Ornitholestes

*Ornitholestes hermanni*

* Jurassic Park Institute Artwork
* Robert F Walters Artwork

***Ornitholestes*** (meaning "bird robber") was a small theropod dinosaur of the late Jurassic of Western Laurasia (the area that was to become North America). To date, it is known only from a single partial skeleton, and badly crushed skull found at the Bone Cabin Quarry near Medicine Bow, Wyoming, in 1900. It was described by Henry Fairfield Osborn in 1903. An incomplete hand was later attributed to *Ornitholestes*, although it now appears to belong to *Tanycolagreus*. The type (and only known) species is *O. hermanni*. The species name honors the American Museum of Natural History preparator Adam Hermann.

## Description

*Ornitholestes* was a bipedal carnivore. Its head was proportionally smaller than that of most other predatory dinosaurs, but the skull was heavily built, with a short snout and robust lower jaw. The orbits (eye sockets) were quite large, measuring over 25 percent of the skull's length. There is no indication of a bony eye ring.

The front teeth of *Ornitholestes* were somewhat conical, with reduced serrations; the back teeth were recurved and more sharply serrated, similar to those of other theropod dinosaurs. Henry Fairfield Osborn (1903) counted four teeth in the premaxillae, of which the front tooth was the largest in the upper jaw. In contrast, Gregory S. Paul (1988) depicted the skull with only three premaxillary teeth remaining, much smaller than those illustrated by Osborn. Each maxilla (main tooth-bearing bone in the upper jaw) contained ten teeth, and each dentary (tooth-bearing bone in the lower jaw) contained twelve teeth. The tooth rows of *Ornitholestes* were short, with the dentary (lower) row being even shorter than the maxillary (upper) row,[10] even though the dentary bone itself was exceptionally long at the back, reaching a point below the middle of the eye socket. Teeth did not extend as far back as the orbits, and neither tooth row spanned much more than one-third of the skull.

An area of broken bone near the external naris (nostril) appears to bulge upward, which led Gregory S. Paul to suggest in Predatory Dinosaurs of the World (1988) that *Ornitholestes* had a nasal horn "rather like a chicken's comb in looks." Both Oliver W.M. Rauhut (2003) and Kenneth Carpenter et al. (2005a) rejected that interpretation, and indicated that the upward flare of bone was due to post-mortem crushing of the skull. Paul's updated illustration of *Ornitholestes* in his 2010 Princeton Field Guide to Dinosaurs no longer contains the nasal horn.

*Ornitholestes* had a relatively short neck with a slight sigmoidal (S-shaped) curve. The tail was long and whiplike, comprising over half of the body's length. Not all of the vertebrae were preserved, but Osborn (1917) estimated that *Ornitholestes* had nine or ten cervical (neck) vertebrae, thirteen dorsal (back) vertebrae, four sacral (hip) vertebrae, and 39 to 44 caudal (tail) vertebrae. Carpenter et al. (2005a) recorded that the specimen contained five sacral vertebrae. *Ornitholestes* was a short-bodied theropod, and this was reflected in the short front-to-back dimensions of the cervical and dorsal vertebrae.

The forelimbs of *Ornitholestes* were relatively long, slightly under two-thirds the length of the hind legs. The humerus (upper arm bone) was heavily built, and somewhat longer than the radius and ulna (forearm bones). Both the humerus and radius were straight-shafted. The claws on digits I and II of the hand were about the same size. Although the hand's third ungual (claw bone) was not preserved, extrapolation from the closest relatives of *Ornitholestes* indicates that it was probably shorter than the first two.

*Ornitholestes* is often portrayed as a fast, long-legged theropod, but its lower limb bones were fairly short. Osborn (1917) calculated that the, missing, tibia (shin bone) was only about 70.6% as long as the femur (thigh bone). The metatarsals (foot bones) were spaced closely, but not fused together. As is typical of theropods, the feet were tridactyl (with three clawed weight-bearing toes). John H. Ostrom (1969) noted that the claw of digit II (the innermost toe) was larger than those of digits III and IV, and suggested that this digit may have borne a modified sickle claw similar to that of *Deinonychus*. However, as both Ostrom (1969) and Paul (1988) noted, the poor preservation of digit II makes this hypothesis difficult to confirm.

In his 1903 description, Osborn wrote that the length of *Ornitholestes* along "the skull and vertebral column as restored" was 2.22 m (7.28 ft). However, this reconstruction was inaccurate, being based in part on Othniel Charles Marsh's restoration of the basal sauropodomorph *Anchisaurus*, and the neck and trunk were both too elongated. David Norman (1985) and John Foster (2007) both estimated that Ornitholestes was about 2 m (6.6 ft) long. Gregory S. Paul's 1988 Predatory Dinosaurs of the World listed the length of *Ornitholestes* as approximately 2.08 m (6.82 ft).

Paul (1988) and Foster (2007) both estimated that *Ornitholestes* weighed 12.6 kg (27.8 lb). John A. Long and Peter Schouten (2008) suggested a slightly higher figure, 15 kg (33 lb).

## Discovery and naming

Ornitholestes was the first theropod to be discovered in the 1900s. The holotype skeleton (AMNH 619) was excavated in July 1900 in the Bone Cabin Quarry in Wyoming by an American Museum of Natural History expedition by Peter C. Kaisen, Paul Miller and Frederic Brewster Loomis. It represents a partial skeleton with skull, including numerous elements of the vertebral column, the forelimbs, pelvis and hindlimbs. Henry Fairfield Osborn named and scientifically described the specimen in 1903. The genus name Ornitholestes, initially suggested by Theodore Gill, means "bird robber" and is derived from the Greek ὄρνις/ornis, ornithos ("bird") and λῃστής/lestes ("robber"). The species name (O. hermanni) honors Adam Hermann, the head preparator at the Museum, who directed the restoration and mounting of the skeleton.

An incomplete hand (AMNH 587) was assigned to *Ornitholestes* by Osborn in his 1903 description of the genus. However, as Gregory S. Paul (1988) noted, the poor preservation of the corresponding elements in the type specimen made this association "tentative." In 2005, Kenneth Carpenter et al. described a new small theropod, *Tanycolagreus*, whose skeleton was found in Bone Cabin Quarry only a few hundred yards from AMNH 587. Since AMNH 587 was virtually identical to the preserved hand of the *Tanycolagreus* type specimen, it is now considered to belong to that dinosaur and not to *Ornitholestes*. Following this reassignment, Phil Senter (2006) noted that "our knowledge of *Ornitholestes* can be drawn now only from the holotype."[45] John Foster (2007) reported that some fragments from Dry Mesa Quarry may belong to *Ornitholestes*, though these have not yet been described.

In 1920 Charles Whitney Gilmore concluded that *Ornitholestes* was identical to *Coelurus*; in 1934 Oliver Perry Hay recognised only a difference at the species level, naming a *Coelurus hermanni*,[48] but in 1980 John Ostrom revived the genus.

## General description

A crew from the American Museum of Natural History found the first remains of *Ornitholestes* (or "bird robber") at Bone Cabin Quarry near Medicine Bow, Wyoming, in 1900. It is consisted of a skull and partial skeleton. This is the same quarry where workers found *Apatosaurus*, now mounted in the American Museum of Natural History.

H.F. Osborn briefly described *Ornitholestes* in 1903. In that paper, he also grouped a partial hand from the same quarry, but not the same animal, in the same genus. The skull is complete, though badly crushed. Serrated teeth line the jaws. The first tooth in the upper jaw is the largest. *Ornitholestes* may have had a small horn over its nose, but scientists are not sure.

The hands are not complete. If the partial hand of the other animal belongs to the same genus, the first finger was short, and the second and third fingers were much longer. *Ornitholestes* may have caputered and held its prey with its hand. All the fingers had sharp curved claws. The animal probably weighed about 35 pounds. For many years, scientists thought *Ornitholestes* and *Coelurus* were the same genus. In 1980, however, John Ostrom showed that they weren't. It lived alongside dinosaurs like *Stegosaurus*, *Diplodocus*, *Dryosaurus*, *Ceratosaurus*, and *Allosaurus*, and also pterosaurs like Rhamphorhynchus.

Height. 3 feet

Length. 7 feet

## Classification

The infraorder Coelurosauria, coined in 1914 by Friedrich von Huene, was traditionally a taxonomic wastebasket into which all small theropods were placed. Ornitholestes, due to its small size, was therefore generally classified as a coelurosaur. In 1986, Jacques Gauthier redefined this and several other paleontological terms in a more rigorous fashion, based on cladistic methods. Tetanurae was defined as modern birds and all theropods more closely related to modern birds than to ceratosaurs, while Coelurosauria now comprised all members of Tetanurae more closely related to modern birds than to carnosaurs. In 1988, Gregory S. Paul suggested that Ornitholestes was very similar in skull structure to Proceratosaurus, a Middle Jurassic theropod from England. He placed these two genera together in Ornitholestinae—a new subfamily under Allosauridae—and speculated that they were more closely related to the much larger Allosaurus than to other small theropods. However, the classification of Ornitholestes and Proceratosaurus as allosaur relatives proved untenable (the latter has since proved to be a tyrannosauroid), and Paul eventually abandoned it. All published cladistic analyses have shown Ornitholestes to be a coelurosaur as defined by Gauthier. Some analysis have shown support for the hypothesis that it is the most primitive member of the group Maniraptora, though more thorough analyses have suggested it is more primitive than the Maniraptoriformes, and possibly a close relative of the "compsognathid" Juravenator.

## JPInstitute.com Description

Ornitholestes was a smaller dinosaur that we know very little about. Only one skeleton has ever been found and it is missing a few parts. It got its name kind of by accident because the scientist who found it put the wrong hands on it at first (it was found mixed in with other dinosaur bones). He thought the hands could catch birds, so he called it a Bird Robber.

The skull of this dinosaur was crushed flat when it was discovered and some of the bone near the tip is missing. A few of the scientists who have studied the specimen believe that it may have had a small, flat horn on the end of its snout. But as this can't be determined for certain without another specimen, that is just a guess.

## Dinosaur Field Guide Description

Oritholestes (bird thief") is the best-known small theropod, or meat-eating dinosaur, from the famous Morrison Formation. The formation is a series of rocks in the western United States in which the best Late Jurassic dinosaur fossils in the world are found. The Morrison is well known for its sauropods (giant long-necked dinosaurs), impressive stegosaurs (plated dinosaurs), and giant meat-eaters such as Allosaurus and Ceratosaurus. However, small predators are also found in these rocks. Ornitholestes is a small dinosaur, about 6.9 feet (2.1 m) long, half of which is tail. It has long arms some paleontologists suggest that it could use these arms to catch birds. There is no evience of this behavior, but primitive birds would have been about the proper size for this dinosaur to eat. More common victims may have been mammals, lizards, and baby dinosaurs. The only known skull of Ornitholestes is damaged near the tip of its snout. It may have had a small horn over its nose.

### Fun Facts

A famous painting by Charles R Knight showed an Ornitholestes leaping after an Archaeopteryx Ornitholestes may have eaten early birds, but Archaeopteryx itself lived in a different part of the world, and it is unlikely that even an agile hunter like Ornitholestes could have caught a bird in midair.

### Trivia

Ornitholestes is not the only small theropod from the Morrison Formation; another such dinosaur is called Coelurus.

## Appearance in other media

### *Jurassic Park*

* It appears in *The Lost World* novel. Campers find the corpse of a large reptile on the beach of Rojas. Martin "Marty" Guitierrez invites Richard Levine to identify the creature. The corpse is destroyed by soldiers shortly after the scientists arrive. Levine identifies the creature as an *Ornitholestes*. Levine manages to save a skin sample from the creature. The sample is send to Ian Malcolm. Elizabeth Gelman analyzes the sample and shows the results to Malcolm. The skin has a structure comparable with pelicans; although it doesn't have feathers. It also has a 2 cm square green plastic radio tag. Elizabeth Gelman also notes that the skin contains a density of chromatophores, or pigment-bearing cells. The chromatophore could open and close. Meaning that this animal could change color, like a chameleon.

## Links

http://web.archive.org/web/20030221120550fw\_/http://www.jpinstitute.com/dinopedia/dinocards/dc\_ornith.html#

## References

1. ↑ 1.0 1.1 "Ornitholestes." In: Dodson, Peter & Britt, Brooks & Carpenter, Kenneth & Forster, Catherine A. & Gillette, David D. & Norell, Mark A. & Olshevsky, George & Parrish, J. Michael & Weishampel, David B. *The Age of Dinosaurs*. Publications International, LTD. p. 76. ISBN 0-7853-0443-6.
2. ↑ Template:Cite journal
3. ↑ Template:Cite book