''Aokiichthys'' is an extinct genus of basal osteoglossoid from an Early

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...

freshwater palaeolake of what is now

Kyushu is the third-largest island of Japan's five main islands and the most southerly of the four largest islands ( i.e. excluding Okinawa). In the past, it has been known as , and . The historical regional name referred to Kyushu and its surroun ...

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 genus formed a species radiation in the First Formation within the Wakino Subgroup of the Kwanmon Group, as a dominant member and namesake of the '' Nipponamia''-''Aokiichthys'' fauna. The genus became extinct at the end of either the 1st Formation, or possibly during the 2nd Formation, when the palaeolake became shallower. ''Aokiichthys'' is described as being closely related to the genera '' Yungkangichthys'', and ''

Paralycoptera ''Paralycoptera wui'' is an extinct species of basal osteoglossoid from Early Cretaceous freshwater environments of what is now China. ''P. wui'' was originally described as a lycopterid osteoglossomorph close to ''Lycoptera'', though, later ...

'' (at the time of ''Aokiichthys description, all three genera were thought to be lycopterids). In their 2009 study, Xu and Chang reassess ''Paralycoptera'' to be a basal osteoglossoid, and synonymized both ''Yungkangichthys'' and ''Aokiichthys'' into ''Paralycoptera''.

Etymology

The generic name honors one (Mr. Tateyu) Aoki, who collected and donated the majority of the first specimens.

Species

''A. toriyamai''

''A. toriyamai'' is the type species of the genus. It has a comparatively moderate body. Body lengths range from about 35 to 75 millimeters. The specific name honors the late Dr. Ryuzu Toriyama, who was the lead advisor on the first two expeditions for Mesozoic fossils in

Kitakyushu City is a Cities of Japan, city located in Fukuoka Prefecture, Japan. As of June 1, 2019, Kitakyushu has an estimated population of 940,978, making it the second-largest city in both Fukuoka Prefecture and the island of Kyushu after the city of Fuku ...

''A. changae''

''A. changae'' has large teeth on its

parasphenoid The parasphenoid is a bone which can be found in the cranium of many vertebrates. It is an unpaired dermal bone which lies at the midline of the roof of the mouth. In many reptiles (including birds), it fuses to the endochondral (cartilage-derived) ...

. It has a comparatively moderate body. Body lengths range from about 63 to 83 millimeters. The specific name honors the Chinese palaeoichthyologist, Dr. Chang Mee-Mann, one of the leading experts in Chinese Mesozoic fish fossils.

''A. otai''

''A. otai'' is a very deep-bodied species that closely resembles ''Yungkangichthys''. Body lengths range from 55 to 60 millimeters. The specific name honors Dr. Masamichi Ota, who organized the first expedition for Mesozoic fossils in Kitakyushu City.

''A. uyenoi''

''A. uyenoi'' is a fairly deep-bodied species. The average body length is around 56 millimeters. The specific name honors the Japanese ichthyologist, Dr. Teruya Uyeno, who advised Yoshitaka Yabumoto in his description of the Wakino Subgroup fish taxa.

''A. praedorsalis''

''A. praedorsalis'' is the largest species in the genus, with a typical length of 147 millimeters. The specific name refers to how the large dorsal fin is placed more anteriorly in comparison to the other species.

References

Osteoglossiformes Prehistoric ray-finned fish genera Cretaceous bony fish Early Cretaceous fish of Asia Fossils of Japan Freshwater fish Fossil taxa described in 1994 {{paleo-rayfinned-fish-stub