Spinosaurus

Spinosaurus (meaning 'spine lizard') was a theropod dinosaur genus that lived in what is now Egypt, from the Albian to early Cenomanian stages of the Cretaceous Period, about 95 to 93 million years ago. According to a study by dal Sasso et al. (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 15 to 17.4 metres (49.2 to 57.1 feet) long and reached weights up to 9 tons.^[1]

The distinctive "spines" of these animals (long extensions of the vertebrae) grew up to 2 m (6.6ft) long and were likely to have had skin connecting them, forming a sail-like structure, although some have suggested they were covered in muscle and formed a hump or ridge.

Spinosaurus provides the name of a family of dinosaurs, the Spinosauridae, of which other members include Angaturama (probably synonymous with Irritator), Baryonyx, Irritator, Suchomimus, and Siamosaurus.

Anatomy and morphology

Although Spinosaurus is well-known to dinosaur enthusiasts due to its unusual features, it is mostly known from remains that have been destroyed, aside from a few more recently discovered teeth and skull elements. Jaw and skull material published in 2006 show that it had one of the longest skulls of any carnivorous dinosaur, estimated by dal Sasso et al. at about 175 cm (5.7 ft).

Aside from its 'sail', notable characteristics of Spinosaurus include:

• A long, narrow snout, similar to other Spinosaurids and, like them, filled with conical teeth.
• One enlarged, hook-like claw on each of its front limbs, perhaps for catching fish.
• Relatively short legs and long 'arms', leading some paleontologists to suggest it may have been quadrupedal, rather than strictly bipedal (though it was undoubtedly capable of at least facultative bipedality).

Much of this is speculation based on Baryonyx and other spinosaurids, as no limb material has ever been attributed to Spinosaurus itself.

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 (1926) and Glut (1982) listed it as the most massive theropod in their surveys, at upwards of 6 tons in weight and 15 meters (50 feet) in length. Paul (1988) 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 described by dal Sasso et al. (2006), list Spinosaurus at 16 - 18 metres (53.3 to 60 feet) long and 7.5 - 9 tons in weight. At least one survey, as-yet unpublished, suggest that Spinosaurus reached sizes of 12 - 19 tons in weight. These high-end weight estimates were based on the fact that the vertebrae of Spinosaurus are unusually massive compared to theropods of comparable size (implying an extremely large overall mass), and that the holotype specimens are apparently sub-adult. [1] However the author of these estimates has recently reduced them to similar sizes suggested by dal Sasso et al. [2] [3]

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 purpose 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. 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, since things in nature rarely develop for a singular reason, 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.

Ecology and life history

Feeding ecology

It is unclear whether Spinosaurus was primarily a cursorial 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 more 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 (Paul, 1988).

Etymology and taxonomic history

Two species of Spinosaurus have been named: Spinosaurus aegyptiacus ("Egyptian spine lizard") and Spinosaurus marocannus ("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 [4].

Five partial specimens of Spinosaurus have been found, the first having been destroyed during World War II (luckily, 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.

• IPHG 1912 VIII 19 (Stromer, 1915) (destroyed during allied bombing in WWII)
  • Size: 17.4 m, 12-19 tons (subadult)
  • Material: (skull ~1.45 m) maxillary fragment, incomplete dentary (mandible ~1.34 m), nineteen teeth (62, 126 mm), two incomplete cervical vertebrae, seven dorsal vertebrae (190-210 mm), dorsal ribs, gastralia, eight caudal centra.
• CMN 50791 (Russell, 1996)
  • Material: mid cervical vertebra (195 mm), anterior dorsal neural arch, anterior dentary, mid dentary.
  • Note: holotype of Spinosaurus marocannus.
• MNHN SAM 124 (Taquet and Russell, 1998)
  • Size: ~17 m, ~11-18 tons (adult)
  • Material: (skull ~1.42 m) partial premaxillae, partial maxillae, vomers, dentary fragment.
• Office National des Mines nBM231 (Buffetaut and Ouaja, 2002)
  • Material: anterior dentary.
• MSNM V4047 (Dal Sasso et al., 2006)
  • Size: ~21 m, ~20-32 tons
  • Material: (skull ~1.75 m) premaxillae, partial maxillae, partial nasals

Rauhut (2003) 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, was rejected by dal Sasso and most other researchers.

Discovery

Originally found in the Bahariya Valley of Egypt in 1912, it was named by German paleontologist Ernst Stromer in 1915. Some of the 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.

In popular culture

Jurassic Park III

Spinosaurus achieved widespread fame as the main antagonist in Jurassic Park III. It is portrayed as larger, more powerful and more vicious than Tyrannosaurus, epitomized by a scene in which the two resurrected predators battle and Spinosaurus emerges victorious by snapping the rex's neck, establishing itself in the movie as the new main predator. In reality, no such battle could ever have taken place, since Spinosaurus and Tyrannosaurus lived thousands of miles and millions of years apart.

Spinosaurus did, however, share its habitat with two other theropods that equalled or exceeded T. rex in size: the massive carnosaur Carcharodontosaurus and the large but relatively lightweight abelisaur Deltadromeus. Although the three predators probably occupied different ecological niches, they may have occasionally come into conflict over prey or territory.

Others

Also, after being in Jurassic Park III, Spinosaurus was also featured in the Vivendi Universal game, "Jurassic Park: Operation Genesis".

Spinosaurus was also featured in the TV documentary "The Lost Dinosaurs of Egypt".

References

Wikipedia information about Spinosaurus This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Spinosaurus". It may not have been reviewed by professional editors (see full disclaimer). Help contribute to Americola and edit this article.