Temporal range: Late Triassic, 220–210 Ma
|Hypothetical reconstruction of Dromomeron romeri|
Irmis et al., 2007
Dromomeron (meaning "running femur") is a genus of lagerpetonid dinosauromorph archosaur from Late Triassic-age rocks of the Southwestern United States. It is known from partial remains, largely from the hindlimbs, which indicate an animal with an overall length of less than 1.0 meters (3.3 ft). It is described as most closely related to the earlier Lagerpeton of Argentina, but was found among remains of true dinosaurs like Chindesaurus, indicating that the first dinosaurs did not immediately replace related groups.
Discovery and history
Dromomeron and type species D. romeri is based on GR 218, a complete left thigh bone from the Hayden Quarry at Ghost Ranch, New Mexico. The rocks there are in the lower portion of the Petrified Forest Member of the Chinle Formation, and are Norian in age. Additional hindlimb bones, some probably from the same individual, are also known, and a partial skeleton has been recovered from Hayden Quarry, but has not yet been fully prepared. A few other specimens have been recovered from nearby localities, including the Snyder Quarry. The bones of Dromomeron are most similar to those of the older dinosauromorph Lagerpeton, and the two animals have been classified together in a clade Lagerpetonidae. The species name romeri honors influential 20th century vertebrate paleontologist Alfred Sherwood Romer.
Also found at the Hayden Quarry are the remains of phytosaurs, aetosaurs, rauisuchians, and several types of dinosaurs and dinosaur relatives, including a Silesaurus-like animal, the herrerasaurid Chindesaurus, and the basal theropod Tawa. Finding the remains of four types of dinosaurs and dinosaur relatives (including Dromomeron itself) is noteworthy because it shows that dinosaurs did not immediately replace related groups; that some of these groups, like the lagerpetonids, persisted for longer than previously known and diversified; and that dinosaurian replacement may have occurred at different times in different areas.
Other specimens from the Chinle Formation of Arizona and a roughly contemporaneous part of the Dockum Group of Texas also have been assigned to this genus. These have been assigned to second species D. gregorii, named in 2009.
D. gregorii, named for Joseph T. Gregory, is based on TMM 31100–1306, a right femur (thigh bone) from the Otis Chalk Quarry, Colorado City Formation, (Dockum Group), near Otis Chalk, Texas. Several other limb bones from the quarry, and a partial femur (thigh bone) from the Placerias Quarry of eastern Arizona have been assigned to this species. The rocks D. gregorii is known from are older than those D. romeri has been found in. As with D. romeri, the Otis Chalk Quarry also has at least one specimen of the early dinosaur Chindesaurus.
- Irmis, Randall B.; Nesbitt, Sterling J.; Padian, Kevin; Smith, Nathan D.; Turner, Alan H.; Woody, Daniel; Downs, Alex (2007). "A Late Triassic dinosauromorph assemblage from New Mexico and the rise of dinosaurs". Science 317 (5836): 358–361. doi:10.1126/science.1143325. PMID 17641198.
- Nesbitt, Sterling J.; Irmis, Randall B.; Parker, William G.; Smith, Nathan D.; Turner, Alan H.; Rowe, Timothy (2009). "Hindlimb osteology and distribution of basal dinosauromorphs from the Late Triassic of North America". Journal of Vertebrate Paleontology 29 (2): 498–516. doi:10.1671/039.029.0218.
- Estimate after the scale diagram at the article's press fact sheet.
- Irmis, Randall B.; Nesbitt, Sterling J.; Padian, Kevin; Smith, Nathan D.; Turner, Alan H.; Woody, Daniel; Downs, Alex (2007). "Supporting online material for A Late Triassic dinosauromorph assemblage from New Mexico and the rise of dinosaurs" (PDF). Science. doi:10.1126/science.1143325. Retrieved 2007-07-22.
- Bennett, C.S. (2013). "A Rebuttal to Nesbitt's and Hone's "An external mandibular fenestra and other archosauriform characteristics in basal pterosaurs"" (PDF). International Symposium on Pterosaurs: 19–22.