| Struthiomimus Temporal range: Late Cretaceous, 75–65.5 Ma |
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| Mounted S. sedens skeleton cast, Oxford University Museum of Natural History | |
| Scientific classification | |
| Phylum: | Chordata |
| Class: | Reptilia |
| Superorder: | Dinosauria |
| Order: | Saurischia |
| Suborder: | Theropoda |
| Family: | †Ornithomimidae |
| Genus: | †Struthiomimus Osborn, 1917 |
| Type species | |
| †Ornithomimus altus Lambe, 1902 |
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| Species | |
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†S. altus (Lambe, 1902 [originally Ornithomimus]) |
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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 4.3 metres (14 ft) long and 1.4 metres (4.6 ft) tall at the hips and weighed around 150 kilograms (330 lb).[1] Struthiomimus is one of the more common small dinosaurs in the Dinosaur 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.
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Struthiomimus had a typical build and skeletal structure for an ornithomimid, differing from genera like Ornithomimus and Dromiceiomimus in proportions and anatomical details.[3] It is known from several skeletons and skulls,[4] and its size is estimated as about 4.3 metres (14 ft) long and 1.4 metres (4.6 ft) tall at the hips, with a weight of around 150 kilograms (330 lb).[1] 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 were toothless. Its vertebral column had ten neck vertebrae, thirteen back vertebrae, six hip vertebrae, and about thirty-five tail vertebrae.[5] The tail was stiff and was probably used for balance.[6]
Struthiomimus had long slender arms and hands, with immobile forearm bones and limited opposability between the first finger and the other two.[7] It had the longest hands relative to the humerus of any ornithomimid, with particularly long claws.[4] The three fingers were roughly the same length, and the claws were only slightly curved; Henry Fairfield Osborn, describing a skeleton in 1917, compared the arm to that of a sloth.[6] Its shin was longer than its thigh, a cursorial feature.[6] Among ornithomimids, though, its legs were only moderately elongate.[1] Its feet were elongate, and the metatarsals were tightly appressed, with three toes tipped by claws with very slight curvature.[6]
Struthiomimus, being a member of Coelurosauria, probably had some kind of feathers, especially if the Therizinosauria and the Alvarezsauridae (of which at least one member, Shuvuuia is known to have been feathered) are closely related.
In 1901, Lawrence Lambe found some incomplete remains, holotype CMN 930, 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. Osborn complicated matters by assigning the better specimen, AMNH 5339, as the genoholotype.[6] Dale Russell made Struthiomimus a full genus in 1972, at the same time referring several other specimens to it: AMNH 5375, AMNH 5385, AMNH 5421, CMN 8897, CMN 8902 en ROM 1790, all partial skeletons.[8] In 1916 Osborn also renamed Ornithomimus tenuis Marsh 1890 into a Struthiomimus tenuis.[6] This is today considered a nomen dubium.
In subsequent years William Arthur Parks named four other species of Struthiomimus: Struthiomimus brevetertius Parks 1926,[9] Struthiomimus samueli Parks 1928,[10] Struthiomimus currellii Parks 1933 and Struthiomimus ingens Parks 1933.[11] These are today seen as either belonging to Dromiceiomimus or to Ornithomimus.
In 1997 Donald Glut mentioned the name Struthiomimus lonzeensis.[12] This was probably a lapsus calami, a mistake for Ornithomimus lonzeensis (Dollo 1903) Kuhn 1965.
Struthiomimus altus comes from the Late Campanian (Judithian age) Dinosaur Park Formation. A species of Struthiomimus is also known from the Late Campanian/Early Maastrichtian (Edmontonian age) Horseshoe Canyon Formation.[13] Because dinosaur fauna show rapid turnover, it is possible that these younger Struthiomimus specimens will prove to be a species distinct from S. altus, though no new name has been given to them. Struthiomimus specimens from the Hell Creek Formation are larger (similar to Gallimimus in size) and tend to have straighter and more elongate hand claws, similar to those seen in Ornithomimus. They most likely represent a separate species of Struthiomimus, in 2001 by James Orville Farlow named Struthiomimus sedens[14] (again, originally named as a species of Ornithomimus by Marsh, in 1892).[13][15]
In 2010 Gregory S. Paul renamed Ornithomimus edmontonicus Sternberg 1933 into a Struthiomimus edmontonicus,[16] but this has found no acceptance by other workers.
The cladogram presented here follows the one recovered by Turner, Clarke, Ericson and Norell, 2007.[17] Clade names follow definitions provided by Sereno, 2005.[18] |
Struthiomimus is a member of the family Ornithomimidae, a group which also includes Anserimimus, Archaeornithomimus, Dromiceiomimus, Gallimimus, Ornithomimus, and Sinornithomimus.
Just as the fossil remains of Struthiomimus were incorrectly assigned to Ornithomimus, the larger group that Struthiomimus belongs to, the Ornithomimosauria, also underwent many changes over the years. For example, O.C. Marsh initially 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 within Iguanodontia.[22] As late as 1993, Struthiomimus was referred to Oviraptorosauria.[23] However, by the 1990s, there were numerous studies that placed Struthiomimus within Coelurosauria.[24][25][26][27]
Recognizing the difference between ornithomimids and other theropods, Rinchen Barsbold placed ornithomimids within their own infraorder, Ornithomimosauria, in 1976.[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 was adopted by other authors at the beginning of the current century.
In a 2001 study conducted by Bruce Rothschild and other paleontologists, fifty foot bones referred to Struthiomimus were examined for signs of stress fracture, but none were found.[30]
There has been much discussion about the feeding habits of Struthiomimus. Because of its straight-edged beak, Struthiomimus may have been an omnivore. Some theories suggest that it may have been a shore-dweller and may have been a filter feeder.[5] Some paleontologists noted that it was more likely to be a carnivore because it is classified within the otherwise carnivorous theropod group.[31][8] This theory has never been discounted, but Osborn, who described and named the dinosaur, proposed that it probably ate buds and shoots from trees, shrubs and other plants,[3] using its forelimbs to grasp branches and its long neck to enable it accurately to select particular items. This herbivorous diet is further supported by the unusual structure of its hands. The second and third fingers were of equal length, could not function independently, 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 indicates that the hand was used as a "hook" or "clamp", for bringing branches or fern fronds at shoulder height within reach.[7]
The legs (hind limbs) of Struthiomimus were long, powerful and seemingly well-suited to rapid running, much like an ostrich. The supposed speed of Struthiomimus was, in fact, its main defense from predators (although it may also have been able to lash out with its hind claws when cornered), such as the dromaeosaurids (e.g. Saurornitholestes and Dromaeosaurus) and tyrannosaurs (e.g. Daspletosaurus and Gorgosaurus), which lived at the same time. It is estimated to have been able to run at speeds between 50 to 80 km/h (31 to 50 mph).[32]
Struthiomimus was one of the first theropods envisioned from the outset as having a horizontal posture. Osborn in 1916 let the animal intentionally be depicted with an elevated tail.[6] This newer view created an image much more reminiscent of modern flightless birds, such as the ostrich to which this dinosaur's name refers, but would only much later be accepted for all theropods.
The best-preserved skeleton of Struthiomimus is currently on display at the American Museum of Natural History, in Manhattan, New York, while the best-preserved skull is currently on display at the Royal Tyrrell Museum of Palaeontology, in Drumheller, Alberta, Canada.
Struthiomimus has appeared in several dinosaur-related films and television programs, such as the pair of bumbling egg-napping villains in The Land Before Time II: The Great Valley Adventure. They played a prominent role in the Disney animated film Dinosaur, and in 1985, Struthiomimus was featured in Dinosaur!, a CBS television documentary hosted by Christopher Reeve. In a stop-motion animation sequence, a Struthiomimus was shown feeding on hadrosaurid eggs and escaping the angry mother, only to be preyed upon by a pair of Deinonychus moments later (though in reality, Deinonychus lived in the early Cretaceous Period and was not a contemporary of Struthiomimus). Struthiomimus toys were included in the Dino-Riders line by Tyco and was later re-released in the Smithsonian toy line.