Choyrodon

Choyrodon
Restoration of C. barsboldi
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Sauropsida
clade:	Dinosauria
Superorder:	Ornithopodomorpha
Family:	†Iguanodontidae
Genus:	†Choyrodon Gates, 2018
Type species
†Choyrodon barsboldi Gates, 2018

Choyrodon is a genus of iguanodontid ornithopod dinosaur from the Early Cretaceous of Mongolia. It was discovered in the Khuren Dukh Formation in 2006 and named in 2018. Choyrodon was closely related to the larger Altirhinus however material has determined that both genera are separate. Instead, Choyrodon is a sister taxon to Eolambia. Material consists of a partial skull and cervical ribs in the holotype, along with two other partial skulls.

Palaeobiology

Discovery and naming

Terry Gates and his team of palaeontologists discovered a new specimen while fossil hunting in the Khuren Dukh Formation in the deserts of Mongolia. They discovered a number of remains of a sub-adult individual that belonged to some sort of unknown ornithopod. In 2018, Gates coined the name Choyrodon barsboldi. The genus name is derived from the city of Choyr and the Greek version of the word "tooth". The species name pays homage to the famous Mongolian palaeontologist Rinchen Barsbold.

Differences from Altirhinus

Choyrodon lived alongside the larger and very similar Altirhinus. They were not the same, however, and were not simply different growth stages of one another. There are a number of reasons:

Holotype skull, drawing and physical reconstruction

First, the quadratojugal notch of the quadrate is located more dorsally and lacks the dorsal prong seen on the ventral boundary of the quadratojugal notch of Altirhinus. Second, the posterior process of the postorbital of Choyrodon is steeper than that observed in Altirhinus. Third, several features observed on the palatine of Choyrodon are significantly more developed than what is observed on Altirhinus. The anterior process is exaggerated in Choyrodon, and the dorsal surface is similarly well-arched. This generally contradicts the expected pattern of exaggeration with growth observed in other dinosaurian taxa.

Fourth, overhanging on the posterior margin of the skull of Choyrodon and and the folding of the anteroventral surangular are not features linked to ontogeny. Fifth, Altithinus has a short ventral process on the predentary. Meanwhile, the feature on Choyrodon is more long and straight. Finally, Choyrodon possessed an open antorbital fenestra in the head, unlike that of Altirhinus.

Gallery