Arstanosaurus was 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 hadrosaurid

Hadrosaurid

Hadrosaurids or duck-billed dinosaurs are members of the family Hadrosauridae, and include ornithopods such as Edmontosaurus and Parasaurolophus. They were common herbivores in the Upper Cretaceous Period of what are now Asia, Europe and North America. They are descendants of the Upper...

 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 Santonian

Santonian

The Santonian is an age in the geologic timescale or a chronostratigraphic stage. It is a subdivision of the Late Cretaceous epoch or Upper Cretaceous series. It spans the time between 85.8 ± 0.7 mya and 83.5 ± 0.7 mya...

-Campanian

Campanian

The Campanian is, in the ICS' geologic timescale, the fifth of six ages of the Late Cretaceous epoch . The Campanian spans the time from 83.5 ± 0.7 Ma to 70.6 ± 0.6 Ma ...

-age Upper Cretaceous Bostobinskaya Formation, Kazakhstan

Kazakhstan

Kazakhstan , officially the Republic of Kazakhstan, is a transcontinental country in Central Asia and Eastern Europe. Ranked as the ninth largest country in the world, it is also the world's largest landlocked country; its territory of is greater than Western Europe...

. It has had a confusing history, being considered both a hadrosaurid and a ceratopsid, or both at the same time (chimeric

Chimera (paleontology)

In paleontology, a chimera is a fossil which was reconstructed with elements coming from more than a single species of animal. A now classic example of chimera is Protoavis.-List of paleontological chimeras:*Brontosaurus*Lametasaurus...

).

History

The genus was based on a maxilla

Maxilla

The maxilla is a fusion of two bones along the palatal fissure that form the upper jaw. This is similar to the mandible , which is also a fusion of two halves at the mental symphysis. Sometimes The maxilla (plural: maxillae) is a fusion of two bones along the palatal fissure that form the upper...

 (AAIZ 1/1), with a femur

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...

 possibly referable. This is not much material for naming a new genus, and it was largely ignored until the mid 1990s, when the hypothesis that it was really a ceratopsid appeared. Shortly thereafter, a new revision appeared that showed that the characteristics listed as unusual for Arstanosaurus were really based on perspective, and that the maxilla was from an animal like Bactrosaurus

Bactrosaurus

Bactrosaurus is a genus of herbivorous dinosaur that lived in east China during the late Cretaceous, about 70 mya. The position Bactrosaurus occupies in the Cretaceous makes it one of the earliest known hadrosaurs, and although it is not known from a full skeleton, Bactrosaurus is one of the best...

, albeit indeterminate (a dubious name

Nomen dubium

In zoological nomenclature, a nomen dubium is a scientific name that is of unknown or doubtful application...

). The femur was uninformative.
It was regarded as an indeterminate hadrosaurid in the most recent review.

A juvenile

Juvenile (organism)

A juvenile is an individual organism that has not yet reached its adult form, sexual maturity or size. Juveniles sometimes look very different from the adult form, particularly in terms of their colour...

 skeleton from Mongolia

Mongolia

Mongolia is a landlocked country in East and Central Asia. It is bordered by Russia to the north and China to the south, east and west. Although Mongolia does not share a border with Kazakhstan, its western-most point is only from Kazakhstan's eastern tip. Ulan Bator, the capital and largest...

 has been attributed to Arstanosaurus, but on what grounds is unknown. It is under study. It was formerly called "Gadolosaurus

Gadolosaurus

"Gadolosaurus" is the informal name given to a genus of ornithopod dinosaur from late Cretaceous-age rocks in Mongolia. Though the name was made public in 1979, it has never been formally described, and the name is considered a nomen nudum. The name "Gadolosaurus" first appeared in a book by...

".

Paleobiology

As a hadrosaurid, Arstanosaurus would have been a 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/quadrupedal 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...

, eating plants with sets of ever-replacing teeth stacked on each other.

External links

• Arstanosaurus in The Dinosaur Encyclopaedia at Dino Russ's Lair