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Dentary and ilium of N. agilis
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Clade: Dinosauria
Order: Ornithischia
Family: Nanosauridae
Marsh, 1877b
Genus: Nanosaurus
Marsh, 1877a
Species: N. agilis
Binomial name
Nanosaurus agilis
Marsh, 1877

Nanosaurus ("small or dwarf lizard") is the name given to a genus of dinosaur from the Late Jurassic. Described by Othniel Charles Marsh in 1877, it is a poorly known ornithischian of uncertain affinities. Its fossils are known from the Morrison Formation of Colorado and possibly Wyoming. It has often been illustrated in the popular literature (as a "tiny dinosaur"), leaving the impression that more is known about it than actually is. Most representations are actually of what is now called Othnielosaurus or Othnielia.

History and taxonomy[edit]

Marsh named three species of his new genus in 1877, two of which are today known to be dinosaurian:

He regarded both dinosaur species as small ("cat sized"[1] or "fox-sized"[2]) animals.[4] Marsh also named a family for Nanosaurus, Nanosauridae, in which he placed only Nanosaurus.[2]

With the 1881 reassignment of N. victor, matters stood static for most of the next century. Marsh had originally set up Nanosauridae for this genus, but it generally was included in Hypsilophodontidae after his death.

In 1973, Peter Galton and Jim Jenson described a partial skeleton (BYU ESM 163 as of Galton, 2007[5]) missing the head, hands, and tail as Nanosaurus (?) rex.[6] By 1977, he had determined that Nanosaurus agilis was quite different from N. rex and the new skeleton, and coined Othnielia for N. rex.[7] He referred Nanosaurus proper to the nebulous "Fabrosauridae",[8] but other authors, including Paul Sereno, regarded it as a dubious basal ornithischian of unknown affinities,[9] or as a dubious hypsilophodontid.[10] Most recently, Galton (2007) considered it as a possibly valid basal ornithopod, and pointed out similarities with heterodontosaurids in the thigh bone. He also tentatively assigned to it some teeth that had been referred to Drinker.[5]


Because of the few remains, about all that can be said about Nanosaurus in life with any accuracy is that it was a small, bipedal, cursorial animal, probably an herbivore.[10]


  1. ^ a b c Marsh, O.C. (1877a). Notice of some new vertebrate fossils. American Journal of Science (Series 3) 14:249-256.
  2. ^ a b c Marsh, O.C. (1877b). Notice of new dinosaurian reptiles from the Jurassic formations. American Journal of Science (Series 3) 14:514-516.
  3. ^ Marsh, O.C. (1881). "Principal characters of American Jurassic dinosaurs. Part V.". American Journal of Science. 21: 418–423. 
  4. ^ George Olshevsky. "Re: Nanosaurus rex". Retrieved 2007-01-25. 
  5. ^ a b Galton, P.M. (2007). 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, 17-47. ISBN 0-253-34817-X
  6. ^ Galton, P.M.; 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. 
  7. ^ Galton, P.M. (1977). "The ornithopod dinosaur Dryosaurus and a Laurasia-Gondwanaland connection in the Upper Jurassic". Nature. 268 (5617): 230–232. doi:10.1038/268230a0. 
  8. ^ Galton, P.M. (1978). "Fabrosauridae, the basal family of ornithischian dinosaurs (Reptilia: Ornithischia).". Palaeontologische Zeitschrift. 52 (1/2): 138–159. doi:10.1007/bf03006735. 
  9. ^ Sereno, P.C. (1991). "Lesothosaurus, "fabrosaurids," and the early evolution of Ornithischia". Journal of Vertebrate Paleontology. 11 (2): 168–197. doi:10.1080/02724634.1991.10011386. 
  10. ^ a b 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). University of California Press:Berkeley, 392-412. ISBN 0-520-24209-2