Gorgosaurus (meaning "fierce lizard") is an extinct genus of theropod and carnivorous dinosaur that reached 8 to 9 meters (26 to 30 feet) in length, and weighed 2.8-3.4 tonnes. It was first described by paleontologist Lawrence Morris Lambe in 1914, and has been found in western Canada and the United States. It lived about 76-75 million years ago in the late Cretaceous period.
Over 20 Gorgosaurus skeletons have been recovered, making it the most well-represented tyrannosaurid in the fossil record. Generally similar to Tyrannosaurus and most other large tyrannosaurids (such as Daspletosaurus, and Albertosaurus), Gorgosaurus can be described as having a massive head, 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.
Although it has been suggested that Gorgosaurus was a scavenger, its co-existence with the similarly sized, but more robust 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 and Gorgosaurus would have hunted on less armored hadrosaurs. An apex predator, it was at the top of the food chain.
For years, the species Gorgosaurus libratus (the only species of Gorgosaurus currently recognized) was assigned to the Albertosaurus genus. However, recent work done by paleontologists suggest that enough differences exist between G. libratus and the other Albertosaurus species, to justify the original genus name of Gorgosaurus.
Gorgosaurus libratus was first described by Lawrence Lambe in 1914.[1][2] Its name is derived from the Greek γοργος/gorgos ("fierce" or "terrible") and σαυρος/saurus ("lizard").[3] The type species is G. libratus; the specific epithet "balanced" is the past participle of the Latin verb librare, meaning "to balance".[2]
The holotype of Gorgosaurus libratus (NMC 2120) is a nearly complete skeleton associated with a skull, discovered in 1913 by Charles M. Sternberg. This specimen was the first tyrannosaurid found with a complete hand.[1] It was found in the Dinosaur Park Formation of Alberta and is housed in the Canadian Museum of Nature in Ottawa.[4] Prospectors from the American Museum of Natural History in New York City were active along the Red Deer River in Alberta at the same time, collecting hundreds of spectacular dinosaur specimens, including four complete G. libratus skulls, three of which were associated with skeletons. Matthew and Brown described four of these specimens in 1923.[5]
Type specimen of Gorgosaurus sternbergi (AMNH 5664), now recognized as a juvenile Gorgosaurus libratus
Matthew and Brown also described a fifth skeleton (AMNH 5664), which Charles H. Sternberg had collected in 1917 and sold to their museum. It was smaller than other Gorgosaurus specimens, with a lower, lighter skull and more elongate limb proportions. Many sutures between bones were unfused in this specimen as well. Matthew and Brown noted that these features were characteristic of juvenile tyrannosaurids, but still described it as the holotype of a new species, G. sternbergi.[5] Today's paleontologists regard this specimen as a juvenile G. libratus.[6][4] Dozens of other specimens have been excavated from the Dinosaur Park Formation and are housed in museums across the United States and Canada.[7][4]G. libratus is the best-represented tyrannosaurid in the fossil record, known from a virtually complete growth series.[6][8]
Gorgosaurus libratus specimen (AMNH 5458)
In 1856, Joseph Leidy described two tyrannosaurid premaxillary teeth from Montana. Although there was no indication of what the animal looked like, the teeth were large and robust, and Leidy gave them the name Deinodon.[9] Matthew and Brown commented in 1922 that these teeth were indistinguishable from those of Gorgosaurus, but in the absence of skeletal remains of Deinodon, opted not to synonymize the two genera.[10] Although Deinodon teeth are very similar to those of Gorgosaurus, tyrannosaurid teeth are extremely uniform, so it cannot be said for certain which animal they belonged to. Deinodon is regarded as a nomen dubium today.[7][8] Several tyrannosaurid skeletons from the Judith River Formation of Montana probably belong to Gorgosaurus, although it remains uncertain whether they belong to G. libratus or a new species.[4] One specimen from Montana (TCMI 2001.89.1), housed in the Children's Museum of Indianapolis, shows evidence of severe pathologies, including healed leg, rib, and vertebral fractures, osteomyelitis (infection) at the tip of the lower jaw resulting in permanent tooth loss, and possibly a brain tumor.[11][12]
Description[]
G. libratus adult and subadult with a human for scale
Gorgosaurus was smaller than Tyrannosaurus or Tarbosaurus, closer in size to Albertosaurus and Daspletosaurus. Adults reached 8 to 9.3 m (26 to 31 ft) from snout to tail and a body weight of around 3 tonnes. The largest known skull measures 99 cm (39 in) long, just slightly smaller than that of Daspletosaurus. As in other tyrannosaurids, the skull was large compared to its body size, although chambers within the skull bones and large openings (fenestrae) between bones reduced its weight. Gorgosaurus has a proportionally shorter skull than Albertosaurus, Daspletosaurus and other tyrannosaurids. The end of the snout was blunt, and the nasal and parietal bones were fused along the midline of the skull, as in all other members of the family. The eye socket was circular rather than oval or keyhole-shaped as in other tyrannosaurid genera. A tall crest rose from the lacrimal bone in front of each eye, similar to Albertosaurus and Daspletosaurus. Differences in the shape of bones surrounding the brain set Gorgosaurus apart from Albertosaurus.
Classification and systematics[]
Restoration of a sub-adult individual
Gorgosaurus is often considered an albertosaurine, which is supporter by Thomas Holtz Jr., who has presented unpublished materials that reconsider it from a basal tyrannosauroid outside Tyrannosauridae then to an albertosaurine tyrannosaurid. Similarity between it and Albertosaurus have led to confusion and the occasionally synonymization. However, both have been realized as distinct. Loewen et al. (2013) conclude:
A graph showing the hypothesized growth curves (body mass versus age) of four tyrannosaurids. Gorgosaurus is shown in blue.
Gregory Erickson and colleagues have studied the growth and life history of tyrannosaurids using bone histology, which can determine the age of a specimen when it died.
Most Gorgosaurus are known from the Campanian-aged Dinosaur Park Formation. Many vertebrates are known from here, with fish swimming the rivers and dinosaurs roaming the land. It lived with Daspletosaurus. One Saurornitholestes dentary bears the bites of a juvenile tyrannosaur, possibly being of Gorgosaurus.
In 2012 it was found Gorgosaurus has a bite force of ~42,000 newtons.
Life History[]
Gregory Erikson et. al. have been studying the life history of tyrannosaurids based on bone histology determining age in life. He plotted the age and weights of tyrannosaurids on a graph to determine the growth rate of different tyrannosaur genera. The graph tells scientists that juvenile tyrannosaurs underwent massive growth spurts, for about four years, in the middle of their lives. After the individuals hit sexual maturity, they then tremendously slowed their growth. Gorgosaurus showed a faster growth rate due to having a higher mature weight. Gorgosaurus' maximum growth rate is about 50 kilograms (110 pounds) per year. The lack of predators that allowed for it to grow large suggests the predator niche was inhabited by small juveniles, seen in Komodo dragons. There is no evidence for gregarious behaviour.
Paleopathology[]
Several pathologies from NMC 2120 are recorded, including: the third right dorsal rib, healed fractures of the 13th and 14th gastralia and left fibula, a 4th metatarsal with rough exostoses in the middle and far end, a deformed third phalanx of the right toe and a small and amorphous claw. Three may have been received via a single confrontation with another dinosaur. TMP91.36.500 bears craniofacial bites, a healed dentary fracture and a mushroom-like hyperostosis on the right pedal phalanx and a thoroughly healed fracture of the right fibula. Such a hyperostosis may be similar to a similar growth an unidentified ornithomimosaur suffered. It is preserved in the death pose. Another specimen bears a poorly-healed fracture on the right fibula. Bruce Rothschild et al. (2001) tested 54 foot bones for stress fractures, but none were recovered. The specimen "Ruth" was the first dinosaur to have evidence of a brain tumour, which would have weakened motor skills and caused the individual to fall down often.
Notable Specimens[]
TCMI 2001.89.1[13] "Ruth": A specimen unveiled at the Museum of Ancient Life at Thanksgiving Point, Utah
"Ruth" in the lobby of the Museum of Ancient Life.
on June 22, 2018 and presented by paleontologist Rick Hunter. The skull is 90% complete and the skeleton is about 75% complete, discovered by the Linster family's son, 14 at the time, on their ranch in Montana in 1993 or 1997. The specimen was photographed, documented and catalogued by the family over the next 15 summers. The skull was discovered by the father, Cliff, and took 3 years to fully excavate. The skull was nearly intact and very well preserved, allowing molds to be taken of the cranium which revealed that this individual suffered a brain tumour, being the first evidence of this in dinosaurs. This affliction likely weakened motor skills and caused the animal to have fell down often. The specimen was initially supposed to have gone to a university, but the family insisted it go to a local museum because they wanted "non-traditional" paleontologists and locals to explore deep time. The specimen resides in the lobby of the museum. Ruth also bears a shattered shoulder, broken fibula, crushed caudals and broken ribs.
Gorgosaurus is considered by some scientists to be the same as Albertosaurus. This dinosaur looked like a smaller, slightly less muscular version of Tyrannosaurus. As an early member of the tyrannosaur family, Gorgosaurus was the final design for the large meat-eating dinosaurs. It had only two fingers on its hands, which were at the end of short arms. It had long legs and a wide skull with lots of power in its bite.
Gorgosaurus was named based on material that is now being disputed as requiring a genus separate from Albertosaurus.
Gorgosaurus ("fierce lizard") was a tyrannosaur, or tyrant dinosaur, It was a very close relative of Tyrannosaurus- although Gorgosaurus was a little smaller and lived somewhat earlier. The tyrant dinosaurs were very specialized meat-eaters. Their arms were extremely short, and they had only two fingers (the thumb and the index finger). The arms of Gorgosaurus-like those of Tyrannosaurus- were so short they couldn't even reach its mouth! Tyrant dinosaurs' legs were long and slender, and their narrow, compact feet had a special shock-absorbing shape. A young Gorgosaurus was probably as fast as an ostrich dinosaur, and even an adult was probably faster than any of the duckbills and horned dinosaurs it hunted. Although its arms would be useless in catching prey, it could use its powerful jaws, filled with many strong teeth, to grab its victims. Tyrant dinosaurs' teeth, unlike those of most theropods, or meat-eating dinosaurs, were not shaped like blades. Instead, they were thick and round in cross-section. This meant that the teeth could be used to hold and grip tighter, and maybe even to crush bone. When tyrant dinosaurs were around, they were the largest predators in their environment. The only meat-eater a Gorgosaurus had to fear was another Gorgosaurus, or the even larger tyrant dinosaur Daspletosaurus, which lived at the same time. Of course, Gorgosaurus would have to be careful when attacking a Centrosaurus or other horned dinosaur. Although these ceratopsians ate plants, they could still defend themselves with their deadly horns.
Fun Facts[]
Gorgosaurus was once considered e species of Albertosaurus, which is really a different (but closely related) tyrant dinosaur from later in the Cretaceous.
Trivia[]
Almost every dinosaur labeled "Albertosaurus" in a museum is really a Gorgosaurus.
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