Utahraptor

***Utahraptor*** (meaning "Utah's thief") is a genus of large dromaeosaurid dinosaur that lived in North America during the Early Cretaceous period. It was a heavy-built, ground-dwelling, bipedal carnivore. It contains a single species, ***Utahraptor ostrommaysi***, which is the largest-known member of the family Dromaeosauridae.

## Description

The holotype of *Utahraptor*, CEU 184v.86 consists of a second pedal ungual, with potentially assigned elements from other specimens: pedal ungual CEU 184v.294, tibia CEU 184v.260 and premaxilla CEU 184v.400. These elements have huge proportions compared to other dromaeosaurids, suggesting an animal about twice the length of *Deinonychus* or, surpassing it in a 100%. Like other dromaeosaurids, *Utahraptor* had large curved claws on their second toes. The second pedal ungual is preserved at 22 cm (8.7 in) in length and is estimated to reach 24 cm (9.4 in) restored.

The largest described *U. ostrommaysi* specimen (BYUVP 15465, referred by Erickson *et al.* 2009) is estimated to have reached up to 7 m (23 ft) long and somewhat less than 500 kg (1,100 lb) in weight, comparable to a polar bear in weight. In 2012, the paleontologist Thomas R. Holtz Jr. estimated its weight around 230 to 450 kg (500 to 1,000 lb), comparable to a grizzly bear. However, the 2001 Kirkland discovery indicates the species may be far heavier than previously estimated. In 2016 Rubén Molina-Pérez and Asier Larramendi estimated the largest specimen (BYU 15465) at 4.65 m (15.3 ft) long, 1.5 m (4.9 ft) tall at the hips and 280 kg (620 lb) in weight; they claim the larger estimates are due to nine specimens of various ages being mixed.

For instance, some elements were wrongly referred to the genus; the lacrimal bone of the specimen CEU 184v.83 turned out to be a postorbital from the ankylosaur *Gastonia*. Britt *et al.* also suggested that the previously identified manual unguals of the specimens CEU 184v.294, BYU 9438 and BYU 13068 are indeed pedal unguals. This suggestion was confirmed by Senter in 2007.

According to Kirkland *et al.* in 1993, *Utahraptor* can be recognized by the following autapomorphies: claws on the hand that are more specialized as cutting blades than in other dromaeosaurids; a lacrimal bone with distinctly parallel mesial and outer sides, giving it an elongate subrectangular appearance in top view, and a base of nasal opening on the premaxilla parallel to the premaxillary tooth row. In the revised diagnosis conducted by Turner *et al.* in 2012, *Utahraptor* differs from other dromaeosaurids in: an elongate nasal process of the premaxilla; a distal end of metatarsal III that is smooth, not ginglymoid; an L-shaped quadratojugal without a posterior process; the presence of a well-developed notch between the lesser trochanter and greater trochanter; and dorsal vertebrae that lack pleurocoels.

Although feathers have never been found in association with *Utahraptor* specimens, there is strong phylogenetic evidence suggesting that all dromaeosaurids possessed them. The genus *Microraptor* is one of the oldest-known dromaeosaurids, and is phylo­genetically more primitive than *Utahraptor*. Since *Microraptor* and other dromaeosaurids possessed feathers, it is reasonable to assume that this trait was present in all of Dromaeosauridae. Feathers were very unlikely to have evolved more than once, so assuming that any given dromaeosaurid, such as *Utahraptor*, lacked feathers would require positive evidence that they did not have them. So far, there is nothing to suggest that feathers were lost in larger, more derived species of dromaeosaurs. The presence of quill knobs in *Dakotaraptor* evidenced that even larger dromaeosaurids had feathers.

## *Utahraptor* in The Amazing Dinosaur Adventure

A stampede of *Utahraptor* from *The Lonely Journey*