page_title: Coelurus
section_title: History
hierarchical_section_title: Coelurus / History
caption_attribution_description: Vertebrae of Coelurus
context_page_description: Coelurus is a genus of coelurosaurian dinosaur from the Late Jurassic period. The name means "hollow tail", referring to its hollow tail vertebrae. Although its name is linked to one of the main divisions of theropods, it has historically been poorly understood, and sometimes confused with its better-known contemporary Ornitholestes. Like many dinosaurs studied in the early years of paleontology, it has had a confusing taxonomic history, with several species being named and later transferred to other genera or abandoned. Only one species is currently recognized as valid: the type species, C. fragilis, described by Othniel Charles Marsh in 1879. It is known from one partial skeleton found in the Morrison Formation of Wyoming, United States. It was a small bipedal carnivore with elongate legs.
context_section_description: Coelurus was described in 1879 by Othniel Charles Marsh, an American paleontologist and naturalist known for his "Bone Wars" with Edward Drinker Cope. At the time, he only described what he interpreted as vertebrae from the back and tail, found at the same location as the type specimen of his new genus and species Camptonotus dispar (later renamed Camptosaurus because Camptonotus was already in use for a cricket). Marsh was impressed with the hollow interiors of the thin-walled vertebrae, a characteristic that gave the type species its name: Coelurus fragilis. He thought of his new genus as an "animal about as large as a wolf, and probably carnivorous". Coelurus would prove to be the first named small theropod from the Morrison Formation, although at the time Marsh was not certain that it was a dinosaur. He returned to it in 1881 and provided illustrations of some bones, along with putting it in a new order (Coeluria) and family (Coeluridae).
  From there, the story becomes more complex. Apparently, the skeleton was scattered throughout the quarry, with the remains being recovered from September 1879 to September 1880. Marsh elected to place some of the material in a new species, C. agilis, on the strength of a pair of fused pubic bones he thought belonged to an animal three times the size of C. fragilis. He returned to the genus in 1888 to add C". gracilis, based on unknown remains only represented today by a single claw bone pertaining to a small theropod from the Early Cretaceous Arundel Formation of Maryland. This species is not currently accepted as representing Coelurus in reviews of the genus, but has not been given its own genus.
  Despite their professional animosity, Cope also assigned species to Coelurus; in 1887, he named fossils from the Late Triassic of New Mexico as C. bauri and C. longicollis. He later gave them their own genus, Coelophysis.
  In 1903, Henry Fairfield Osborn named a second genus of small theropod from the Morrison Formation, Ornitholestes. This genus was based on a partial skeleton from Bone Cabin Quarry, north of Como Bluff. Ornitholestes became intertwined with Coelurus in 1920, when Charles Gilmore, in his influential study of theropod dinosaurs, concluded that the two were synonyms. This was followed in the literature for decades. The two genera were not formally compared, however, nor was there a full accounting of what actually belonged to Coelurus, until John Ostrom's study in 1980.
  Gilmore had suspected that C. fragilis and C. agilis were the same, but Ostrom was able to demonstrate this synonymy. This greatly expanded the known material pertaining to C. fragilis, and Ostrom was able to demonstrate that Ornitholestes was quite different from Coelurus. At the time, Dale Russell had proposed that C. agilis was a species of Elaphrosaurus based on the incomplete information then published; Ostrom was also able to demonstrate that this was not the case. Additionally, he showed that one of the three vertebrae Marsh had illustrated for C. fragilis was actually a composite of two vertebrae, one of which was later shown to come from another quarry and belonged not to Coelurus but to another, unnamed small theropod. This unnamed genus would not be the last small theropod from the Morrison Formation to be confused with Coelurus; a later discovery (1995) of a partial skeleton in Wyoming was first thought to be a new larger specimen of Coelurus, but further study showed it belonged to a different but related genus, Tanycolagreus.
caption: Othniel Charles Marsh's illustration of Coelurus vertebrae from 1884
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