 16-18 meters in length and weighed around 7 to 9 tons. The massive skull is estimated at 1.75 meters long. The fossils consist of premaxillae, partial maxillae, and partial nasals, which together measure 988 mm long.

UCPC-2, also described by Dal Sasso et al. in 2006, which consists of a 'fluted crest'.

Paleobiology

Spinosaurus has some unusual features which have been the subject of debate thus far:

Size

Since its discovery, Spinosaurus has held the record for longest, and possibly largest, theropod dinosaur (though this fact did not reach the public consciousness until its depiction in the film Jurassic Park III and the description of a new specimen in 2006). Both Huene and Glut listed it as among the most massive theropods or the most massive in their surveys, at upwards of 6 tons in weight and 15 meters (50 feet) in length. In 1988, Paul also listed it as the longest theropod at 15 meters (50 feet), but gave a lower mass estimate. The most recent estimates, based on new specimens list Spinosaurus at 16 - 18 metres (53.3 to 60 feet) long and 7.5 - 9 tons in weight. At least one unpublished survey, suggested that Spinosaurus reached sizes of 12 - 19 tons in weight. These high-end weight estimates were based on the author's estimated 17.4 meter length which was based on comparing the holotype's largest known vertebra (210 mm) with the largest known Baryonyx vertebra. This implied an extremely large overall mass, with an unknown upper bound as apparently the holotype specimens are from animals that weren't fully grown. However, the author of these estimates has recently reduced them to similar sizes suggested by dal Sasso et al.

Sail

Spinosaurus sails were unusual, although other dinosaurs of the same time and area, namely the ornithopod Ouranosaurus and the sauropod Rebbachisaurus, might have developed a similar structural adaptation of their dorsal vertebrae (however, this is not uncontroversial; see the articles about these animals for more information). The sail is possibly analogous (not homologous) to that of the Permian mammal-like reptile, Dimetrodon, which lived before the dinosaurs even appeared (these similarities are presumably due to parallel evolution). The sail may also have been more hump-like than sail-like; as noted by Jack Bowman Bailey most recently, spinosaur spines are not thin rods but broad front to back, rather like those of some types of buffalo, and so may have supported a thicker, fatty structure as opposed to a skin sail.

The function of these sails is uncertain; scientists have proposed several hypotheses:

Heat regulator

If the sail contained abundant blood vessels, the animal could have used the sail's large surface area to absorb heat. This would imply that the animal was only partly warm-blooded at best and lived in climates where nighttime temperatures were cool or low and the sky usually not cloudy. It is thought that Spinosaurus and Ouranosaurus both lived in or at the margins of an earlier version of the Sahara Desert, which could explain this. It is also possible that the sail was used to radiate excess heat from the body, rather than to collect it. Large animals, due to the relatively small ratio of surface area of their body compared to the overall volume (Haldane's principle), face far greater problems of dissipating excess heat at higher temperatures than gaining it at lower. Sails of these dinosaurs added considerably to the skin area of the body, with minimum increase of volume. Furthermore, if the sail was turned away from the sun, or positioned at a 90 degree angle towards a cooling wind, the animal would quite effectively cool itself in the warm climate of Cretaceous Africa.

Sexual display

Elaborate body structures of many modern-day animals usually serve to attract members of opposite sex during mating. It is quite possible that the sails of these dinosaurs were used for courtship, in a way similar to a peacock's tail. Stromer speculated that males and females may have differed in the size of the neural spine. If this was the case, the sails may have been brightly colored, but this is purely speculative.

Intimidating device

The sail was possibly used to intimidate rivals or frighten enemies, making the animal appear to be bigger than it was. The dinosaur could display its sail as a final warning signal, before it would resort to open attack, like modern-day rattlesnakes use their tail.

Finally, it is quite possible that the sail combined all these functions, acting normally as a heat regulator, becoming a courting aid during the mating season, being used to cool itself and, on occasions, turning into an intimidating device when an animal was feeling threatened. Conjecture may even allow that the sail may have changed colour, during any of these functions.

Feeding ecology

It is unclear whether Spinosaurus was primarily a terrestrial predator or a fisher, as indicated by its elongated jaws, conical teeth and raised nostrils. The only direct evidence for spinosaur diet comes from related European and South American species. Baryonyx was found with both fish scales and bones from juvenile Iguanodon in its stomach, while a tooth embedded in a South American pterosaur bone suggests that spinosaurs occasionally preyed on these flying archosaurs. Spinosaurus was likely to have been a generalized and opportunistic predator, possibly a Cretaceous equivalent of large grizzly bears, being biased toward fishing, though it undoubtedly scavenged and took many kinds of small-to medium-sized prey.

In popular culture

Spinosaurus has long been depicted in popular books about dinosaurs, although only recently has there been enough information about spinosaurids for an accurate depiction to be made. Traditionally, it has been restored as a generalized upright theropod with a sail on its back, after an influential 1955 skeletal reconstruction by Lapparent and Lavocat.

Spinosaurus was featured as the main antagonist in the 2001 film Jurassic Park III. It was portrayed as larger and more powerful than Tyrannosaurus, in a scene depicting a battle between the two resurrected predators where Spinosaurus emerges victorious by snapping the tyrannosaur's neck. In reality, no such battle could ever have taken place while the species were still extant, since Spinosaurus and Tyrannosaurus lived thousands of miles and millions of years apart.

After appearing in Jurassic Park III, Spinosaurus was featured in a wide variety of merchandise related to the Jurassic Park films, including a number of video games such as Jurassic Park: Operation Genesis from Vivendi Universal. Spinosaurus was also featured in the television documentary The Lost Dinosaurs of Egypt, in which it was seen wading through the marshlands of Cretaceous Egypt.

References

1. ^ dal Sasso, C. (2006). "New information on the skull of the enigmatic theropod Spinosaurus, with remarks on its sizes and affinities". Journal of Vertebrate Paleontology. 25 (4): 888–896. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
2. Molnar, Ralph E. (1990). "Carnosauria". The Dinosauria (1st ed.). Berkeley: University of California Press. pp. 169–209. ISBN 0-520-06727-4. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |editors= ignored (|editor= suggested) (help)
3. ^ Holtz, Jr., T.R., Molnar, R.E, and Currie, P.J. (2004). "Basal Tetanurae". The Dinosauria (second edition). University of California Press. pp. 71–110. ISBN 0-520-24209-2.{{cite book}}: CS1 maint: multiple names: authors list (link)
4. Rauhut, O.W.M. (2003). "The interrelationships and evolution of basal theropod dinosaurs". Special Papers in Palaeontology. 69: 1–213. {{cite journal}}: Check date values in: |year= (help)CS1 maint: year (link)
5. ^ Stromer, E. (1915). "Wirbeltier-Reste der baharije-Stufe (unterstes Cenoman).3. Das Origianl des Theropoden Spinosaurus aegyptiacus nov. gen. et nov. spec". Abhandlungen der Königlich Bayerischen Akademie der Wissenschaften Mathematisch-physikalische Klasse Abhandlung (in German). 28: 1–32. Cite error: The named reference "Stromer15" was defined multiple times with different content (see the help page).
6. Stromer, E. (1934). "Ergebnisse der Forschungsreisen Prof. E. Stromers in den Wüsten Ägyptens. II. Wirbeltierreste der Baharîje-Stufe (unterstes Cenoman). 13. Dinosauria". Abhandlungen der Bayerischen Akademie der Wissenschaften Mathematisch-naturwissenschaftliche Abteilung, Neue Folge (in German). 22: 1–79.
7. Sereno, P.C. (1998). "A long-snouted predatory dinosaur from Africa and the evolution of spinosaurids". Science. 282: 1298–1302. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
8. ^ Russell, D.A. (1996). "Isolated dinosaur bones from the Middle Cretaceous of the Tafilalt, Morocco". 18 (2–3): 349–402. {{cite journal}}: Cite journal requires |journal= (help); Unknown parameter |Journal= ignored (|journal= suggested) (help)
9. ^ Buffetaut, E & Ouaja, M (2002) A new specimen of Spinosaurus (Dinosauria, Theropoda) from the Lower Cretaceous of Tunisia, with remarks on the evolutionary history of the Spinosauridae. Bulletin de la Société Géologique de France 173 415-421; DOI: 10.2113/173.5.415
10. von Huene, F. R. (1926). "The carnivorous saurischia in the Jura and Cretaceous formations principally in Europe." Rev. Mus. La Plata, 29, 35-167
11. Glut, D.F. (1982). The New Dinosaur Dictionary. Citadel Press, Secaucus, New Jersey, 226-228. ISBN 0-8065-0782-9
12. ^ Paul, G.S. (1988). Predatory Dinosaurs of the World. New York: Simon and Schuster. 464 pp.
13. Bailey, Jack Bowman (1997). "Neural spine elongation in dinosaurs: sailbacks or buffalo-backs?". Journal of Paleontology. 71 (6): 1124–1146.
14. Halstead, L.B. (1975). The Evolution and Ecology of the Dinosaurs. London: Peter Lowe. pp. 1–116. ISBN 0856540188.
15. Buffetaut, E., D. Martill & F. Escuillié (2004). "Pterosaurs as part of a spinosaur diet." Nature, 430: 33. doi:10.1038/430033a
16. Glut, Donald F. (2000). "Spinosaurus". Dinosaurs: The Encyclopedia. 1st Supplement. Jefferson, North Carolina: McFarland & Company, Inc. pp. 329–333. ISBN 0-7864-0591-0.

External links

• Spinosaurus in the Dino Directory
• See entry on Spinosaurus at DinoData (registration required, free)
• The Biggest Carnivore: Dinosaur History Rewritten
• Spinosaurus Jaws
• Discover Magazine

• Cretaceous dinosaurs
• Spinosaurids
• African dinosaurs
• Jurassic Park species