|Left femur of O. rex|
†Othnielia rex (Marsh, 1877)
The type species, Othnielia rex, was originally described as Nanosaurus rex by Marsh (1877) on the basis of YPM 1925, femur found by Marshall Parker Felch at Garden Park, Colorado, in 1875. In a 1977 paper on Late Jurassic "hypsilophodonts", Peter Galton noted that N. rex differed from the Nanosaurus type species in details of the femur and erected Othnielia for it, creating the new combination Othnielia rex. The holotypes of Othnielosaurus consors and "Laosaurus" gracilis" were referred to Othnielia rex.
Galton (2007) considered the holotype femur undiagnostic and thus Othnielia to be a dubious name, revalidating Laosaurus consors and assigning it to the new genus Othnielosaurus, while referring the skeleton BYU 163 from Utah to O. consors. However, Carpenter and Galton (2018) synonymized Othnielia as well as Othnielosaurus with Nanosaurus based on shared characters in the femur.
Kathleen Brill and Kenneth Carpenter reported a baby ornithopod, possibly Othnielia rex from the Morrison Formation at Garden Park, Colorado in 2001. The specimen is catalogued as DMNH 21716. Evidence that DMNH 21716 was not fully grown include its small size, unfused neural arches, and the ends of its long bones are "spongy and incompletely formed." The skeleton itself is about one third the size of a known adult specimen. However, the chronological age of the specimen could not be estimated because Othnielia eggs and hatchlings were unknown. Carpenter and Galton (2018) referred DMNH 21716 to Nanosaurus.
- Marsh (1877).
- Galton, P.M., 1977, The ornithopod dinosaur Dryosaurus and a Laurasia-Gondwanaland connection in the Upper Jurassic: Nature, v. 268, p. 230–232.
- Galton (2007).
- Carpenter and Galton (2018)
- "Abstract," Brill and Carpenter (2001). Page 197.
- "Introduction," Brill and Carpenter (2001). Page 198.
- "Discussion," Brill and Carpenter (2001). Page 404.
- Brill, K.; Carpenter, K. (2001). "A baby ornithopod from the Morrison Formation of Garden Park, Colorado". In Tanke, D.H.; Carpenter, K. (eds.). Mesozoic Vertebrate Life. Bloomington and Indianapolis: Indiana University Press. pp. 197–205. ISBN 978-0-253-33907-2.
- Kenneth Carpenter; Peter M. Galton (2018). "A photo documentation of bipedal ornithischian dinosaurs from the Upper Jurassic Morrison Formation, USA". Geology of the Intermountain West. 5: 167–207.
- Galton, P.M. (1977). The ornithopod dinosaur Dryosaurus and a Laurasia-Gondwanaland connection in the Upper Jurassic. Nature 268: 230-232.
- Galton, P.M. (2007). Teeth of ornithischian dinosaurs (mostly Ornithopoda) from the Morrison Formation (Upper Jurassic) of the western United States. in: Carpenter, K. (ed.). Horns and Beaks: Ceratopsian and Ornithopod Dinosaurs. Indiana University Press: Bloomington, 17-47. ISBN 0-253-34817-X.
- Glut, Donald F. (2006). Dinosaurs: The Encyclopedia, Supplement 4. Jefferson, North Carolina: McFarland & Company, Inc. p. 206. ISBN 978-0-7864-2295-1.
- Marsh, O.C. (1877). Notice of new dinosaurian reptiles from the Jurassic formations. American Journal of Sciences (Series 3) 14:514-516.