Fact Sheet For:

Irmis, R.B., Nesbitt, S.J., Padian, K., Smith, N.D., Turner, A.H., Woody, D., and Downs, A. 2007. A Late Triassic Dinosauromorph Assemblage from New Mexico and the Rise of Dinosaurs. Science 317:358-361. (DOI: 10.1126/science.1143325)

What our paper DOES NOT say
Pronunciation Guide
Media Images


1. Dinosaurs lived with their closest relatives towards the end of the Triassic Period.

2. The closest relatives of dinosaurs are known as “basal dinosauromorphs”.

3. The Triassic Period lasted from 250 to 200 million years ago, and the following animals arose during this time: dinosaurs, crocodile relatives, mammals, pterosaurs, turtles, frogs, and lizards.

4. During the Triassic, the continents were coalesced into a single landmass named Pangaea.

5. The fossils described in this paper were found at Ghost Ranch, in northern New Mexico, near the town of Abiquiu. Ghost Ranch is famous for its Triassic fossils, and has been visited throughout the last 130 years by scientists from the University of California – Berkeley, American Museum of Natural History, and the famous paleontologist Edward Drinker Cope.

6. The fossils are from a new locality known as the Hayden Quarry. This locality is probably several million years older than the famous Coelophysis Quarry, also on Ghost Ranch land.

7. The Hayden Quarry is between 210 and 220 million years old.

8. Excavations were started in 2002 at the Hayden Quarry. In 2006, a large-scale excavation for six weeks illuminated the diverse fauna from this site.

9. Most of the animals from the Hayden Quarry are known from complete single bones, not skeletons.

10. Dinosaurs in the Hayden Quarry were found with fishes, amphibians, crocodile-relatives, and basal dinosauromorphs.

11. Dinosaurs found in the Hayden Quarry include Chindesaurus bryansmalli and carnivorous (theropod) dinosaurs.

12. Dromomeron means “running femur”. The femur is the thigh bone. The second part of the species name, romeri, is named after the famous vertebrate paleontologist, Alfred Sherwood Romer.

13. The closest relative of Dromomeron is Lagerpeton, known from the Middle Triassic of Argentina, approximately 235 million years ago.

14. The co-occurrence of dinosaurs with basal dinosauromorphs and crocodile-relatives for at least 15-20 million years demonstrates that the rise of dinosaurs was gradual, not sudden.

15. This is the first locality known where basal dinosauromorphs and dinosaurs are found together.

16. The Hayden Quarry was near the equator during the Late Triassic Period.

17. Low latitude faunas like the Hayden Quarry differed from high latitude faunas (e.g., Europe, Argentina, and South Africa) during the Late Triassic. For example, these low-latitude assemblages lack sauropodomorph dinosaurs (relatives of the long-necked four-legged dinosaurs such as Apatosaurus and Diplodocus).

18. Dinosaurs did not dominate the world until after the Triassic. This was during the Early Jurassic Period, beginning 200 million years ago.

19. Eucoelophysis was once thought to be a carnivorous (theropod) dinosaur, but is now known to be a basal dinosauromorph.

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Our paper DOES NOT say that:

1. Dromomeron is a dinosaur.

2. Dromomeron is the ancestor of dinosaurs.

3. Dromomeron is the direct descendant of Lagerpeton.

4. the Hayden Quarry dinosaurs are the oldest dinosaurs in the world [or North America].

5. dinosaurs definitely did/did not replace basal dinosauromorphs and crocodile-relatives by competition.

6. dinosaurs and/or basal dinosauromorphs originated from North America (or any other geographic location).

7. differences in Late Triassic vertebrate assemblages (e.g., latitudinal disparity) are a result of any particular causal mechanism.

8. the rise of dinosaurs resulted from a meteorite impact.

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Pronunciation Guide:

Dromomeron romeri – Dro-MOE-mer-on RO-mer-eye

Lagerpeton chanarensis – LAG-err-peh-TON sha-NYAR-en-sis

Eucoelophysis – YOU-see-low-PHY-sis

Silesaurus – SIGH-leh-SOAR-us

Chindesaurus bryansmalli – SHIN-dee-SOAR-us BRI-an-SMALL-eye

Coelophysis – SEE-low-PHY-sis

Coelophysoid – SEE-low-phy-SOYD

Dinosauromorph – DIE-no-SOAR-oh-MORPH

Chinle – Chin-LEE

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Media Images:

[Click image for high-resolution version]

Cover Art - Reconstruction of Hayden Quarry animals.

Caption: This scene depicts four dinosaurs and dinosaur precursors from the Hayden Quarry of northern New Mexico. The coexistence during the Late Triassic of the dinosaur precursors Dromomeron romeri (lower left) and a Silesaurus-like animal (bottom center), and the dinosaurs Chindesaurus bryansmalli (top center, with crocodylomorph in its mouth) and a coelophysoid theropod (upper right), indicates that the rise of dinosaurs was prolonged rather than sudden. Artwork by Donna Braginetz. © 2007 University of California Museum of Paleontology.

Skeletal reconstruction of Hayden Quarry animals.

Caption: Skeletal reconstruction of dinosaur precursors and dinosaurs from the Hayden Quarry. The small animal in the lower left foreground is Dromomeron romeri, and the four-legged creature behind it is a Silesaurus-like animal. Dinosaurs include Chindesaurus bryansmalli (to the right, second from the back) and a Coelophysis-like theropod (animal in the far back). Artwork by Donna Braginetz. © 2007 University of California Museum of Paleontology.

Photo of the Hayden Quarry at Ghost Ranch, New Mexico. © 2007 Randall Irmis.

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