Coelurus fragilis (S/F)

Coelurus, meaning “hollow tail,” was a species of small theropod dinosaur in the family Coeluridae. The type species, and only known species at this time, is Coelurus fragilis; the species name refers to the fragile nature of the animal’s fossilized remains. It lived during the late Jurassic period, 155 to 152 million years ago, in what is now Wyoming.

This species of dinosaur was described in 1879 by Othniel Charles Marsh, its fossils having been found at Como Bluff within the Morrison Formation. The fossil consists of vertebrae, bones of the arms and legs, and possibly a lower jaw fragment from a second individual. In the initial description, Marsh was chiefly impressed by the hollow vertebrae, from which he gave the dinosaur its genus name. Because the remains were so fragmentary, Marsh was not certain at first whether the creature was a dinosaur or some other type of reptile, but it was confidently found to be dinosaurian when he returned to study it again in the early 1880s.

Like many dinosaurs found during the Bone Wars, Coelurus has a long and confusing taxonomic history, and for many years it was used as a wastebasket taxon for all new coelurosaurians which looked similar to it. Species of Coelurus throughout history have been widely reassigned to other genera, such as CoelophysisOrnitholestes, and Tanycolagreus. Today, there is only one known species of Coelurus.

At some point between 2005 and 2015, Coelurus was cloned by International Genetic Technologies operating under the banner of Masrani Global Corporation. The dinosaur was recreated using paleo-DNA recovered from Jurassic amber samples; it was intended for exhibition in the Jurassic World theme park, but there is currently no evidence that it was put on display. It is strongly suspected to have become extinct between late 2015 and 2017 due to neglect.


This was not a large dinosaur, reaching lengths of 7.9 feet (2.4 meters) and a height of 2.3 feet (70 centimeters) at the hips. Paleontologists estimate its weight to have been 29 to 44 pounds (13 to 20 kilograms). The vertebrae of Coleurus, in addition to being hollow like a modern bird’s, were longer than average; this gave the animal a lengthened torso and very long tail. Its tail in particular was about half of its overall length.

Coelurus also had a long neck. Fossils of its skull have yet to be discovered, but depictions of the animal (from the Jurassic World Facts application and associated action figure, currently the only known modern depictions of Jurassic‘s Coelurus) show it to have had a skull shape relatively similar to its relative Ornitholestes. The skull was perched atop the neck facing forward, with binocular vision and narrow jaws. Above its eyes were small, low triangular crests. According to the aforementioned application, the brain of Coelurus was twice as large as those of similarly-sized carnivorous animals.

The arms and legs of Coelurus were lanky. Its upper arm had a distinct S-shaped curve when viewed from the side and was slightly longer than the forearm, though in life the animal’s body may have obscured some of its upper arm length. Its thigh bones were S-shaped when viewed from the front, and its metatarsals were exceptionally long and slender. The hands and feet each had three digits ending in claws (each foot also had a fourth toe, a dewclaw, which was vestigial). According to the Jurassic World Facts application, Coelurus‘s long legs allowed it to reach some of the fastest speeds of any theropod; for comparison, Velociraptor antirrhopus can reach speeds of fifty to sixty miles per hour when at a sprint.

Later theropods would possess cloacae, which would house their reproductive organs. It is most likely that an earlier theropod such as Coelurus already possessed this structure.

While fossils have yet to show whether this animal had feathers in prehistory, its de-extinct clones created by InGen are not believed to have had any. Instead, its body was covered in scaly skin, with distinct raised scales on the back of the head and neck. It has been depicted as a brightly-colored animal, with a rosy red head; the color fades to pink on the neck and body, eventually becoming very pale and almost white on the tail. Its back has blue markings beginning just behind the eye orbits and extending to the hips. On the tail, this pattern changes to irregular stripes, ending almost at the halfway mark of the tail’s length. Its arms and lower legs are very pale pink, almost white, about the same color as the end of the tail. The underbelly is an off-white color as well, including the entire lower jaw.


No hatchlings or juveniles of Coelurus have yet been observed. Their growth patterns are unknown.

Sexual Dimorphism

There is currently no known sexual dimorphism in Coelurus. The animal depicted in the Jurassic World Facts application is said to be a female, and is the only known depiction of this creature in the franchise’s present day.

Preferred Habitat

Fossil evidence suggests that the Coelurus lived in semi-arid environments and was evolved to survive through wet and dry seasons. It inhabited floodplains, conifer forests, and savannas. In the modern day, it was able so survive in tropical environments with human assistance.

Isla Nublar

Sometime between 2005 and 2015, Coelurus was hatched on Isla Nublar with the intent to eventually exhibit it in the Jurassic World theme park. There is currently no evidence that any ever made it to display. They were likely housed in habitats in Sector 5, in the northern region of the island, though their population statistics for this time are unknown.

After the 2015 incident closed Jurassic World permanently, Coelurus and the other dinosaurs were able to roam the island and were left at the mercy of nature and each other. A report by the Dinosaur Protection Group released on February 4, 2018 heavily implies that Coelurus became extinct at some point before that date. No surviving populations have been confirmed.

Isla Sorna

There is no evidence that Coelurus was ever introduced to Isla Sorna.


Isla Nublar and the Muertes Archipelago were subject to dinosaur poaching attempts throughout the 2000s and 2010s. It is currently unknown what species may have been illegally removed from the island, or where (aside from mainland Central America) they may have been taken. Coelurus, with its manageable size, could have easily been smuggled onto even smaller boats or aircraft. Unfortunately, there is no evidence that any are still living.

Behavior and Ecology
Daily Activity

The activity patterns of Coelurus are presently unknown.

Diet and Feeding Behavior

Coelurus was a carnivore, feeding on smaller animals than itself. Its long arms and legs would have helped it to grapple with prey such as insects and small vertebrates, though it was likely not strong enough to threaten animals much larger than itself.

Social Behavior

If the bright colors of the Mattel Coelurus are taken as film canon, then Coelurus is most likely a social animal that uses visual displays.


All dinosaurs lay eggs to reproduce. Theropod eggs, like those of Coelurus, are typically ovoid in shape to prevent them from rolling. A small dinosaur like Coelurus would have an incubation period lasting around three to six months, though the actual incubation time is unknown due to a lack of observations.


Any vocalizations used by Coelurus are currently unknown. If it is brightly-colored as has been depicted, then it most likely used forms of visual signalling.

Ecological Interactions

There is a lack of data on Coelurus ecology, but it is believed to have been a terrestrial hunter and fairly low on the food chain. Certainly, after being released into the wild of Isla Nublar, it would have been possible prey for a multitude of carnivorous de-extinct animals, which likely contributed to its decline on the island.

This animal likely fed on Isla Nublar’s smallest wildlife: lizards, frogs, rats, insects, and birds. It may have preyed upon the smallest of dinosaurs, including Compsognathus, Microceratus, and Segisaurus, while itself being prey to the larger theropods and other carnivores.

Relationship to Humans

Little is known about how Coelurus interacted with humans since being cloned. It was not a very large carnivore, and had a fragile lightweight build. This likely made it mostly non-threatening, and it would have been easier to handle than most of InGen’s theropods. However, it was extremely speedy, making it potentially difficult to recapture if it escaped.

It was planned to be exhibited in the Jurassic World theme park, but as of late 2015, there is no evidence that any were ever integrated to the park. With Jurassic World’s closure in December of that year, Coelurus was abandoned to its fate, and is now probably extinct.

Behind the Scenes

Coelurus was first introduced to the Jurassic Park franchise via Michael Crichton‘s original novel. It was named as being a species that was currently in the works, having yet to be produced. It was introduced to S/F canon through viral marketing with the Dinosaur Protection Group, which led to a toy being produced by Mattel for the Jurassic World: Fallen Kingdom line.