Fossils from a quarry in northern New Mexico are helping paleontologists piece together the early history of dinosaurs and their closest relatives, according to a new report in the journal Science.
A team of researchers has uncovered isolated bones of at least four different types of dinosaur and dinosaur-like reptiles that lived side-by-side during the Late Triassic, between 220 and 210 million years ago. The reported finds include:
- Leg and ankle bones from a new species named Dromomeron romeri, “Romer’s Running-femur.” Dromomeron appears to be related to Lagerpeton, a two-foot-long reptile from the Middle Triassic of South America. Dromomeron and Lagerpeton are classified as basal dinosauromorphs, which means that they are more closely related to dinosaurs than they are to any other well-known group, but not by much.
- Several bones (including a partial jaw) from a reptile related to Silesaurus from Eastern Europe. This critter is a basal dinosauriform, more closely related to dinosaurs than Dromomeron, but not a card-carrying member of the Dinosauria proper.
- A femur referable to Chindesaurus bryansmalli, known from other material from Arizona’s Petrified Forest. Chindesaurus is thought to be a basal dinosaur (or a basal lizard-hipped dinosaur) related to the South American Herrerasaurus.
- And finally, leg elements of a Coelophysis-like theropod, a definite, unambiguous dinosaur in good standing.
This mix of “basal dinosauromorphs, basal dinosauriforms, basal dinosaurs, and basal theropods,” as Doctor Vector put it, has never before been observed in a single site. This suggests the rise of dinosaurs was more complicated than previously thought. Earlier finds seemed to indicate that the first dinosaurs replaced their predecessors within a relatively short amount of time. Now it appears that several groups near the base of the dinosaur family tree co-existed for several million years before the precursors of the dinosaurs were left in the dust.
Further reading:
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 v. 317, no. 5836, pp. 358–361. doi: 10.1126/science.1143325.
Artist Donna Braginetz painted this cast of characters for the cover of this week’s Science, but a much larger version (and skeletal size comparison) is available from the LiveScience news story.
The press release from UC Berkeley.
Randy Irmis’ Field Notes from the Hayden Quarry.
The story at National Geographic and Ask Doctor Vector.
Update 7/21: More on the Hayden Quarry dinosauromorphs at Tetrapod Zoology.
—Matt Celeskey.
File under: Dinosaurs, Recent Discoveries, Reptiles, Triassic.
Comments on record: (1)