Amakusaichthys

Amakusaichthys Temporal range: Santonian–Campanian PreꞒ Ꞓ O S D C P T J K Pg N
Skull of A. gosyouraensis
Type specimen of A. benammii
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	† Ichthyodectiformes
Family:	† Heckelichthyidae
Genus:	† Amakusaichthys Yabumoto et al. 2018
Type species
†Amakusaichthys goshouraensis Yabumoto et al. 2018
Other species
†A. benammiiAlvarado-Ortega, 2024

Amakusaichthys is an extinct genus of ichthyodectiform ray-finned fish which lived during the Late Cretaceous, known from two species A. goshouraensis from Kumamoto Prefecture in Japan ^[1] and A. benammii from Chiapas in Mexico. ^[2]

Discovery

Fossils of A. goshouraensis were discovered in 2012 from construction site in Goshoura, Amakusa. ^[3] This site is later considered to belong to Hinoshima Formation of the Himenoura Group. ^[1] It was the first discovery of marine ichthyodectform fish described from Asia in detail, while other ichthyodectiform fish from Asia (three genera belong to Chuhsiungichthyidae) are from non-marine environment. ^{[1] [3]}

Second species, A. benammii is described from Angostura Formation in Tzimol Quarry, Chiapas, southeastern Mexico. ^[2]

Description

Life restoration of A. goshouraensis

Amakusaichthys is relatively small ichthyodectiform with length around 60 cm (24 in). It is characterized by its long snout and small mouth and teeth. ^[1] Multiple specimens are found overlapped in one place, suggesting its schooling ecology. ^{[3] [4]}

Classification

Amakusaichthys was not assigned to any family in original description. However, characters suggested that it was related to Heckelichthys . ^[1] In 2021, it was assigned to Bardackichthyidae, alongside Heckelichthys and Bardackichthys . ^[5] However, a 2024 paper which described a new species A. benammii placed both Amakusaichthys and Heckelichthys (with Garganoichthys and Altamuraichthys as other probable members) into a separate family Heckelichthyidae, and questioned the inclusion of Bardackichthys and Chuhsiungichthyidae within Ichthyodectiformes. ^[2]

References

1. Yabumoto, Yoshitaka; Hirose, Koji; Brito, Paulo M. (2020-03-15). "A new ichthyodectiform fish, Amakusaichthys goshouraensis gen. et sp. nov. from the Upper Cretaceous (Santonian) Himenoura Group in Goshoura, Amakusa, Kumamoto, Japan". Historical Biology. 32 (3): 362–375. doi:10.1080/08912963.2018.1497022. ISSN   0891-2963. S2CID   91632554.
2. Alvarado-Ortega, Jesús (2024-12-29). "Amakusaichthys benammii sp. nov., a Campanian long-nose ichthyodectiform fish from the Tzimol Quarry, Chiapas, southeastern Mexico". Palaeontologia Electronica. 27 (3): 1–37. doi: 10.26879/1444 . ISSN   1094-8074.
3. "天草市御所浦町で発見された白亜紀の新属新種の大型魚類化石 - 天草市立御所浦白亜紀資料館". gcmuseum.ec-net.jp. Retrieved 2022-11-09.
4. 浩司, 廣瀬; 美孝, 籔本; M, ブリトー パウロ (2019). "熊本県天草市御所浦町に分布する上部白亜系姫浦層群から発見されたイクチオデクテス目魚類Amakusaichthys goshouraensisアマクサゴショウラムカシウオ(新称)". 化石. 105: 1–2. doi:10.14825/kaseki.105.0_1.
5. Hacker, Riley J.; Shimada, Kenshu (2021-07-01). "A new ichthyodectiform fish (Actinopterygii: Teleostei) from the Arlington Member (mid-Cenomanian) of the Upper Cretaceous Woodbine Formation in Texas, USA". Cretaceous Research. 123: 104798. doi:10.1016/j.cretres.2021.104798. ISSN   0195-6671. S2CID   233806833.