Nanosaurus

*Nanosaurus agilis*

* Drinker
* Othnielia

### Name Means

"Small lizard/reptile (Nanosaurus)Named after Othniel Charles Marsh (Othnielia)Othniel's lizard/reptile (Othnielosaurus) Named after Edward Drinker Cope (Drinker)"

### Taxon

Genasauria

**Nanosaurus** (meaning "small or dwarf lizard") is a genus of ornithischian dinosaur that lived about 155 to 148 million years ago, during the Late Jurassic-age Morrison Formation of the western United States. It is named in honor of famed paleontologist Othniel Charles Marsh, and was formerly assigned to the genus *Laosaurus*. This genus was coined to hold fossils formerly included in *Othnielia*, which is based on remains that may be too sparse to hold a name; as such, it is part of decades of research to untangle the taxonomy left behind by Marsh and his rival Edward Drinker Cope from the Bone Wars. *Othnielosaurus* has usually been classified as a hypsilophodont, a type of generalized small bipedal herbivore or omnivore, although recent research has called this and the existence of a distinct group of hypsilophodonts into question.

## Description

*Nanosaurus* is known from material from all parts of the body, including two good skeletons, although the skull is still poorly known (note that earlier references use a multitude of names for this material, with most of them since 1977 using *Othnielia rex*). *Othnielosaurus* was a small animal, 2 meters (6.6 ft) or less in length and 10 kilograms (22 lb) or less in weight. It was a bipedal dinosaur with short forelimbs and long hindlimbs with large processes for muscle attachments.[3] The hands were short and broad with short fingers. From the partial type skull and the skull on the possible specimen "Barbara", the head was small. It had small leaf-shaped cheek teeth (triangular and with small ridges and denticles lining the front and back edges), and premaxillary teeth with less ornamentation. Like several hypsilophodont or iguanodont-grade ornithopods such as *Hypsilophodon*, *Thescelosaurus*, and *Talenkauen*, *Othnielosaurus* had thin plates lying along the ribs. Called intercostal plates, these structures were cartilaginous in origin.

## Classification

*Nanosaurus* (previously under the names *Laosaurus*, *Nanosaurus*, and *Othnielia*) has typically been regarded as a hypsilophodont ornithopod, a member of a nebulous and poorly defined group of small, running herbivorous dinosaurs. This was challenged by Robert Bakker et al. in 1990. In their description of the new taxon *Drinker nisti*, they split *Othnielia* into two species (*O. rex* and *O. consors*) and placed "othnieliids" as more basal than hypsilophodontids. With recent analyses suggesting a paraphyletic Hypsilophodontidae, the general idea of "othnielids" as basal to other hypsilophodonts has been supported, although *Drinker* has been controversial because virtually nothing new has been published on it since its description. Other basal ornithopods have sometimes been linked to *Othnielosaurus*, particularly *Hexinlusaurus*, considered by at least one author to be a species of "*Othnielia*", *O. multidens*. New studies concur with the hypothesis that *Othnielosaurus* is more basal than other traditional hypsilophodonts, but go even farther and remove the genus from Ornithopoda and the larger group Cerapoda, which also includes horned dinosaurs and domeheaded dinosaurs.