Othnielosaurus
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| Othnielosaurus consors Galton, 2006 |
Othnielosaurus is the name given to a genus of ornithischian dinosaur from the Upper Jurassic of the western United States. It is named in honor of famed paleontologist O.C. Marsh, and was formerly referred to Laosaurus consors. It is intended to replace Othnielia.
In older dinosaur books, Nanosaurus is usually given as the name for a small, bipedal herbivore that is actually based on Othnielia (=Othnielosaurus) material (or is almost completely imaginary).
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[edit] Taxonomy and History
O.C. Marsh named several species and genera in the late 1800s that have come to be recognized as basal ornithopods ("hypsilophodonts"), including Nanosaurus agilis (possibly), "N." rex, Laosaurus celer, L. consors, and L. gracilis.
In 1877, Marsh named two species of Nanosaurus in separate publications, based on partial remains from the Morrison Formation (late Jurassic, Oxfordian-Tithonian) of Garden Park, Colorado: N. agilis (Marsh, 1877a), based on YPM 1913, with remains including impressions of a dentary, and postcranial bits including an ilium, femorae, tibiae, and a fibula; and N. rex, a second species which he based on YPM 1915 (also called 1925 in Galton, 2006), a complete femur. He regarded both species as small ("fox-sized" [Marsh, 1877b]) animals. (A third species, N. victor [Marsh 1977a], was quickly reassessed and became the type of Hallopus, now known to be a small, bipedal crocodylian.) He assigned this genus to the Nanosauridae, but after his death it was transferred to the Hypsilophodontidae.
The next year, he named the new genus Laosaurus on material collected by Samuel Williston from Como Bluff, Wyoming. Two species were named: the type species L. celer, based on vertebrae (YPM 1875, which according to White (1973) consists of two complete vertebral centra and nine partials; Marsh also mentioned some pedal phalanges); and the "smaller" L. gracilis, originally based on a dorsal (lumbar in humans) centrum, a caudal centrum, and part of an ulna (review by Galton [1983] finds the type to now consist of thirteen dosal and eight caudal centra, and portions of both hindlimbs). Gilmore (1909) referred a juvenile femur (USNM 5808) and (1925) a partial skeleton (CM 11340) to L. gracilis, based on size, but Galton (1983) referred the femur to Othnielia and the skeleton to Dryosaurus.
A third species, L. consors, was established by Marsh in 1894 for YPM 1882, which consists of most of one articulated skeleton and part of at least one other individual. The skull was only partially preserved, and the fact that the vertebrae were represented only by centra suggests a partially-grown individual. Galton (1983) notes that much of the current mounted skeleton was restored in plaster, or had paint applied. Again, the genus was assigned to Hypsilophodontidae. (A fourth species, L. altus (Marsh 1878), was renamed by Marsh in 1894 as the type species of Dryosaurus, a well-known basal iguanodontian.)
These animals attracted little professional attention until the 1970s and 1980s, when Peter Galton reviewed many of the "hypsilophodonts" in a series of papers. In 1973, he and Jim Jenson described a partial skeleton (BYU ESM 163 as of Galton, 2006) missing the head, hands, and tail as Nanosaurus (?) rex (as mentioned in the paper, it was damaged by other collectors prior to description). By 1977, he had determined that Nanosaurus agilis was quite different from N. rex and the new skeleton, and coined Othnielia for N. rex. Nanosaurus agilis was referred at various times to the "Fabrosauridae" or Hypsilophodontidae, but due to the poorness of the material has never had a stable position; Galton (2006) considers it a possibly valid basal ornithopod. The 1977 reference, somewhat buried in a paper concerning the transcontinental species of Dryosaurus did not elaborate, but did refer Laosaurus consors and L. gracilis to the new genus, and considered L. celer a nomen nudum. In 1983, he expanded on this with illustrations of much of the material in question.
In 1990, another taxon, Drinker nisti, was added to the situation by Bakker, Galton, Siegwarth, and Filla. Othnielia was split into two species (O. consors) being the new one, and the placement of "othnieliids" as more basal than hypsilophodontids was put forth. While the first idea was not generally accepted, the second was, and throughout the 1990s and early 2000s there was a general consensus that Drinker and Othnielia were closely related to each other and more basal than the traditional hypsilophodonts. With recent analyses suggesting a paraphyletic Hypsilophodontidae (Scheetz, 1998; Winkler, Murry, and Jacobs, 1998; Buchholz, 2002; Weishampel, Jianu, Csiki, and Norman, 2003; Norman, Sues, Witmer, and Coria, 2004), this general idea has been supported, although Drinker has been controversial because virtually nothing new has been published on it since its description, despite good material. Other basal ornithopods have sometimes been linked to it (Phyllodon [Galton, 2006] and Hexinlusaurus [Paul, 1996 {who considered it to be a species of "Othnielia", O. multidens}, Buchholz, 2002], especially).
Finally, in 2006 Galton reevaluated the Morrison ornithischians and concluded that the femur on which Nanosaurus rex is based is not diagnostic, and reassigned the BYU skeleton to Laosaurus consors, which is based on more diagnostic material. In short, for all intents and purposes, Othnielia is now Othnielosaurus consors. Nanosaurus agilis is a possible basal ornithopod, "N." rex is a dubious basal ornithopod, Laosaurus consors is the type species for Othnielosaurus, L. celer is still considered dubious (Norman et al., 2004), L. gracilis was not addressed, and Drinker nisti is its own valid taxon of basal ornithopod.
[edit] Paleobiology
Like other "hypsilophodonts", Othnielosaurus was a small (2 m [6.56 ft] or shorter in length; estimated by Foster [2003] to be 10 kg [22 lb] or less in mass) bipedal dinosaur with short forelimbs and long hindlimbs with attachments for strong running muscles [1]. From the partial type skull and the skull on the possible specimen "Barbara", the head was small, with small leaf-shaped cheek teeth (triangular and with small ridges and denticles lining the front and back edges), and premaxillary teeth with less ornamentation. There would have been a short beak at the tips of the jaws, with a horny covering. The hands were short and broad with short fingers. Typically, it has been interpreted as a small, cursorial herbivore, although Bakker (1986) interpreted the possibly related Nanosaurus as an omnivore. This idea has had some unofficial support [2], but little in the formal literature.
[edit] Other Specimens
Othnielosaurus is known from material from all parts of the body, although the skull is still poorly known. Besides the type material of Laosaurus consors and the BYU specimen, a nearly complete specimen in the Aathal Museum nicknamed "Barbara" is probably referable, as well as some juvenile remains (DMNH 21716, a partial skeleton tentatively referred by Brill and Carpenter [2001] to Othnielia rex), giving it a distribution of Utah, Wyoming, and Colorado. Skeletons are also on display at the Denver Museum of Nature and Science.
A photo of a skull described as Nanosaurus or Othnielia has a great deal of recontruction and may be based on the skull from CM 11340, the "Laosaurus gracilis" specimen considered by Galton to be a juvenile Dryosaurus.
[edit] References
- Bakker, R.T. 1986. The Dinosaur Heresies. William Morrow: New York. 481 pp.
- Bakker, R.T., Galton, P.M., Siegwarth, J., and Filla, J. 1990. A new latest Jurassic vertebrate fauna, from the highest levels of the Morrison Formation at Como Bluff, Wyoming. Part IV. The dinosaurs: A new Othnielia-like hypsilophodontoid. Hunteria 2(6): 8-14.
- Brill, K., and Carpenter, K. 2001. A baby ornithopod from the Morrison Formation of Garden Park, Colorado, in: D. H. Tanke and K. Carpenter (eds.), Mesozoic Vertebrate Life'.' Indiana University Press: Bloomington and Indianapolis, 197-205.
- Buchholz, P.W. 2002. Phylogeny and biogeography of basal Ornithischia, in: The Mesozoic in Wyoming, Tate 2002. The Geological Museum, Casper College: Casper, Wyoming, pp. 18-34.
- Foster, J.R. 2003. Paleoecological Analysis of the Vertebrate Fauna of the Morrison Formation (Upper Jurassic), Rocky Mountain Region, U.S.A. Albuquerque, New Mexico: New Mexico Museum of Natural History and Science. Bulletin 23.
- Galton, P.M. 1977. The ornithopod dinosaur Dryosaurus and a Laurasia-Gondwanaland connection in the Upper Jurassic. Nature 268: 230-232.
- Galton, P.M. 1983. The cranial anatomy of Dryosaurus, a hypsilophodontid dinosaur from the Upper Jurassic of North America and East Africa, with a review of hypsilophodontids from the Upper Jurassic of North America. Geologica et Palaeontologica 17: 207-243.
- Galton, P.M. 2006. Teeth of ornithischian dinosaurs (mostly Ornithopoda) from the Morrison Formation (Upper Jurassic) of the western United States, in: K. Carpenter (ed.), Horns and Beaks: Ceratopsian and Ornithopod Dinosaurs. Indiana University Press: Bloomington and Indianapolis, pp. 17-47.
- Galton, P.M., and Jensen, J.A. 1973. Skeleton of a hypsilophodontid dinosaur (Nanosaurus (?) rex) from the Upper Jurassic of Utah. Brigham Young University Geology Series 20: 137-157.
- Gilmore, C.W. 1909. A new rhynchocephalian reptile from the Jurassic of Wyoming, with notes on the fauna of "Quarry 9." Proceedings of the U.S. National Museum 37: 35-42.
- Gilmore, C.W. 1925. Osteology of ornithopodous dinosaurs from the Dinosaur National Monument, Utah. Memoir of the Carnegie Museum 10: 385-409.
- Marsh, Othniel Charles. 1877a. Notice of some new vertebrate fossils. American Journal of Science (Series 3) 14: 249-256.
- Marsh, O.C. 1877b. Notice of new dinosaurian reptiles from the Jurassic formations. American Journal of Science (Series 3) 14: 514-516.
- Marsh, O.C. 1878. Principle characters of American Jurassic dinosaurs. American Journal of Science (Series 3) 16: 411-416.
- Marsh, O.C. 1894. The typical Ornithopoda of the American Jurassic. American Journal of Science (Series 3) 48: 85-90.
- Norman, D.B., Sues, H.-D., Witmer, L.M., and Coria, R.A. 2004. Basal Ornithopoda, in: Weishampel, D.B., Dodson, P., and Osmólska, H., (eds), The Dinosauria (second edition). Berkeley and Los Angeles: University of California Press, pp. 392-412.
- Paul, G.S. 1996. The complete illustrated guide to dinosaur skeletons. Gakken Mook: Tokyo, 98 p.
- Scheetz, R.D. 1998. Phylogeny of basal ornithopod dinosaurs and the dissolution of the Hypsilophodontidae. Journal of Vertebrate Paleontology 18(3, Suppl.): 75A.
- Weishampel, D.B., Jianu, C.-M., Csiki, Z., and Norman, D.B. 2003. Osteology and phylogeny of Zalmoxes (n.g.), an unusual euornithopod dinosaur from the latest Cretaceous of Romania. Journal of Systematic Palaeontology 1(2): 1-56.
- White, T.E. 1973. Catalogue of the genera of dinosaurs. Annals of Carnegie Museum 44: 117-155.
- Winkler, D.A., Murry, P.A., and Jacobs, L.L. 1998. The new ornithopod dinosaur from Proctor Lake, Texas, and the deconstruction of the family Hypsilophodontidae. Journal of Vertebrate Paleontology 18(3, Suppl.): 87A.
