''Khurendukhosaurus'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

choristodere Choristodera (from the Greek χωριστός ''chōristos'' + δέρη ''dérē'', 'separated neck') is an extinct order of semiaquatic diapsid reptiles that ranged from the Middle Jurassic, or possibly Triassic, to the late Miocene (168 to ...

, a type of amphibious reptile. It is known from

Lower Cretaceous Lower may refer to: *Lower (surname) *Lower Township, New Jersey *Lower Receiver (firearms) *Lower Wick Lower Wick is a small hamlet located in the county of Gloucestershire, England. It is situated about five miles south west of Dursley, eight ...

rocks of

Mongolia Mongolia; Mongolian script: , , ; lit. "Mongol Nation" or "State of Mongolia" () is a landlocked country in East Asia, bordered by Russia to the north and China to the south. It covers an area of , with a population of just 3.3 million, ...

and

Russia Russia (, , ), or the Russian Federation, is a List of transcontinental countries, transcontinental country spanning Eastern Europe and North Asia, Northern Asia. It is the List of countries and dependencies by area, largest country in the ...

. Two species have been named. The

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen ...

, ''K. orlovi'', was named in 1984 by Sigogneau–Russell and Efimov for the fragmentary

postcrania Postcrania (postcranium, adjective: postcranial) in zoology and vertebrate paleontology is all or part of the skeleton apart from the skull. Frequently, fossil remains, e.g. of dinosaurs or other extinct tetrapods, consist of partial or isolated sk ...

l skeleton

PIN A pin is a device used for fastening objects or material together. Pin or PIN may also refer to: Computers and technology * Personal identification number (PIN), to access a secured system ** PIN pad, a PIN entry device * PIN, a former Dutch de ...

3386/3. This specimen was discovered in the

Albian The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous Epoch/Series. Its approximate time range is 113.0 ± 1.0 Ma to 100.5 ± 0.9 M ...

-age

Khuren Dukh Formation The Khuren Dukh Formation, also known as the Hühteeg Svita, ( mn, Хөхтээг формаци, ) is a geological formation in Mongolia whose strata date back to the middle to late Albian.Nichols et al., 2006 Dinosaur remains are among the fossil ...

Formation at Hüren Dukh, central

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

Irenosaurus ''Irenosaurus'' is a genus of choristodere, a type of amphibious reptile. It is known from a single fragmentary postcranial skeleton (PIN 3386/2), discovered in the Aptian-age Lower Cretaceous Hühteeg Formation at Hüren Dukh, central Mo ...

'' and ''

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 ...

''. 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 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 ''shoulde ...

and a rib. These bones were found in the

Murtoi Formation at

Lake Gusinoye Lake Gusinoye (russian: Гусиное озеро, ''Gusinoye ozero''; mn, Галуут нуур, Galuut nuur) is the name of a body of fresh water in the Republic of Buryatia, Russia. Geography The lake is located in the Gusinoozyor Basin betwe ...

Buryatia Buryatia, officially the Republic of Buryatia (russian: Республика Бурятия, r=Respublika Buryatiya, p=rʲɪsˈpublʲɪkə bʊˈrʲætʲɪjə; bua, Буряад Улас, Buryaad Ulas, , mn, Буриад Улс, Buriad Uls), is ...

. 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 Doubt is a mental state in which the mind remains suspended between two or more contradictory propositions, unable to be certain of any of them. Doubt on an emotional level is indecision between belief and disbelief. It may involve uncertainty, ...

within the genus. An indeterminate species is known from the

Batylykh Formation The Batylykh Formation is a geological formation in Yakutia, Russia. It is of an uncertain Early Cretaceous age, probably dating between the Berriasian and the Barremian. It is the oldest unit of the thick Sangar Series within the Vilyuy syne ...

. ''Khurendukhosaurus'' was a small choristodere, approximately long at most. Efimov and Storrs regarded it as a basal member of Choristodera, but Skutschas was unable to confirm this in a

phylogenetic analysis In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

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

neural spines The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...

of the tail are elongate, suggesting that it swam by using a tall tail. In 2019, another partial skeleton (MPC-MX 1/107) of the taxon was described from the Khuren Dukh Formation, confirming the presence of a long neck with at least 13 cervical vertebrae. A phylogenetic analysis found it to be the most basal hyphalosaurid. Phylogeny from the analysis of Dong and colleagues (2020):

References

{{Taxonbar, from=Q6403075 Choristodera Cretaceous choristoderes Early Cretaceous reptiles of Asia Prehistoric reptile genera