''Choyrodon'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

hadrosauroid Hadrosauroidea is a clade or superfamily of ornithischian dinosaurs that includes the "duck-billed" dinosaurs, or Hadrosauridae, and all dinosaurs more closely related to them than to ''Iguanodon''. Their remains have been recovered in Asia, Euro ...

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...

from the

Early Cretaceous The Early Cretaceous (geochronology, geochronological name) or the Lower Cretaceous (chronostratigraphy, chronostratigraphic name) is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 143.1 ...

Albian The Albian is both an age (geology), age of the geologic timescale and a stage (stratigraphy), stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early Cretaceous, Early/Lower Cretaceous epoch (geology), Epoch/s ...

-age

Khuren Dukh Formation The Khuren Dukh Formation, also known as the Khukhtyk Formation, Khukhteeg Formation, or Hühteeg Svita, (, ), is a geological formation in Mongolia whose strata date back to the Aptian–Albian ages of the Early Cretaceous.Nichols et al., 2006 D ...

Mongolia Mongolia is a landlocked country in East Asia, bordered by Russia to the north and China to the south and southeast. It covers an area of , with a population of 3.5 million, making it the world's List of countries and dependencies by po ...

. The

type Type may refer to: Science and technology Computing * Typing, producing text via a keyboard, typewriter, etc. * Data type, collection of values used for computations. * File type * TYPE (DOS command), a command to display contents of a file. * ...

and only species is ''Choyrodon barsboldi''. The generic name is derived from the city of Choyr, and ''-odon'', from

Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

for tooth; the specific name ''barsboldi'' honours

paleontologist Paleontology, also spelled as palaeontology or palæontology, is the scientific study of the life of the past, mainly but not exclusively through the study of fossils. Paleontologists use fossils as a means to classify organisms, measure geolo ...

Rinchen Barsbold Rinchen Barsbold (, Rinchyengiin Barsbold, born December 21, 1935, in Ulaanbaatar) is a Mongolian paleontologist and geologist. He works with the Institute of Geology, at Ulaanbaatar, Mongolia. He is an expert in vertebrate paleontology and Mesozo ...

. The material consists of a

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

partial skull and cervical ribs, with two other partial skulls both with associated postcranial material. It was found to be the

sister taxon In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...

of ''

Eolambia ''Eolambia'' (meaning "dawn lambeosaurine") is a genus of herbivorous hadrosauroid dinosaur from the early Late Cretaceous of the United States. It contains a single species, ''E. caroljonesa'', named by paleontologist James Kirkland in 19 ...

''.

History and naming

Three specimens of a new

iguanodontia Ornithopoda () is a clade of ornithischian dinosaurs, called ornithopods (). They represent one of the most successful groups of herbivorous dinosaurs during the Cretaceous. The most primitive members of the group were bipedal and relatively sm ...

n were discovered in the

by an expedition led by Mongolian paleontologist

. These three specimens, stored in the

Mongolian Natural History Museum The Natural History Museum () is a repository and research institution located in Chingeltei, Ulaanbaatar, Mongolia. The museum was previously known as the Mongolian National Museum or State Central Museum. The museum includes Departments of Geo ...

, were found within the same sediments that had yielded the iguanodontian ''

Altirhinus ''Altirhinus'' (; "high nose") is a genus of hadrosauroid ornithopod dinosaur from the Early Cretaceous period of Mongolia. History of discovery All known specimens of ''Altirhinus'' were recovered in 1981 during collaborative expeditions organ ...

'', but comparisons showed that they represented different taxa and so in

2018 Events January * January 1 – Bulgaria takes over the Presidency of the Council of the European Union, after the Estonian presidency. * January 4 – SPLM-IO rebels loyal to Chan Garang Lual start a raid against Juba, capital of ...

American paleontologist Terry Gates and colleagues named them ''Choyrodon barsboldi''. The genus name is derived from the nearby city of Choyr and the

word for "tooth", ''don'', while the species name is in honour of Barsbold and his contributions to Mongolian paleontology. Three specimens of ''Choyrodon'' are known, each from a different locality of the lower member of the Khuren Dukh Formation. The

is MPC-D 100/801, and includes a partial but mostly complete disarticulated skull, while the referred specimens, MPC-D 100/800 and MPC-D 100/803, preserve another partial skull and fragmentary skeleton, and a fragmentary skull and partial skeleton, respectively. The quarry the holotype was found in is a thick brown-black

siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility. Although its permeabil ...

at the Khuren Dukh locality of the formation, with an age of approximately middle to late

based on

palynology Palynology is the study of microorganisms and microscopic fragments of mega-organisms that are composed of acid-resistant organic material and occur in sediments, sedimentary rocks, and even some metasedimentary rocks. Palynomorphs are the mic ...

Classification

Gates and colleagues assessed the position of ''Choyrodon''

phylogenetically In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical data ...

when describing the taxon, under two varying conditions. ''Choyrodon'' displays an open

antorbital fenestra An antorbital fenestra (plural: fenestrae) is an opening in the skull that is in front of the eye sockets. This skull character is largely associated with Archosauriformes, archosauriforms, first appearing during the Triassic Period. Among Extant ...

, which clearly distinguishes it from coexisting ''Altirhinus'', but this feature can vary during growth so they assessed the impact of treating the fenestra as present or absent in an adult would alter relationships. They found that the presence or absence of an antorbital fenestra in adults did not significantly change the relationships of ''Choyrodon'', with it either as the sister taxon of ''

'' or an intermediate early

. There was not support for interpreting ''Choyrodon'' as a juvenile ''Altirhinus'', despite their similar anatomy, age, and location.

References

{{Taxonbar, from=Q55949103 Hadrosauroidea Dinosaur genera Albian dinosaurs Taxa named by Lindsay Zanno Fossil taxa described in 2018 Dinosaurs of Mongolia