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''Koshisaurus'' is a monospecific genus of basal
''Koshisaurus'' was unlike most hadrosauroids due to the fact that it possessed an
hadrosauroid
Hadrosauroidea is a clade or superfamily of ornithischian dinosaurs that includes the "duck-billed" dinosaurs, or hadrosaurids, and all dinosaurs more closely related to them than to ''Iguanodon''. Their remains have been recovered in Asia, Eu ...
from the Kitadani Formation
The Kitadani Formation ( ja, 北谷層 ''Kitadani-sō'') is a unit of Lower Cretaceous sedimentary rock which crops out near the city of Katsuyama in Fukui Prefecture, Japan, and it is the primary source of Cretaceous-aged non-marine vertebrate f ...
in Japan
Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...
. The discovery of the genus suggests that hadrosauroids had higher diversity along the eastern margin of Asia in the Early Cretaceous. "Koshi" means an old Japanese regional name including Fukui prefecture
is a prefecture of Japan located in the Chūbu region of Honshū. Fukui Prefecture has a population of 778,943 (1 June 2017) and has a geographic area of 4,190 km2 (1,617 sq mi). Fukui Prefecture borders Ishikawa Prefecture to the north, Gi ...
where fossils of the genus were discovered.
Description
''Koshisaurus'' was unlike most hadrosauroids due to the fact that it possessed an antorbital fossa
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 archosauriforms, first appearing during the Triassic Period. Among extant archosaurs, birds ...
, as well as three subsidiary ridges on its maxillary teeth, similar to those of '' Equijubus''. These ridges are also present on the also Asian genera '' Xuwulong'', ''Jinzhousaurus
''Jinzhousaurus'' is a genus of hadrosauroid dinosaur of the Early Cretaceous of China. The type species is ''Jinzhousaurus yangi''. The generic name refers to the town Jinzhou. The specific name honours Yang Zhongjian as the founder of Chine ...
'' and '' Altirhinus''; but all three lack antorbital fossae, placing them as more advanced than ''Koshisaurus''.,
See also
*Timeline of hadrosaur research
A timeline is a display of a list of events in chronological order. It is typically a graphic design showing a long bar labelled with dates paralleling it, and usually contemporaneous events.
Timelines can use any suitable scale represent ...
References
Hadrosaurs Fossil taxa described in 2015 Early Cretaceous dinosaurs of Asia Fossils of Japan Monotypic prehistoric reptile genera Ornithischian genera {{Ornithopod-stub