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Dentary and ilium of N. agilis
Scientific classification edit
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Order: Ornithischia
Family: Nanosauridae
Marsh, 1877b
Genus: Nanosaurus
Marsh, 1877a
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 based on remains referred to Othnielosaurus.

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,[clarification needed] 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.[citation needed]

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]


  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)". Paläontologische 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. ^ 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