Tchoiria 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 simoedosaurid 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 crocodile

Crocodile

A crocodile is any species belonging to the family Crocodylidae . The term can also be used more loosely to include all extant members of the order Crocodilia: i.e...

-like aquatic reptile. Fossils of this genus have been found in Early Cretaceous

Early Cretaceous

The Early Cretaceous or the Lower Cretaceous , is the earlier or lower of the two major divisions of the Cretaceous...

-age rocks in Mongolia. Four species have been named, but two have been given their own genera. 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...

 is T. namsari, based on

Holotype

A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...

 PIN 3386/1, a partial skull and skeleton 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...

. Two other species were named from this locality, with both later being reassigned: T. egloni, now Irenosaurus egloni

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 T. magnus, now Ikechosaurus magnus

Ikechosaurus

Ikechosaurus is an extinct genus of choristoderan which existed in China and Mongolia during the Cretaceous period. It contains the species Ikechosaurus sunailinae and Ikechosaurus gaoi....

. A fourth species, T. klauseni, was named from a partial skull and skeleton found in rocks of roughly the same age farther west in Mongolia.