DinoDex
Large feathered dromaeosaur with a big sickle claw, in side view
Life restoration of Utahraptor ostrommaysi.Image credit: Fred Wierum, CC BY-SA 4.0, via Wikimedia Commons (unmodified except resizing)CC BY-SA 4.0 (unmodified)Source (opens in a new tab)

Utahraptor ostrommaysi

Pronounced YOO-tah-RAP-tor os-trom-MAY-zeye

Eudromaeosauria · Dromaeosauridae

The largest known dromaeosaurid, a heavily built "raptor" several metres long from the Early Cretaceous Cedar Mountain Formation of Utah, with a sickle claw over 20 cm long.

  • Feathered
  • Bipedal
  • Sickle claw
  • Giant
  • Possible pack behavior
Compare
Period
Cretaceous· Barremian
Diet
Carnivore
Length
5.5–7 m
Mass
Unknown
Location
Utah

Quick answers

How big was Utahraptor ostrommaysi?
Utahraptor ostrommaysi was about 5.5–7 m long. It stood about 1.3–1.6 m tall at the hips. (Kirkland et al. 1993; Paul 2010)
When did Utahraptor ostrommaysi live?
Utahraptor ostrommaysi lived during the Early Cretaceous, about 125.8–121.4 million years ago. (Cohen et al. 2023; Kirkland et al. 1993)
Where have Utahraptor ostrommaysi fossils been found?
Fossils of Utahraptor ostrommaysi have been found in Cedar Mountain Formation (Utah). (Kirkland et al. 1993; Paul 2010)
What did Utahraptor ostrommaysi eat?
Utahraptor ostrommaysi was a carnivore. (Kirkland et al. 1993; Paul 2010)
Who named Utahraptor ostrommaysi, and when?
Utahraptor ostrommaysi was described by James I. Kirkland, Robert Gaston & Donald Burge in 1993. (Kirkland et al. 1993)

On this page

YOO-tah-RAP-tor os-trom-MAY-zeye

Period
Cretaceous125.8–121.4 Ma
Diet
Carnivore
Length
5.5–7 m
Mass
Unknown
Classification
Eudromaeosauria · Dromaeosauridae
Described
1993, James I. Kirkland, Robert Gaston & Donald Burge

Overview

Utahraptor ostrommaysi lived in what is now eastern Utah in the Early Cretaceous. Its remains come from the Yellow Cat Member of the Cedar Mountain Formation. James Kirkland, Robert Gaston and Donald Burge named it in 1993, honouring John Ostrom, who first described Deinonychus, and Chris Mays of Dinamation.

It was the giant of the dromaeosaurids: much heavier and longer than Deinonychus, with a huge sickle claw on each foot. Unlike its lighter relatives it had relatively short, strong legs, suggesting it overpowered prey rather than chasing it over long distances.

In 2001 a sandstone block was found near Moab with the bones of several Utahraptor individuals, from adults to juveniles, mixed with an iguanodont. It may be a quicksand trap that caught a group, but the block is still being prepared and the interpretation is open. The age of the Yellow Cat Member is also debated.

Name meaning

"Utah's plunderer", from Utah and Latin raptor; ostrommaysi honours John Ostrom and Chris Mays (Kirkland, Gaston & Burge 1993).

Biology & evidence

What scientists think about how this animal lived, and how strong the evidence for each idea is.

Locomotion

  • Utahraptor was built for power rather than speed.

    Evidence level: Moderate evidence

    Its lower legs are short and stout compared with lighter relatives, which points to strength over endurance running.

    Evidence for / against · 1
    Evidence for

    • Comparative anatomy · Utahraptor robust hind limbs

      Shorter, sturdier lower legs and a larger sickle claw than in Deinonychus, suggesting power rather than speed.

      Specimen: CEU 184v.86

Feathers

  • Utahraptor had feathers.

    Evidence level: Strong evidence

    Feathers are not preserved with it, but they are known in its close relatives on both sides of the family tree.

    Evidence for / against · 1
    Evidence for

    • Phylogenetic inference · Dromaeosaur quill knobs and feathered relatives

      Close relatives are preserved with feathers, and Velociraptor shows quill knobs; Deinonychus sits inside this feathered group.

Social life

  • Utahraptor lived in family groups.

    Evidence level: Hypothesis

    A block with adults and young together suggests they were together when they died, but the site is still being prepared and a trap could gather unrelated animals.

    Evidence for / against · 1
    Evidence for

Size

Length
5.5–7 m

(23 ft)

Height
1.5 mpublished range 1.3–1.6 m

(4.9 ft)

Based on BYU material and Stikes Quarry specimens

Mass
Unknown
Utahraptor ostrommaysi was about 7 m (23 ft) long, roughly 3.9 times the height of a 1.8 m adult human.

Timeline

Lived from about 125.8 to 121.4 million years ago (Ma), within the Mesozoic era (252–66 Ma).

Periods: Barremian (125.8–121.4 Ma), Early Cretaceous (145–100.5 Ma)

Ages are the ICS 2023/09 bounds of the Barremian, the stage(s) the fossils are assigned to; they bracket the record and are not dated first/last appearances. The Yellow Cat Member is usually cited as Barremian, but some dating work suggests it is older (Valanginian-Hauterivian); the range is uncertain.

Location

Formations

Places

Map data: Natural Earth (public domain). Modern positions, not where the continents were then.

These are the places where fossils have been found, not the full area where the animal lived.

Ecosystem

Lived in: Yellow Cat

floodplain, river system, other

Early Cretaceous semi-arid floodplains with seasonal rivers and springs in what is now eastern Utah. Its age is debated.

Classification

  1. cladeDinosauria
  2. cladeSaurischia
  3. cladeTheropoda
  4. cladeCoelurosauria
  5. cladeManiraptora
  6. familyDromaeosauridae
  7. cladeEudromaeosauria
  8. genusUtahraptor
  9. speciesUtahraptor ostrommaysi

Taxonomic status: Valid

Fossil record

Utahraptor skeleton cast from bones in the Brigham Young University collection, at the BYU Museum of Paleontology.Image credit: Jaren Wilkey, CC BY-SA 4.0, via Wikimedia Commons (unmodified except resizing), BYU Museum of PaleontologyCC BY-SA 4.0 (unmodified)Source (opens in a new tab)
Specimens
Catalog numberStatusInstitutionFound
CEU 184v.86HolotypePrehistoric Museum, Utah State University Eastern (CEU)1991
UGS Utahraptor megablock “Utahraptor megablock”Referred specimenUtah Geological Survey (UGS)2001

What has been found

Holotype: CEU 184v.86

  • Preserved
  • Partial
  • Reconstructed
  • Unknown / not recorded

Holotype: CEU 184v.86

Region by region (table)
Skeleton regions of Holotype: CEU 184v.86
RegionState
SkullUnknown / not recorded
MandibleUnknown / not recorded
TeethUnknown / not recorded
Cervical vertebraeUnknown / not recorded
Dorsal vertebraeUnknown / not recorded
SacrumUnknown / not recorded
Caudal vertebraeUnknown / not recorded
RibsUnknown / not recorded
GastraliaUnknown / not recorded
Scapula / shoulder girdleUnknown / not recorded
HumerusUnknown / not recorded
Forearm (radius / ulna)Unknown / not recorded
Hand (manus)Unknown / not recorded
PelvisUnknown / not recorded
FemurUnknown / not recorded
Tibia / fibulaUnknown / not recorded
Foot (pes)Partial · Second-toe claw.

Referred specimen: UGS Utahraptor megablock “Utahraptor megablock”

Region by region (table)
Skeleton regions of Referred specimen: UGS Utahraptor megablock “Utahraptor megablock”
RegionState
SkullPartial
MandibleUnknown / not recorded
TeethUnknown / not recorded
Cervical vertebraePartial
Dorsal vertebraeUnknown / not recorded
SacrumUnknown / not recorded
Caudal vertebraeUnknown / not recorded
RibsUnknown / not recorded
GastraliaUnknown / not recorded
Scapula / shoulder girdleUnknown / not recorded
HumerusUnknown / not recorded
Forearm (radius / ulna)Unknown / not recorded
Hand (manus)Unknown / not recorded
PelvisUnknown / not recorded
FemurPartial
Tibia / fibulaUnknown / not recorded
Foot (pes)Unknown / not recorded
Skull of the Utahraptor skeleton cast at the BYU Museum of Paleontology.Image credit: Jaren Wilkey, CC BY-SA 4.0, via Wikimedia Commons (unmodified except resizing), BYU Museum of PaleontologyCC BY-SA 4.0 (unmodified)Source (opens in a new tab)

All specimens

Discovery

Year described
1993
Described by
James I. Kirkland, Robert Gaston & Donald Burge
Type specimen
CEU 184v.86

Discovery timeline

  1. 1991 · First material found

    Utahraptor claw found at Gaston Quarry

    A giant foot claw is found in the Cedar Mountain Formation of Utah.

    People: Carl Limoni, Robert Gaston

  2. 1993 · Formally described

    Kirkland, Gaston and Burge name Utahraptor

    The largest known dromaeosaurid is named, the same year Jurassic Park showed oversized raptors.

    People: James I. Kirkland, Robert Gaston

  3. 2001 · Specimen recovered

    Utahraptor megablock found

    A block with several Utahraptor individuals is found near Moab.

    People: Matt Stikes

Sources

  1. Cohen, K. M., Harper, D. A. T., Gibbard, P. L. & Car, N. (2023). International Chronostratigraphic Chart (v2023/09). International Commission on Stratigraphy. https://stratigraphy.org/ICSchart/ChronostratChart2023-09.pdf (opens in a new tab)
  2. Kirkland, J. I., Gaston, R. & Burge, D. (1993). A large dromaeosaur (Theropoda) from the Lower Cretaceous of eastern Utah. Hunteria 2(10): 1-16.
  3. Paul, G. S. (2010). The Princeton Field Guide to Dinosaurs. Princeton University Press.
  4. Paul, G. S. (2016). The Princeton Field Guide to Dinosaurs (2nd edition). Princeton University Press.