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Categories: Dinosaurs
Gorgosaurus, meaning "fierce lizard", is a genus of tyrannosaurid theropod dinosaur that lived in western North America between 80 and 73 million years ago, during the Late Cretaceous Period. Like most known tyrannosaurids, Gorgosaurus was a multi-ton bipedal predator equipped with dozens of large, sharp teeth; it also bore tiny two-fingered forelimbs typical of its close relatives. Although relatively large for a theropod, Gorgosaurus was much smaller than its more famous relative Tyrannosaurus. It was first described by paleontologist Lawrence Morris Lambe, in 1914. Since then more than 20 Gorgosaurus skeletons have been recovered, making it the best-represented tyrannosaurid in the fossil record. In some areas, it coexisted with another tyrannosaurid, Daspletosaurus, though there is some evidence of niche differentiation between the two. As an apex predator, Gorgosaurus was at the top of the food chain, probably preying on large dinosaurs like the ceratopsid Centrosaurus and the hadrosaur Hypacrosaurus. While clearly a large and fearsome animal, Gorgosaurus was nonetheless much smaller than the truly gigantic tyrannosaurids like Tarbosaurus and Tyrannosaurus. It was around the same size as Daspletosaurus, which it appears to have coexisted with. Adults reached 7 to 8 metres (27 to 30 ft) from snout to tail, with an estimated weight of 2.5 tonnes (2.75 short tons).[1] It had a massive skull almost a meter (39 in) long, perched on a short S-shaped neck. Wide openings in the skull (fenestrae) reduced the weight of the head and provided space for muscle attachment and sensory organs. Gorgosaurus had a more circular orbit than any other tyrannosaurid. It bore large curved teeth, tiny two-fingered front limbs, and powerful legs. Compared to the other tyrannosaurids, Gorgosaurus is most similar to its very close relative Albertosaurus.[1] Gorgosaurus is a member of the theropod family Tyrannosauridae, in the subfamily Albertosaurinae. Its closest relative is the slightly younger Albertosaurus sarcophagus.[2] These two species are the only described albertosaurines, although other undescribed species may exist.[3] The species G. libratus, the only species of Gorgosaurus currently recognized, was reassigned to Albertosaurus by Russell in his extensive review of the Tyrannosauridae in 1970,[4] which many subsequent authors followed.[5][6] However, recent work done by Thomas Holtz suggest that enough differences exist between G. libratus and the other Albertosaurus species to justify the original genus name of Gorgosaurus.[7] Holtz found Appalachiosaurus to be an albertosaurine in 2004,[7] but his more recent unpublished work locates it just outside Tyrannosauridae,[8] in agreement with other authors.[9] The other major subfamily of tyrannosaurids is the Tyrannosaurinae, including Daspletosaurus torosus, Tarbosaurus bataar and Tyrannosaurus rex. Compared to these robust tyrannosaurines, albertosaurines had slender builds, with proportionately smaller skulls and longer bones of the lower leg (tibia) and feet (metatarsals and phalanges).[10][2] Gorgosaurus was first described by paleontologist Lawrence Morris Lambe in 1914, who named it "fierce lizard" from the Greek gorgos/γορργος meaning "terrible" or "fierce" and saurus/σαυρος meaning "lizard".[11] Fossilized tyrannosaurid teeth of the Late Cretaceous of Montana, described as Deinodon by paleontologist Joseph Leidy in 1856, are likely to belong to Gorgosaurus, though it is virtually impossible to distinguish between different tyrannosaurid species based on tooth characteristics alone, so Deinodon is today considered a nomen dubium. Gorgosaurus is known from more complete fossil material than any other tyrannosaurid, with over 20 skeletons recovered. However confirmed material is thus far restricted to the upper Dinosaur Park Formation of the late Campanian of Alberta, though probable fragmentary remains have been found in the Two Medicine and Judith River Formations of Montana and Fruitland and lower Kirtland Formations of New Mexico. Although it has been suggested that Gorgosaurus was a scavenger, its co-existence with the similarly sized tyrannosaurid Daspletosaurus casts doubt on this theory. Another hypothesis proposes that Gorgosaurus, which was rather lean for a tyrannosaurid, actively hunted fleet-footed animals such as duckbills and ornithomimids ('ostrich-mimic' dinosaurs). According to this proposition, the more troublesome ceratopsians and ankylosaurians (horned and heavily armoured dinosaurs) would have been left to Daspletosaurus. In the late Campanian of North America, Gorgosaurus was a contemporary of Daspletosaurus, also a tyrannosaurid. This is one of the few examples of two tyrannosaur genera coexisting. In modern predator guilds, similarly-sized predators are separated into different ecological niches by anatomical, behavioral or geographical differences that limit competition.[12] Several studies have attempted to explain niche differentiation in Gorgosaurus and Daspletosaurus. Paleontologist Dale Russell hypothesized that the more common Gorgosaurus may have preyed on the abundant hadrosaurs of the time, while the less common Daspletosaurus may have specialized on the less prevalent but better-defended ceratopsids, which may have been more difficult to hunt.[4] However, a specimen of Daspletosaurus (OTM 200) from the Two Medicine Formation preserves the digested remains of a juvenile hadrosaur in its gut region.[13] The higher and broader muzzles of tyrannosaurines like Daspletosaurus are mechanically stronger than the lower snouts of albertosaurines like Gorgosaurus, although tooth strengths are similar between the two groups. This may indicate a difference in feeding mechanics or diet.[14] Other authors have suggested that competition was limited by geographical separation. Unlike some other groups of dinosaurs, there appears to be no correlation with distance from the sea. Neither Gorgosaurus nor Daspletosaurus was more common at higher or lower elevations than the other.[12] However, while there is some overlap, Gorgosaurus appears to be more common at northern latitudes, with species of Daspletosaurus more abundant to the south. The same pattern is seen in other groups of dinosaurs. Chasmosaurine ceratopsians and hadrosaurine hadrosaurs are also more common in the Two Medicine Formation and in southwestern North America during the Campanian. Thomas Holtz has suggested that this pattern indicates shared ecological preferences between tyrannosaurines, chasmosaurines and hadrosaurines. Holtz notes that, at the end of the later Maastrichtian stage, tyrannosaurines like Tyrannosaurus rex, hadrosaurines and chasmosaurines like Triceratops were widespread throughout western North America, while albertosaurines and centrosaurines went extinct, and lambeosaurines were very rare.[7]
Contents
[edit] Description
[edit] Classification and systematics
[edit] Discovery and naming
[edit] Paleobiology
[edit] References
[edit] External links
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