Khurendukhosaurus is 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 choristodere

Choristodera

Choristodera is an order of semi-aquatic diapsid reptiles which ranged from the Middle Jurassic, or possibly Late Triassic, to at least the early Miocene. Choristoderes have been found in North America, Asia, and Europe. The most common fossils are typically found from the Late Cretaceous to the...

, a type of amphibious reptile. It is known from Lower Cretaceous rocks of 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...

 and Russia

Russia

Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...

. Two species have been named. The type species

Type species

In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...

, K. orlovi, was named in 1984 by Sigogneau–Russell and Efimov for the fragmentary 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 skeleton PIN 3386/3. This specimen was discovered in the Aptian

Aptian

The Aptian is an age in the geologic timescale or a stage in the stratigraphic column. It is a subdivision of the Early or Lower Cretaceous epoch or series and encompasses the time from 125.0 ± 1.0 Ma to 112.0 ± 1.0 Ma , approximately...

-age Lower Cretaceous Hühteeg Formation at Hüren Dukh, central 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...

. The lake deposits at this site also contain fossils of the choristoderes Irenosaurus

Irenosaurus

Irenosaurus is a genus of choristodere, a type of amphibious reptile. It is known from a single fragmentary postcranial skeleton , discovered in the Aptian-age Lower Cretaceous Hühteeg Formation at Hüren Dukh, central Mongolia. The type species is I...

and Tchoiria

Tchoiria

Tchoiria is a genus of simoedosaurid choristodere, a type of crocodile-like aquatic reptile. Fossils of this genus have been found in Early Cretaceous-age rocks in Mongolia. Four species have been named, but two have been given their own genera. The type species is T...

. Other postcranial bones of K. orlovi have been found at this site as well.

Second species K. bajkalensis was named by Efimov in 1996 for PIN 2234/201, consisting of a scapulocoracoid

Scapulocoracoid

The Scapulocoracoid is the unit of the pectoral girdle that contains the coracoid and scapula.The coracoid itself is a beak-shaped bone that is commonly found in most vertebrates with a few exceptions.The scapula is commonly known as the shoulder blade...

 and a rib. These bones were found in the Lower Cretaceous Murtoi Formation

Murtoi Formation

The Murtoi Formation is a Mesozoic geologic formation. Dinosaur remains diagnostic to the genus level are among the fossils that have been recovered from the formation.-See also:* List of dinosaur-bearing rock formations...

 at Lake Gusinoye

Lake Gusinoye

Lake Gusinoye is the name of a body of fresh water in the Republic of Buryatia, Russia. It is located about 120 kilometers from Ulan-Ude, the capital of the republic, and is close to the border with Mongolia. The town of Gusinoozyorsk is located on the northeastern shore of the lake...

, Buryatia, Russia

Russia

Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...

. The first Russian choristodere, Efimov and Storrs (2000) found it difficult to distinguish from K. orlovi based on the small amount of material. Skutschas (2008) reported on additional material which supported the placement of the Russian taxon within Khurendukhosaurus, but found the species K. bajkalensis to be dubious

Nomen dubium

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

 within the genus.

Khurendukhosaurus was a small choristodere, approximately 1 metres (3.3 ft) long at most. Efimov and Storrs regarded it as a basal

Basal (phylogenetics)

In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...

 member of Choristodera, but Skutschas was unable to confirm this in a phylogenetic analysis

Cladistics

Cladistics is a method of classifying species of organisms into groups called clades, which consist of an ancestor organism and all its descendants . For example, birds, dinosaurs, crocodiles, and all descendants of their most recent common ancestor form a clade...

. It may have been related to the hyphalosaurids, a group of long–necked choristoderes. The neural spines

Spinous process

The spinous process of a vertebra is directed backward and downward from the junction of the laminae , and serves for the attachment of muscles and ligaments. In animals without an erect stance, the process points upward and may slant forward or backward...

of the tail are elongate, suggesting that it swam by using a tall tail.