||[Apr. 25th, 2006|11:17 pm]
Humphrey Bogart Fan Club
Spinosaurus sails were unusual, although other dinosaurs of the same time and area, namely the ornithopod Ouranosaurus and the sauropod Rebbachisaurus, developed a similar structure of their dorosal vertebrae. 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 its 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 problem of losing excess heat at higher temperatures than gaining it at lower. Sails of these dinosaurus 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 effectivly 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 dinosaurus were used for courtship, in a way similar to peacock's tail. If this was the case, the sails may have been brightly colored, but this is pure guesswork.
Intimidating device. The sail was possibly used to intimidate rivals or frighten enemies, making the animal look 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 normaly 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 threathened.