Utahraptor

Premaxilla of BYU 7510 14585

The first specimens of Utahraptor were found in 1975 by Jim Jensen in the Dalton Wells Quarry of Utah, near the town of Moab, but did not receive much attention. After a find of a large claw by Carl Limone in October of 1991, James Kirkland, Robert Gaston, and Donald Burge uncovered further remains of Utahraptor in 1991 in the Gaston Quarry in Grand County, Utah, within the Yellow Cat and Poison Strip members of the Cedar Mountain Formation. The holotype of Utahraptor, CEUM 184v.86, consists of a second pedal ungual, with potentially assigned elements from other specimens: pedal ungual CEUM 184v.294, tibia CEUM 184v.260, and premaxilla CEUM 184v.400.[1] The holotype is housed in the paleontology collections of the Prehistoric Museum at Utah State University Eastern. Brigham Young University, the depository of Jensen's finds, currently houses the largest collection of Utahraptor fossils.

The type species, Utahraptor ostrommaysi, was named by Kirkland, Gaston, and Burge in June 1993. The genus name Utahraptor is in reference to Utah, where the remains were found. The specific name, ostrommaysi, is in honor to John Ostrom for his investigations on Deinonychus and its relationships to birds, as well as Chris Mays, who helped in the research of Utahraptor by founding Dinamation.[1] From his description, Kirkland stated the meaning of genus name to be "Utah's predator,"[1] but the Latin word raptor translates to 'robber' or 'plunderer', not 'predator'.[2] Earlier, it had been intended to name the species "U. spielbergi" after film director Steven Spielberg, in exchange for him funding paleontological research, but no agreement could be reached on the amount of financial assistance.[3]

Pedal ungual II of CEUM 184v.294, housed at the Prehistoric Museum, USU Eastern.

In 2000, the specific name was emended by George Olshevsky to the plural genitive ostrommaysorum.[4] However, Thiago Vernaschi V. Costa and Normand David in 2019 criticized the use of the species name U. ostrommaysorum, since it has no clear justification or explanation. Although this spelling has been largely used by other authors, the genus Utahraptor was originally coined with the type species U. ostrommaysi and, given that the International Code of Zoological Nomenclature offers no provision for forming a genitive form from two persons with different names, Costa and David conclude that the original spelling ostrommaysi has to be regarded as an arbitrary combination of letters and not a correctly formed genitive form. Under this reasoning, ostrommaysorum has no valid use and the original spelling ostrommaysi does not need to be emended. Other alternative and also invalid spellings were used in scientific literature, such as ostromaysi, ostromaysorum, ostromayssorum, ostromayorum and ostrommaysori.[5]

For instance, some elements were wrongly referred to the genus. The lacrimal bone of the specimen CEUM 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 M184v.294, BYU 9438, and BYU 13068 are indeed pedal unguals.[6] This suggestion was confirmed by Senter in 2007.[7]

Utahraptor specimens compared in size to a 1.8 m (5.9 ft) tall human

Utahraptor was one of, if not the largest and heaviest of all dromaeosaurids, with the largest assigned specimen (BYUVP 15465, with a femoral length of ~60 cm (24 in)) estimated around 4.9 m (16 ft) long, 1.5 m (4.9 ft) tall at the hips and 280–300 kg (620–660 lb) in weight.[8][9]

Upon the description of Utahraptor, its dimensions were estimated as much as 7 m (23 ft) in length and somewhat less than 500 kg (1,100 lb), comparable in weight to a polar bear.[1] Various authors, such as Gregory S. Paul, agree in that Utahraptor is best estimated around 5.5 m (18 ft) long and weighing up to 300 kg (660 lb).[10]

Life restoration

Although feathers have never been found in association with Utahraptor specimens, there is strong phylogenetic evidence suggesting that all dromaeosaurids had them. The feathered genus Microraptor is one of the oldest-known dromaeosaurids and is phylo­genetically more primitive than Utahraptor.[11] 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.[12] So far, there is nothing to suggest that feathers were lost in larger, more derived species of dromaeosaurs.[13] The presence of quill knobs in Dakotaraptor evidenced that even larger dromaeosaurids had feathers.[14]

Reconstructed skull, BYU

According to Kirkland et al. in 1993, Utahraptor can be recognized by a few special autapomorphies. The claws on its hand are more specialized as cutting blades than in other dromaeosaurids. It has a lacrimal bone with distinctly parallel mesial and outer sides that gives it an elongate subrectangular appearance in top view and it has a base of the nasal opening on the premaxilla parallel to the premaxillary tooth row.[1] In the revised diagnosis conducted by Turner et al. in 2012, Utahraptor differs from other dromaeosaurids in having 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.[15] Like other dromaeosaurids, Utahraptor had a large curved claw on the second toe of each foot. The second pedal ungual is preserved at 22 cm (8.7 in) in length and is estimated to reach 24 cm (9.4 in) in restoration.[1]

Utahraptor is a member of the family Dromaeosauridae, a clade of theropod dinosaurs commonly known as "raptors". Utahraptor is the largest known genus in the family and belongs to the same clade of other notable dinosaurs such as Velociraptor, Deinonychus, or Dromaeosaurus. It is classified in the subfamily Dromaeosaurinae, which is found in the clade Eudromaeosauria.[1]

In 2015, Utahraptor was found to be closely related to the smaller Dromaeosaurus and the giant Mongolian and North American dromaeosaurid genera Achillobator and Dakotaraptor:[14]

Size of Utahraptor (5) compared with other dromaeosaurs

The cladogram below is the result of a cladistic analysis conducted by Cau et al. in 2017.[16]

Utahraptor lived in the lower part of the Cedar Mountain Formation, a bed known as the Yellow Cat Member. According to the authors of its description, Utahraptor had an important ecological role as a major carnivore of the paleofauna of the present-day Arches region during the Early Cretaceous, and could probably attack prey larger than itself. Group hunting of individuals of at least 3.5 m (11 ft) and 70 kg (150 lb), if proven, could have killed 8 m (26 ft) prey of a weight of 1 to 2 t (2,200 to 4,400 lb). Additionally, sauropods ranging around 20 m (66 ft) may have been an important part of its diet.[1] The paleontologist Thomas R. Holtz estimated that Utahraptor existed between 130 million and 125 million years ago.[21] In multiple occasions, the Yellow Cat Member has been dated to Barremian-Aptian ages. Sames and Schudack (2010) proposed a reassignment of the estimated age, compromising Berriasian to Valanginian stages; however, this interpretation was not followed by most authors.[22] Using advanced methods of radiometric and palynological dating, Joeckel et al. (2019) concluded that the Yellow Cat Member is indeed older that previous estimations. The deposition occurred between 139 ± 1.3 million to 134.6 ± 1.7 million years ago, or, Berriasian to Late Valanginian stages. Based on the presence of new palynoflora, Middle Berriasian–Early Hauterivian ages were provisionally assigned.[23] However, the Yellow Cat Member is divided into distinct "lower" and "upper" layers, and Utahraptor fossils are only currently known within the upper Yellow Cat Member.[24]

Utahraptor (red, right) and other dinosaur fauna from the Cedar Mountain Formation

Utahraptor was unearthed from the Yellow Cat Member, which during the Berriasian to Late Valanginian was a semiarid area with floodplain prairies, riverine forests, and open woodlands predominated by conifers (Pinophyta), ferns (Polypodiopsida), hornworts (Anthocerotophyta) and other vascular plants.[23] During the description of Mierasaurus, it was interpreted that there was also a waterlogged bog-like environment.[25] There is believed to have been a short wet season. This is supported by the presence of charred spores and other carbonized plant debris in the pollen maceral that indicate the occurrence of ancient wildfires ignited during periods of low precipitation.[17][23]

Paleofauna that were contemporaneous with the dromaeosaurid in the upper Yellow Cat Member included numerous dinosaurs, such as the medium-sized iguanodonts Hippodraco and Cedrorestes, the smaller theropods Martharaptor and Nedcolbertia, the nodosaurid Gastonia, and the sauropods Cedarosaurus and Moabosaurus.[25][24][26] The only known mammal from the Upper Yellow Cat Member is Cifelliodon.[27]

Other non-dinosaur or avian taxa known from the Member include the fish Ceratodus and Semionotus, the turtles Glyptops and Trinitichelys, Aquatilavipes (fossilized bird tracks), the rhynchocephalian Toxolophosaurus, and the indeterminate remains of hybodontid and polyacrodontid sharks.[24]

Additional paleofauna was recovered, most of it being unnamed and/or indeterminate, including an isolated mesoeucrocodylian skull that measures 20 cm (7.9 in) in length.[24] A neochoristodere unearthed from the Upper Yellow Cat Member, represented by a partial left femur,[28] shows that aquatic paleofauna was present and diverse during the Early Cretaceous of the Cedar Mountain Formation.[24] A large sail-backed iguanodont represented by large vertebrae and fragmentary remains,[29] and an indeterminate eudromaeosaur known from a caudal vertebra and fragmented tail (UMNH VP 20209) were also present.[30]

Raptor Red was published in 1995, and features the fictionalized story of a female Utahraptor. Written by paleontologist Robert T. Bakker, it was positively regarded by mainstream reviewers, though updates to the science have rendered some of the story line facts presented untrue and the paleontology community was critical of fossil record inaccuracies.[31][32] Bakker's anthropomorphosis of the titular Red was particularly praised.[33][34][35]

In 2018, it was proposed by a 10 year-old elementary school student, Kenyon Roberts, that Utahraptor be the Utah state dinosaur, an act that was approved by the Senate.[36] Initially Utahraptor would have replaced another dinosaur, Allosaurus, as the state's official fossil, but it was decided that Utahraptor would be another symbol of the state.[37] In 2021, Steve Eliason[38][39] successfully created a proposal for Utahraptor State Park where the block was discovered, proposed by the same Utah student, Kenyon Roberts. It was approved by the state House.[40]

• Timeline of dromaeosaurid research

• Media related to Utahraptor at Wikimedia Commons
• Data related to Utahraptor at Wikispecies
• Utahraptor Project page at Facebook
• Utahraptor skeletal reconstruction by Scott Hartman
• 3D Utahraptor skeletal reconstruction at Sketchfab