Nanosaurus

Nanosaurus
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Sauropsida
Superorder:	Dinosauria
Order:	Ornithischia
Suborder:	Cerapoda
Infraorder:	Ornithopoda
Family:	Hypsilophodontidae?
Genus:	Nanosaurus Marsh, 1877
Binomial name
Nanosaurus agilis

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

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

• N. agilis, based on YPM 1913, with remains including impressions of a dentary, and postcranial bits including an ilium, thigh bones, shin bones, and a fibula;
• N. rex, based on YPM 1915 (also called 1925 in Galton, 2007), a complete thigh bone;
• and N. victor, which he soon recognized to be something completely different, and is now known as the small, bipedal crocodylian relative Hallopus.

He regarded both dinosaur species as small ("cat sized" or "fox-sized") animals.

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) missing the head, hands, and tail as Nanosaurus (?) rex. By 1977, he had determined that Nanosaurus agilis was quite different from N. rex and the new skeleton, and coined Othnielia for N. rex. He referred Nanosaurus proper to the nebulous "Fabrosauridae", but other authors, including Paul Sereno, regarded it as a dubious basal ornithischian of unknown affinities, or as a dubious hypsilophodontid. 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.

Paleobiology

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.