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Struthiomimus

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Struthiomimus (meaning "ostrich mimic", from the Greek στρούθειος/stroutheios meaning "of the ostrich" and μῖμος/mimos meaning "mimic" or "imitator") is a genus of ornithomimid dinosaur from the late Cretaceous of Alberta, Canada. It was a long-legged, ostrich-like dinosaur.

The bipedal Struthiomimus stood about 14 ft long and 4.6 ft tall at the hips and weighed around 330 pounds.[1] Struthiomimus is one of the more common small dinosaurs in the Provincial Park; its abundance suggests that it was a herbivore or omnivore rather than a carnivore. [2]

Like many other dinosaur genera discovered in the 19th century, the history of Struthiomimus is convoluted. The first known fossils of Struthiomimus were named Ornithomimus sedens by Othniel Charles Marsh in 1892, and a subsequent species was named O. altus by Lawrence Lambe in 1902. It wasn't until 1917 that Henry Fairfield Osborn named Struthiomimus from fossils discovered in 1914 from the Red Deer River site in Alberta.

Description

Struthiomimus had a typical build and skeletal structure for an ornithomimid, differing from genera like Ornithomimus and Dromiceiomimus in size and anatomical details.[3] It is known from some skeletons and skulls,[4] and its size is about 14 ft long and 4.6 ft tall at the hips, with a weight of around 330 pounds. [5] As with other ornithomimids, it had a small slender head on a long neck (which made up about 40% of the length of the body in front of the hips).[4] Its eyes were large and its jaws had no teeth. Its spine had 10 neck vertebrae, 13 back vertebrae, 6 hip vertebrae, and about 35 tail vertebrae.[6] The tail was stiff and was likely used for balance.[7]

Struthiomimus had long arms and hands, with still forearm bones and limited opposability between the first finger and the other two.[8] It had the longest hands of any ornithomimid, with particularly long claws.[4] The three fingers were roughly the same length, and the claws had a slight curve; Henry Fairfield Osborn, describing a skeleton in 1917, said the arm was like that of a sloth.[7] Its shin was longer than its thigh, a feature for running.[7] Among ornithomimids, though, its legs were of moderate length. [9] Its feet were long, with three toes tipped by claws with a slight curve.[7]

Struthiomimus, being a coelurosaur, probably had some kind of feathers.

History

In 1901, Lawrence Lambe found some incomplete remains, and named them Ornithomimus altus, placing them in the same genus as material earlier described by Othniel Charles Marsh in 1890. The specific name altus is from Latin, meaning "lofty" or "noble". However, in 1914, a nearly complete skeleton was discovered by Barnum Brown at the Red Deer River site in Alberta, and officially described as the subgenus Struthiomimus by Henry Fairfield Osborn in 1917.[10]

In years to come William Arthur Parks named four more species of Struthiomimus: Struthiomimus brevetertius Parks 1926,[11] Struthiomimus samueli Parks 1928,[12] Struthiomimus currellii Parks 1933 and Struthiomimus ingens Parks 1933.[13] These are now thought to either come from to Dromiceiomimus or to Ornithomimus.

In 1997 Donald Glut mentioned the name Struthiomimus lonzeensis.[14] This was probably a mistake for Ornithomimus lonzeensis{C (Dollo 1903) Kuhn 1965. {C Struthiomimus altus comes from the Dinosaur Park Formation and a species of Struthiomimus is known from the Horseshoe Canyon Formation.[15] Since dinosaur fauna show rapid turnover, it could be that these younger Struthiomimus specimens will prove to be a species distinct from S. altus, though they have no new name. Struthiomimus specimens from the Hell Creek Formation are larger (similar to Gallimimus in size) and tend to have straighter and longer hand claws, like those seen in Ornithomimus. They most likely represent a separate species of Struthiomimus, in 2001 by James Orville Farlow named Struthiomimus sedens[16] (again, first named as a species of Ornithomimus by Marsh, in 1892).[15][17]

In 2010 Gregory S. Paul renamed Ornithomimus edmontonicus Sternberg 1933 to a Struthiomimus edmontonicus,[18] but this has found no acceptance by other workers.

Classification

Struthiomimus is a member of the family Ornithomimidae, a group which also includes Anserimimus, Archaeornithomimus, Dromiceiomimus, Gallimimus, Ornithomimus, and Sinornithomimus.

Just as the bones of Struthiomimus were wrongly assigned to Ornithomimus, the larger group that Struthiomimus belongs to, the Ornithomimosauria, also went thorugh many changes over the years. For example, O.C. Marsh at first included Struthiomimus in the Ornithopoda, a large clade of dinosaurs not closely related to theropods. [19] Five years later, Marsh classified Struthiomimus in the Ceratosauria. [20] [21] In 1891, Baur placed the genus in Iguanodontia.[22] As late as 1993, Struthiomimus was referred to Oviraptorosauria.[23] However, by the 1990s, there were a lot of studies that placed Struthiomimus in Coelurosauria.[24][25][26][27]

In 1976, Rinchen Barsbold saw the difference between ornithomimids and other theropods, and placed ornithomimids in their own infraorder, Ornithomimosauria.[28] The constituency of Ornithomimidae and Ornithomimosauria varied with different authors. Paul Sereno, for example, used Ornithomimidae to include all ornithomimosaurians in 1998, but subsequently changed to a more exclusive definition (advanced ornithomimosaurs) within Ornithomimosauria,[29] a classification scheme that other authors took up at the beginning of the current century.

Paleobiology

Diet

There has been much talk of what Struthiomimus ate. Its straight-edged beak shows that Struthiomimus may have been an omnivore. Some theories suggest that it may have shore-dweller and may have been a filter feeder. [30] Some paleontologists note that it was more likely that it ate meat as it is classified in the otherwise meat-eating theropod group. [31] [32]This theory has not been discounted, but Osborn, who described and named the dinosaur, proposed that it probably ate buds and shoots from trees, shrubs and other plants, [33]using its front limbs to grasp branches and its long neck to let it take particular things. This plant-based diet is backed up by the strange structure of its hands. The second and third fingers were of the same length, could not work on their own, and were probably bound together by skin as a single unit. The structure of the shoulder girdle did not allow a high elevation of the arm nor was optimised for a low reach. The hand could not be fully flexed for a grasping motion or spread for raking. This is a sign that the hand was used as a "hook" or "clamp", to bring branches or fern fronds at shoulder height within reach. [34]

Speed

The legs (hind limbs) of Struthiomimus were long, strong, and seemed to be well-suited to run fast, much like an ostrich. The supposed speed of Struthiomimus was, in fact, its main defense from predators (though it may also have been able to lash out with its hind claws when trapped), such as the dromaeosaurids (e.g. Saurornitholestes and Dromaeosaurus) and tyrannosaurs (e.g. Daspletosaurus and Gorgosaurus), which lived at the same time. It is thought to have been able to run at speeds from 31 to 50 mph. [35]

Posture

Struthiomimus was one of the first theropods pictured from the start with a horizontal posture. Osborn in 1916 let the animal intentionally be drawn with a raised tail. [36]This newer view created an image much more similar to modern flightless birds, such as the ostrich to which this dinosaur's name comes from, but would only much later be accepted for all theropods.

References

Template:References

External links


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