Nanosaurus
Encyclopedia
Nanosaurus is the name given to a genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 of dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...

 from the Late Jurassic
Late Jurassic
The Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 161.2 ± 4.0 to 145.5 ± 4.0 million years ago , which is preserved in Upper Jurassic strata. In European lithostratigraphy, the name "Malm" indicates rocks of Late Jurassic age...

. Described by Othniel Charles Marsh
Othniel Charles Marsh
Othniel Charles Marsh was an American paleontologist. Marsh was one of the preeminent scientists in the field; the discovery or description of dozens of news species and theories on the origins of birds are among his legacies.Born into a modest family, Marsh was able to afford higher education...

 in 1877, it is a poorly-known ornithischia
Ornithischia
Ornithischia or Predentata is an extinct order of beaked, herbivorous dinosaurs. The name ornithischia is derived from the Greek ornitheos meaning 'of a bird' and ischion meaning 'hip joint'...

n of uncertain affinities. Its fossils are known from the Morrison Formation
Morrison Formation
The Morrison Formation is a distinctive sequence of Late Jurassic sedimentary rock that is found in the western United States, which has been the most fertile source of dinosaur fossils in North America. It is composed of mudstone, sandstone, siltstone and limestone and is light grey, greenish...

 of Colorado
Colorado
Colorado is a U.S. state that encompasses much of the Rocky Mountains as well as the northeastern portion of the Colorado Plateau and the western edge of the Great Plains...

 and possibly Wyoming
Wyoming
Wyoming is a state in the mountain region of the Western United States. The western two thirds of the state is covered mostly with the mountain ranges and rangelands in the foothills of the Eastern Rocky Mountains, while the eastern third of the state is high elevation prairie known as the High...

. 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
Othnielosaurus
Othnielosaurus 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...

or Othnielia
Othnielia
Othnielia is a genus of ornithischian dinosaur, named after its original describer, Professor Othniel Charles Marsh, an American paleontologist of the 19th century...

.

History and taxonomy

Marsh named three species of his new genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 in 1877, two of which are today known to be dinosaurian:
  • N. agilis, based on YPM 1913, found by school intendant Oramel Lucas, with remains including impressions of a dentary, and postcrania
    Postcrania
    Postcrania[p] in zoology and vertebrate paleontology refers to all or part of the skeleton apart from the skull. Frequently, fossil remains, e.g...

    l bits including an ilium
    Ilium (bone)
    The ilium is the uppermost and largest bone of the pelvis, and appears in most vertebrates including mammals and birds, but not bony fish. All reptiles have an ilium except snakes, although some snake species have a tiny bone which is considered to be an ilium.The name comes from the Latin ,...

    , thigh bones
    Femur
    The femur , or thigh bone, is the most proximal bone of the leg in tetrapod vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles such as lizards, and amphibians such as frogs. In vertebrates with four legs such as dogs and horses, the femur is found only in...

    , shin bones
    Tibia
    The tibia , shinbone, or shankbone is the larger and stronger of the two bones in the leg below the knee in vertebrates , and connects the knee with the ankle bones....

    , and a fibula;
  • N. rex
    Othnielia
    Othnielia is a genus of ornithischian dinosaur, named after its original describer, Professor Othniel Charles Marsh, an American paleontologist of the 19th century...

    , based on YPM 1915 (also called 1925 in Galton, 2007), a complete thigh bone;
  • and N. victor
    Hallopus
    Hallopus was a prehistoric reptile, classified by O. C. Marsh in 1881 as a dinosaur. In fact it was probably a crocodilian or possibly a more primitive crurotarsan, and may be closely related to Junggarsuchus ....

    , which he soon recognized to be something completely different, and is now known as the small, bipedal crocodylian relative Hallopus
    Hallopus
    Hallopus was a prehistoric reptile, classified by O. C. Marsh in 1881 as a dinosaur. In fact it was probably a crocodilian or possibly a more primitive crurotarsan, and may be closely related to Junggarsuchus ....

    .

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
Peter Galton
Peter M. Galton is a British vertebrate paleontologist working in America, who has to date written or co-written about a hundred papers in scientific journals or chapters in paleontology textbooks, especially on ornithischian and prosauropod dinosaurs.With Robert Bakker in a joint article...

 and Jim Jenson
James A. Jensen
James A. Jensen , was an American paleontologist. His extensive collecting program at BYU in the Utah-Colorado region which spanned 23 years was comparable in terms of the number of specimens collected to that of Barnum Brown during the early 20th century. He was given the name "Dinosaur Jim"...

 described a partial skeleton (BYU ESM 163
Brigham Young University
Brigham Young University is a private university located in Provo, Utah. It is owned and operated by The Church of Jesus Christ of Latter-day Saints , and is the United States' largest religious university and third-largest private university.Approximately 98% of the university's 34,000 students...

 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
Othnielia
Othnielia is a genus of ornithischian dinosaur, named after its original describer, Professor Othniel Charles Marsh, an American paleontologist of the 19th century...

for N. rex. He referred Nanosaurus proper to the nebulous "Fabrosauridae
Fabrosauridae
The Fabrosauridae was originally proposed by Galton , as a group of basal ornithischian dinosaurs from the Early to Middle Jurassic. However, recent studies indicate the Fabrosaurs are not a natural grouping of dinosaurs, and instead consist of unrelated genera.The proposed "Fabrosaurs" descended...

", but other authors, including Paul Sereno
Paul Sereno
Paul Callistus Sereno is an American paleontologist from the University of Chicago who discovered several new dinosaur species on several continents. He has conducted excavations at sites as varied as Inner Mongolia, Argentina, Morocco, and Niger...

, regarded it as a dubious
Nomen dubium
In zoological nomenclature, a nomen dubium is a scientific name that is of unknown or doubtful application...

 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
Heterodontosauridae
Heterodontosauridae is a family of early ornithischian dinosaurs that were likely among the most basal members of the group...

 in the thigh bone. He also tentatively assigned to it some teeth that had been referred to Drinker
Drinker
Drinker was a genus of hypsilophodont dinosaur from the late Jurassic period of North America. Although based on good remains, it remains obscure due to a lack of post-naming publications.-Description:...

.

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, biped
Biped
Bipedalism is a form of terrestrial locomotion where an organism moves by means of its two rear limbs, or legs. An animal or machine that usually moves in a bipedal manner is known as a biped , meaning "two feet"...

al, cursorial
Cursorial
Cursorial is a biological term that describes an organism as being adapted specifically to run. It is typically used in conjunction with an animal's feeding habits or another important adaptation. For example, a horse can be considered a "cursorial grazer", while a wolf may be considered a...

 animal, probably an herbivore
Herbivore
Herbivores are organisms that are anatomically and physiologically adapted to eat plant-based foods. Herbivory is a form of consumption in which an organism principally eats autotrophs such as plants, algae and photosynthesizing bacteria. More generally, organisms that feed on autotrophs in...

.
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