Gorgosaurus

Live image of Gorgosaurus libratus

• North America

• Gorgosaurus libratus

Gorgosaurus (Greek: " impetuous lizard", from γοργός / gorgos " impetuous " or "terrible" and σαῦρος / saurus " lizard" ) was a theropod dinosaur from the family of tyrannosaurids, the front of about 76 to 72 million years in the Upper Cretaceous (late Campanian ) in western North America lived. Fossil remains have been found in the Canadian province of Alberta and possibly the U.S. state of Montana. Currently is only recognized by this genus a kind, the type species Gorgosaurus libratus.

Like most known tyrannosaurids, Gorgosaurus was a bipeder predator that weighed more than a ton as an adult animal, and dozens wearing of large, sharp teeth in the jaw, while the two -fingered arms were small in proportion. Gorgosaurus was closely related to the very similar Albertosaurus; both genera are separated only on the basis of slight differences in the teeth and skull bones. Some experts consider Gorgosaurus libratus for Albertosaurus -Art - According to this view, a juvenile Gorgosaurus would synonym of this genus.

Gorgosaurus lived in a lush floodplain along the Western Interior Seaway, an arm of the sea, who shared in the Upper Cretaceous North America into two halves. As a Spitzenprädator Gorgosaurus was at the top of the food chain and hunted probably the frequent Ceratopsiden and Hadrosauriden. In some areas, Gorgosaurus lived with Daspletosaurus, other tyrannosaurids. Although these animals were approximately the same size, there is evidence that both classes occupied different ecological niches. Gorgosaurus is the most commonly found Tyrannosauride - the numerous fossils allow scientists to draw conclusions about the biology of tyrannosaurids, such as on the individual development ( ontogeny ).

• 4.1 Coexistence with Daspletosaurus
• 4.2 ontogeny and population biology

Description

Gorgosaurus reached about the size of Albertosaurus and Daspletosaurus. Adult animals were eight or nine feet long and weighed probably more than 2.4 tons. The largest skull measures 99 centimeters in length and found is only slightly smaller than that of Daspletosaurus. Like other tyrannosaurids of the skull in relation to the body was large, with chambers in the skull bones and large openings skull ( cranial window) reduced its weight. Albertosaurus and Gorgosaurus have relative longer and flatter skulls than Daspletosaurus and other tyrannosaurids. The snout was blunt and the paired nasal bone ( nasal ) and the paired parietal ( parietal ) was fused along the midline of the skull, as with all other members of the family. The eye socket ( orbital window) was round and thus differed from the oval to keyhole - like forms in other tyrannosaurids. Similar to Albertosaurus and Daspletosaurus extends in front of each eye, a high ridge from the lacrimal bone ( lacrimal ). Gorgosaurus is distinguished from Albertosaurus basis of differences in the bones surrounding the brain.

The teeth of Gorgosaurus were typical of all known tyrannosaurids. The eight teeth of the premaxillary bone ( premaxilla ) at the front snout were compared to the remaining teeth small, tightly packed and in section "D " shaped. The remaining teeth were oval in cross-section, and blade-shaped not like most other theropods. In addition to the eight teeth of the premaxillary bone Gorgosaurus had 26 to 30 teeth in the upper jaw and 30 to 34 teeth in the lower jaw. Gorgosaurus has thus about as many teeth as Albertosaurus and Daspletosaurus, Tarbosaurus but less than or Tyrannosaurus.

As with all tyrannosaurids Gorgosaurus 's blueprint is characterized by a large head, sitting on a "S " shaped neck. In contrast to the large head, the arms were very small. The hands had only two toes, although a third member was detected in the metacarpal in some finds - a rudiment of the third finger, as it had other theropods. The hind legs of the tyrannosaurids were in proportion to the body longer than other theropods. The longest known Gorgosaurus femur (femur ) measures 105 centimeters. In several smaller specimens, however, the shinbone ( tibia) was longer than the femur - a ratio, as it is often found in fast-running animals. The two bones were of approximately equal length for the largest found skeletons.

System

Within the tyrannosaurids Gorgosaurus is counted to the subfamily Albertosaurinae - together with the closely related geologically slightly younger Albertosaurus. These two species are the only definitive representatives of Albertosaurinae that have been described so far - though perhaps there are other, as yet undescribed species. All other tyrannosaurids are classified in the second subfamily, the Tyrannosaurinae. Compared with the tyrannosaurines albertosaurines is distinguished by a slimmer physique with proportionately smaller, flatter skulls and longer lower leg and foot bones.

The significant similarities between Gorgosaurus and Albertosaurus sarcophagus libratus meant that many experts suggested to combine the two genres - so Gorgosaurus was sometimes identified as a juvenile synonym of Albertosaurus. Albertosaurus was named Gorgosaurus before and would thus be the valid name, if it is one and the same genus. The paleontologist William Diller Matthew and Barnum Brown doubted the distinction of two genera in the year 1922. Gorgosaurus libratus was remapped by Dale Russell ( 1970), formally the Albertosaurus (as Albertosaurus libratus ), and many authors followed this assumption. Would Gorgosaurus actually a subspecies of Albertosaurus, which would greatly expand the geographical and chronological distribution of the latter. Other experts distinguish between the two genres. So says The Canadian paleontologist Philip Currie that there are so many anatomical differences between Albertosaurus and Gorgosaurus are between Daspletosaurus and Tyrannosaurus like that are almost always listed as separate genera. He further noted that undescribed tyrannosaurids from Alaska, New Mexico and other sites in North America could help to clarify the situation.

History of discovery and naming

Gorgosaurus libratus was first described by Lawrence Lambe in 1914. The name is derived from the ancient Greek words γοργος / gorgos ( " impetuous ", " fast" ) and σαυρος / derived saurus ( "lizard "). The Artepitheth libratus is the past participle of the Latin verb librare what " balance " means.

The holotype of Gorgosaurus libratus (NMC 2120) is an almost complete, connected with a skull skeleton, which was discovered in 1913 by Charles Sternberg. This skeleton was the first discovery of a tyrannosaurids in which the hand is completely preserved. The find was made in the Dinosaur Park Formation of Alberta and is now in the Canadian Museum of Nature in Ottawa. Collector of the American Museum of Natural History in New York City have discovered along the Red Deer River in Alberta at the same time hundreds of spectacular dinosaur finds, including four complete skull of Gorgosaurus libratus, three of which were associated with skeletons. Matthew and Brown described four of these findings in 1923.

In addition, Matthew and Brown described a fifth skeleton (AMNH 5664), had the Sternberg collected in 1917 and then sold to the American Museum of Natural History. It resembled other Gorgosaurus skeletons, but had a thinner, lighter skull and longer leg proportions. Many sutures were not fused between the bones. Although Matthew and Brown noted that these features are characteristic of juvenile animals, yet they described based on this skeleton the new way Gorgosaurus Sternbergi. Today's paleontologists regard this skeleton in any case as a juvenile specimen of Gorgosaurus libratus. Dozens of other finds were excavated from the Dinosaur Park Formation and are exhibited in various museums in the United States and Canada. Gorgosaurus libratus is therefore in the fossil record most emerging Tyrannosauride. The finds cover almost all ages.

In 1856, Joseph Leidy described two tyrannosaurid teeth of the premaxillary bone ( premaxilla ) from Montana. Although there was no evidence of the appearance of the animal, the teeth were large and robust enough Leidy gave them the name Deinodon. Matthew and Brown wrote in 1922 that these teeth from those of Gorgosaurus are indistinguishable - but as additional skeletal material was not available, it avoided the researchers to classify Deinodon as synonymous with Gorgosaurus. Although the Deinodon teeth see the teeth of Gorgosaurus very similar to the shape of tyrannosaurid teeth is very uniform, which is why you can not say with certainty to what class they belonged. Today Deinodon considered as a noun dubium ( dubious name). Various other tyrannosaurid skeletons from the Judith River Formation of Montana belong to Gorgosaurus, although it is unclear whether these findings were among Gorgosaurus libratus or to a new kind of policy. A specimen from Montana ( TCMI 2001.89.1 ), which is exhibited in the Children's Museum of Indianapolis, shows serious injuries and illnesses: So healed leg, rib and vertebral fractures were discovered. It was also found that the suffered the animal to osteomyelitis, an infectious inflammation of the bone marrow, leading to permanent loss of teeth in the lower jaw. A possible brain tumor was also available.

Newly allocated species

Various species have been erroneously attributed to Gorgosaurus in the 20th century. For younger rock strata (late Maastrichtian ) of the Hell Creek Formation of Montana comes a complete skull of a small tyrannosaurids ( CMNH 7541 ), the Charles Whitney Gilmore described in 1946 as Gorgosaurus lancensis. This species was renamed by Bob Bakker and others in Nanotyrannus in 1988. Today, most paleontologists believe that it was at Nanotyrannus a juvenile specimen of Tyrannosaurus rex. Evgeny Maleev described in 1955 two small tyrannosaurid skeletons (PIN 553-1 and PIN 552-2 ) from the Nemegt Formation of Mongolia as Gorgosaurus Gorgosaurus lancinator and novojilovi. Although named Kenneth Carpenter 1992, the smaller skeleton in Maleevosaurus novojilovi to be both skeletons are today, however, as a juvenile specimen of Tarbosaurus bataar.

Paleobiology

Coexistence with Daspletosaurus

In the Dinosaur Park Formation, Gorgosaurus lived with Daspletosaurus, a rarer tyrannosaurines genus. This is one of the few examples of a coexistence of two tyrannosaurids. In modern predator guilds similar large predators occupy different ecological niches through which the competition is limited. To what extent this was the case with the tyrannosaurs of the Dinosaur Park Formation, is not sufficiently clarified. In 1970, suspected Dale Russell, the frequent Gorgosaurus could have chased the nimble hadrosaurs, while the heavy -built Daspletosaurus could have the rarer and more difficult to hunting Ceratopsia and Ankylar preferred. In any case, the digested remains of a juvenile Hadrosauriers have been preserved in the abdominal cavity in a Daspletosaurus skeleton (OTM 200 ) from the same time deposited Two Medicine Formation of Montana.

Unlike some other groups of dinosaurs, neither yet Daspletosaurus Gorgosaurus was more common than the other one in certain altitudes. Nevertheless, Gorgosaurus appears to be more common in the more northern formations like the Dinosaur Park Formation, while Daspletosaurus is more common in the south. The same pattern is seen in other groups of dinosaurs; so chasmosaurine ceratopsians and hadrosaurs hadrosaurine in the Two Medicine Formation of Montana and western North America are more common during the Campanian, while the Centrosaurinae and Lambeosaurinae dominated the northern latitudes. Holtz suspected because of this pattern that hadrosaurines, Chasmosaurinen and tyrannosaurines preferred similar habitats. At the end of the late Maastrichtian tyrannosaurines such as Tyrannosaurus rex, hadrosaurines as Edmontosaurus and Triceratops Chasmosaurinen as in western North America were widespread, while albertosaurines and cents Rosa urines extinct and Lambeosaurinen were very rare.

Ontogeny and population biology

Researchers led by Gregory Erickson have calculated using the bone histology at different tyrannosaurid finds how old the animals were when they died. This allows to draw conclusions on the individual development ( ontogeny ). Like all tyrannosaurids Gorgosaurus also showed a very fast, about four years -ending growth that occurred after a very long Juvenilphase. During this growth phase Gorgosaurus reached maximum growth rate of 110 kilograms per year. This is slower than tyrannosaurines as Daspletosaurus and Tyrannosaurus, but comparable to Albertosaurus. Tyrannosaurid shared their habitat with theropods that were smaller by a multiple; However, it lacks predators, who were in their size between tyrannosaurids and small theropods. Since Gorgosaurus and other tyrannosaurids spent about half their lives in the juvenile stage, some researchers suspect that this niche was occupied by juvenile tyrannosaurids.

Paleoecology

All known skeletons of Gorgosaurus libratus come from the Dinosaur Park Formation, which is famous for its huge concentration of dinosaur fossils and was deposited in front of about 76 to 72 million years. At that time, North America was divided by an arm of the sea, the Western Interior Seaway, into two halves, while the Rocky Mountains began to rise in the wake of lara mix orogeny in the West. Large rivers flowed from the rising Rocky Mountains in the Western Interior Seaway in the east, where they were deposited sediments in flood levels along the coast, which today form the Dinosaur Park Formation among others. The climate was subtropical, pointing to periodic droughts, which led to mass deaths among big dinosaur herds, as can be seen in the numerous bonebeds the Dinosaur Park Formation. The vegetation was formed by conifers, ferns, tree ferns and angiosperms. The dinosaur fauna consisted of large herds of Ceratposiern and Hadrosauriden; other herbivores were Ornithomimosaurier, Therizinosaurier, Pachycephalosaurier, small ornithopods and Ankylar. Small carnivores such as Oviraptorosaurier, troodontids and Dromeosauriden hunted smaller prey than the huge tyrannosaurids Daspletosaurus and Gorgosaurus as.