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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. It was first known from Egyptian remains discovered in the 1910s and described by German paleontologist Ernst Stromer. The original remains were destroyed in World War II, but additional skull material has come to light in recent years.

The distinctive "spines" of Spinosaurus, which were long extensions of the vertebrae, grew up to 2 metres (6.6 ft) 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 recent estimates, it is the largest of all known carnivorous dinosaurs, even larger than Tyrannosaurus rex and Giganotosaurus; these estimates suggest that it was 16 - 18 meters in length (52.5 - 59.1 ft), around 6 meters tall (20 ft), and 9 tonnes (9.9 tons) in weight, although these figures have not been universally accepted.

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 2005 show that it had one of the longest skulls of any carnivorous dinosaur, estimated at about 1.75 meters long (5.7 ft). The skull had a narrow snout filled with conical teeth that lacked serrations, not unlike what is seen in other spinosaurids. A small crest was 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. 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 Baryonyx from southern England, Irritator and Angaturama (probably synonymous with Irritator) from Brazil, Suchomimus from Niger in central Africa, and possibly Siamosaurus, which is 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 in recent papers.

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 the Theropod Database and Dal Sasso et al, 2005.

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 from Tunisia which is very similar to existing material of S. aegyptiacus.

MSNM V4047, described by Cristiano Dal Sasso of the Civic Natural History Museum in Milan and his colleagues in 2005, is estimated to have been around 16-18 meters in length and weighed around 7 to 9 tonnes (7.7 to 9.9 tons). The massive skull is estimated at 1.75 meters long (5.74 ft). The fossils consist of premaxillae, partial maxillae, and partial nasals, which together measure 988 millimeters long (3.24 ft).

UCPC-2, also described by Dal Sasso et al. in 2005, 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 been a top contender for longest and 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 2005. Both Friedrich von Huene and Donald F. Glut, decades apart, 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, Gregory S. Paul also listed it as the longest theropod at 15 meters (50 feet), but gave a lower mass estimate. Recent estimates, based on new specimens, list Spinosaurus at 16 - 18 metres (53.3 to 60 feet) long and 7 - 9 tonnes in weight (7.7 to 9.9 tons). At least one unpublished survey, suggested that Spinosaurus reached sizes of 12 - 19 tonnes 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.

François Therrien and Donald Henderson, in a recent paper using scaling based on skull length, have challenged previous estimates, finding the length too great and the weight too small. Their estimates include a length of 12.6 to 14.3 meters (41.3 to 47.0 ft) and a mass of 12.0 to 20.9 tonnes (13.2 to 23.0 tons). Their study has been criticized for the choice of large theropods used for comparison (most of the skeletons of large theropods used to set the initial equations are of tyrannosaurids and carnosaurs, which have a different build than spinosaurids) and for issues relating to their spinosaurid skull reconstructions. Resolution awaits more complete remains.

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 including heat regulation and display. In addition, such a prominent feature on its back could also make it appear larger than it was, intimidating other animals.

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.

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.

Finally, it is quite possible that the sail combined 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.

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.

Posture

Although traditionally depicted as a biped, Spinosaurus has been suggested as at least an occasional quadruped since the early 1980s. This has been bolstered by the discovery of Baryonyx, a relative with robust arms. Bailey (1997) was sympathetic to a possible quadrupedal posture, leading to new restorations of it as such. This hypothesis has fallen out of favor, at least as a typical gait. Spinosaurids may have crouched in a quadrupedal posture, though.

Paleoenvironment

The environment inhabited by Spinosaurus is only partially understood, and covers a great deal of northern Africa. Those that lived in what is now Egypt, for example, may have contended with shoreline conditions on tidal flats and channels, living in mangrove forests alongside similarly large dinosaurian predators Bahariasaurus and Carcharodontosaurus, giant titanosaur sauropod Paralititan, smaller titanosaur Aegyptosaurus, 10 meter long (33 ft) crocodilian Stomatosuchus, and the coelacanth Mawsonia.

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, such a battle could never 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. (2005). "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. ^ Mortimer, M. (2004). "Megalosauroidea". The Theropod Database. University of Washington. Retrieved 2007-07-04. {{cite web}}: Cite has empty unknown parameter: |coauthors= (help)
10. 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
11. von Huene, F. R. (1926). "The carnivorous saurischia in the Jura and Cretaceous formations principally in Europe." Rev. Mus. La Plata, 29, 35-167
12. ^ Glut, D.F. (1982). The New Dinosaur Dictionary. Citadel Press, Secaucus, New Jersey, 226-228. ISBN 0-8065-0782-9 Cite error: The named reference "DFG82" was defined multiple times with different content (see the help page).
13. ^ Paul, G.S. (1988). Predatory Dinosaurs of the World. New York: Simon and Schuster. 464 pp.
14. Mortimer, Mickey (2001-07-23). "Re: Spinosaurus weight". Dinosaur Mailing List. Retrieved 2007-07-04.
15. Mortimer, Mickey (2003-07-21). "And the Largest Theropod Is..." Dinosaur Mailing List. Retrieved 2007-07-04.
16. Mortimer, Mickey (2006-12-23). "Theropod Database Christmas update". Dinosaur Mailing List. Retrieved 2007-07-04.
17. Therrien, F. (2007). "My theropod is bigger than yours...or not: estimating body size from skull length in theropods". Journal of Vertebrate Paleontology. 27 (1): 108–115. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
18. Mortimer, Mickey (2007-03-25). "Comments on Therrien and Henderson's new paper". Dinosaur Mailing List. Retrieved 2007-07-04.
19. ^ Bailey, Jack Bowman (1997). "Neural spine elongation in dinosaurs: sailbacks or buffalo-backs?". Journal of Paleontology. 71 (6): 1124–1146.
20. Halstead, L.B. (1975). The Evolution and Ecology of the Dinosaurs. London: Peter Lowe. pp. 1–116. ISBN 0856540188.
21. Buffetaut, E., D. Martill & F. Escuillié (2004). "Pterosaurs as part of a spinosaur diet." Nature, 430: 33. doi:10.1038/430033a
22. ^ Glut, Donald F. (2000). "Spinosaurus". Dinosaurs: The Encyclopedia. 1st Supplement. Jefferson, North Carolina: McFarland & Company, Inc. pp. 329–333. ISBN 0-7864-0591-0.
23. Charig, Alan J. (1997). "Baryonyx walkeri, a fish-eating dinosaur from the Wealden of Surrey". Bulletin of the Natural History Museum, Geology Series. 53 (1): 11–70. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
24. Smith, J.B. (2001). "A Giant sauropod dinosaur from an Upper Cretaceous mangrove deposit in Egypt". Science. 292 (5522): 1704–1706. doi:10.1126/science.1060561. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)

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
• Dinosaurs of Africa
• Jurassic Park species