Utahraptor

Credit: Fred Wierum.

*Utahraptor* is a genus of large dromaeosaurid dinosaur that lived in Utah during the Early Cretaceous.

## History

Jim Jenson (1975) discovered the first *Utahraptor* remains at Dalton Wells quarry and James "Jim" Kirkland, Robert Gaston, and Donald Burge (1993) named *U. ostrommaysi*. The original discovery did not get much attention,Carl Limone (October 1991) discovered a large foot claw brought attention to this new taxon. The naming team (1991) discovered the additional specimens at Gaston Quarry at the Yellow Cat and Poison Strip members of the Cedar Mountain Formation. CEU 184v86 (at the College of Eastern Utah Prehistoric Museum) is the holotype. The largest collection of specimens is deposited at the Brigham Young University[*citation needed*]. The name means "Utah thief" and the specific epithet is after John Ostrom, who studied *Deinonychus* and it's avian relations, and Chris Mays, who funded the research by founding Dinamation. It was earlier intended to be named "U. spielbergi" after Steven Speilberg who had directed Jurassic Park (1993) (which starred *Velociraptors* similar to *Utahraptor*) in exchange for research funding. However, this deal fell through, as no decision could be reached as to how much funding would be granted. Tjiago Vernaschi V. Costa and David Normand (2019) criticized the specific epithet *U. "ostrommaysorum"*, since it lacks justification. It had been widely used by many authors despite the naming paper using *"U. ostrommaysi"*, and the ICZN does not provide genitive epithets formed by two persons with different names. They suggest *"U. ostrommaysorum"* should be disused in favour of the old spelling and the new spelling be regarded as a random combination of letters rather than genitive. "*Ostromaysi*", "*ostromaysorum*", "*ostromayssorum*", "*ostromayorum*" and "*ostrommaysori*" are other common lapsus.

## Description

*Utahraptor* is so popular that the Utah state dinosaur, *Allosaurus*, was going to be replaced by *Utahraptor*. Instead, *Utahraptor* was also given the title alongside *Allosaurus*. *Utahraptor* is one of the biggest dromaeosaurs alongside rather vague or even dubious *Dakotaraptor* and *Deinonychus*. BYUVP 15465 was referred by Erickson et al. 2009, being up to 7 meters long and less than 500 kilograms heavy, making it the largest known individual. Thomas R. Holtz Jr. (2012) estimated a weight og 230-450 kilograms. However, Kirkland (2001) indicates a much heavier weight. Rubén Molina-Pérez and Asier Larramendi (2016) estimate BYU 15465 as 4.65 meters long, 1.5 meters at the hips and 280 kilograms heavy. The larger estimates are based on a mixed hypodigm of many individuals with various ages. Kirkland et al. (1993) state that *Utahraptor* is distinguished through more specialized cutting claws on the hand, a lacrimal with parallel mesial and outer sides and the base of the nasal opening is parallel on the premaxilla to the premaxillary tooth row. *Utahraptor* is found in association with feathers and phylogenetic evidence supports feathers in dromaeosaurs, so there is no direct evidence that *Utahraptor* and other large forms lacked feathers.

## Paleobiology

### Hunting

Kirkland et al. note that, given how large it was, it would not have been as fast as *Deinonychus* or *Velociraptor*. Instead they assume a speed similar to contemporary iguanodonts and faster than sauropods. A thick tibia indicates a large leg force that could kill prey. It may have kicked forward with its legs, but was likely so heavy that it did not to use its arms as balance (like smaller forms would have needed to). This would have freed the hands for other uses, such as dispatching prey. G.S. Paul states that Utahraptor was not very fast and was likely adapted to ambush, preying on iguanodonts and therizinosaurs. It's large sickle claw was suited to hunting large prey. It likely relied on it's jaws while hunting, more so than other dromaeosaurids. Bruce Rothschild (2001) examined for stress fractures in referred specimens, finding none. This indicates an unexpected condition or behaviour. *Utahraptor* was important as a major predator and could attack much larger prey. If a pack consisting of 3.5 meter long and 70 kilograms heavy individuals existed, they could take on prey 8 meters long and 1-2 tonnes heavt. Sauropods about 20 meters long may have been a key element to their diets, if it was social.

### Social Behavior

Kirkland et al. (2001) investigated a graduate student's discovery of a bone protruding from a 9-ton block of sandstone. It contained at least 7 individuals, including one 4.8 meters long, 4 juveniles and a hatchline 1 meter long. 1 possible iguanodont is also with this group. They speculate that the pack attempted to scavenge carrion or attack the iguanodont in quicksand, and themselves were instead captured. This may be one of the best-preserved predator traps discovered, and may have information on Utahraptor behaviour (such as pack hunting), but it is uncertain if they were mired all at once or one-by-one, Further examination suggests the amount of remains entrapped in the block may be 2x what was originally presumed. A 2020 study suggests *Deinonychus* did not have complex pack structure like modern animals and did not live in life-long family groups. It is unknown if this carried over to *Utahraptor*. However, many other animals such as squid, whales, some predatory fish, crocodilians and varanids do not live in life-long family groups but are still pack hunters, which the study ignored .

## Synonyms

* *U. ostromaysi* (lapsus)
* *U. ostromaysorum* (lapsus)
* *U. ostromayssorum* (lapsus)
* *U. ostromayorum* (lapsus)
* *U. ostrommaysori* (lapsus)
* *U. ostrommaysorum* (lapsus)
* "U. spielbergi"

## References

1. ↑ https://youtu.be/Thhb6Jy-Acw?t=801
2. ↑ https://nhmu.utah.edu/utahraptor-ostrommaysorum
3. ↑ https://en.wikipedia.org/wiki/Utahraptor
4. ↑ https://www.smithsonianmag.com/science-nature/utahraptor-largest-raptor-180974954/
5. ↑ 5.0 5.1 5.2 https://www.academia.edu/225747
6. ↑ https://ui.adsabs.harvard.edu/abs/2016Palai..31..421K
7. ↑ https://www.researchgate.net/publication/308792335\_Records\_y\_curiosidades\_de\_los\_dinosaurios\_teropodos\_y\_otros\_dinosauromorfos
8. ↑ https://www.academia.edu/225747
9. ↑ https://ui.adsabs.harvard.edu/abs/2003Natur.421..335X/abstract
10. ↑ https://pubmed.ncbi.nlm.nih.gov/12365352/
11. ↑ https://www.journals.uchicago.edu/doi/abs/10.1086/341993?journalCode=qrb
12. ↑ https://www.science.org/doi/10.1126/science.1145076
13. ↑ https://press.princeton.edu/books/hardcover/9780691167664/the-princeton-field-guide-to-dinosaurs
14. ↑ https://www.semanticscholar.org/paper/Theropod-stress-fractures-and-tendon-avulsions-as-a-Rothschild-Tanke/5ae331f46c1a82ff0c8b7845faa9de3c9fcd4452
15. ↑ https://www.scienceopen.com/document?vid=3ae2eccb-a00b-4f69-b949-ca964c9e66cb
16. ↑ https://www.researchgate.net/publication/308041652\_Depositional\_constraints\_on\_the\_Lower\_Cretaceous\_stikes\_quarry\_dinosaur\_site\_Upper\_yellow\_cat\_member\_cedar\_mountain\_formation\_Utah
17. ↑ https://bioone.org/journals/palaios/volume-31/issue-9/palo.2016.041/DEPOSITIONAL-CONSTRAINTS-ON-THE-LOWER-CRETACEOUS-STIKES-QUARRY-DINOSAUR-SITE/10.2110/palo.2016.041.short
18. ↑ https://www.ksl.com/article/50114561/several-more-utahraptor-fossils-discovered-from-136m-year-old-block-1st-found-in-utah
19. ↑ https://www.sciencedirect.com/science/article/abs/pii/S003101822030225X
20. ↑ https://www.researchgate.net/publication/341124880\_Ontogenetic\_dietary\_shifts\_in\_Deinonychus\_antirrhopus\_Theropoda\_Dromaeosauridae\_Insights\_into\_the\_ecology\_and\_social\_behavior\_of\_raptorial\_dinosaurs\_through\_stable\_isotope\_analysis
21. ↑ https://ui.adsabs.harvard.edu/abs/2020PPP...552j9780F/abstract