# Utahraptor ostrommaysi

> 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.

- Classification: Dinosauria (clade) > Saurischia (clade) > Theropoda (clade) > Coelurosauria (clade) > Maniraptora (clade) > Dromaeosauridae (family) > Eudromaeosauria (clade) > Utahraptor (genus) > Utahraptor ostrommaysi (species)
- Length: 5.5–7 m
- Hip height: 1.3–1.6 m
- Age: 125.8–121.4 million years ago (Early Cretaceous)
- Fossils found in: Cedar Mountain Formation (Utah)
- Diet: carnivore
- Described: James I. Kirkland, Robert Gaston & Donald Burge, 1993

Canonical page: https://dinodex.club/dinosaurs/utahraptor-ostrommaysi
Last updated: 2026-09-27

## 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).

## 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
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.

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Cite as: "Utahraptor ostrommaysi". DinoDex. https://dinodex.club/dinosaurs/utahraptor-ostrommaysi (updated 2026-09-27).