Boreosomus

{{Automatic taxobox

| name = Boreosomus

| fossil_range = {{fossilrange|252|237|Early Triassic to Middle Triassic}}

| image = Boreosomus gillioti Priem.jpg|

| image_caption = Boreosomus gillioti: fossil mold and latex cast

| taxon = Boreosomus

| authority = Stensiö, 1921

| synonyms = *Diaphorognathus Brough, 1933

| type_species = †Acrolepis arctica

| type_species_authority = Woodward, 1912

}}

Boreosomus (meaning: "boreal body") is an extinct genus of Triassic marine ray-finned fish. It was first described from the Arctic island of Spitsbergen (Svalbard, Norway), hence its genus name, but was later also discovered in other parts of the world. The type species is Boreosomus arcticus (= Acrolepis arctica Woodward, 1912).

Classification

File: Ptycholepidae - Boreosomus gillioti.JPG

File: Boreosomus.jpg ]]

Boreosomus belongs to the family Ptycholepidae (= Boreosomidae/Chungkingichthyidae). Other genera of this family are Acrorhabdus (Spitsbergen), Ardoreosomus (Nevada, United States), Chungkingichthys (China), Ptycholepis (global) and Yuchoulepis (China).{{cite journal |last1=Romano |first1=Carlo |last2=López-Arbarello |first2=Adriana |last3=Ware |first3=David |last4=Jenks |first4=James F. |last5=Brinkmann |first5=Winand |year=2019 |title=Marine Early Triassic Actinopterygii from the Candelaria Hills (Esmeralda County, Nevada, USA) |journal=Journal of Paleontology |volume=93 |issue=5 |pages=971–1000 |doi=10.1017/jpa.2019.18|bibcode=2019JPal...93..971R |s2cid=155564297 }}

Some studies recover Boreosomus as a potential chondrostean.{{cite journal |last1=Near |first1=Thomas J |last2=Thacker |first2=Christine E |date=18 April 2024 |title=Phylogenetic classification of living and fossil ray-finned fishes (Actinopterygii) |journal=Bulletin of the Peabody Museum of Natural History |volume=65 |doi=10.3374/014.065.0101 |doi-access=free|url=https://zenodo.org/records/8352027/files/Near%26Thacker_preprint.pdf }}

Description

A characteristic feature of Boreosomus and other ptycholepids is the dorsal fin, which inserts at the level of the pelvic fins in the middle portion of the body. Most contemporary ray-fins have their dorsal fin in a more posterior position, often opposite to the anal fin. Also typical for ptycholepids are the somewhat rectangular, horizontally arranged suborbital bones.{{cite journal |last=Nielsen |first=Eigil |author-link=Eigil Nielsen (paleontologist) |year=1942 |title=Studies on Triassic fishes from East Greenland 1. Glaucolepis and Boreosomus |journal=Palaeozoologica Groenlandica |volume=1 |pages=1–403}}

Boreosomus gillioti could reach a body length of about {{cvt|10|-|20|cm}}. Caudal fin was divided. Scales were strong and rectangular.[http://www.thefossilforum.com/index.php?/collections-database/chordata/fishes/boreosomus-gillioti-priem-1924-r171/ The Fossil Forum]

Fossil record

Boreosomus had a worldwide distribution during the Early Triassic and is also known from the Middle Triassic. Fossils of Boreosomus were found, apart from Spitsbergen (Svalbard), in Greenland, Madagascar, China (Shaanxi), Spain (Catalonia), United States (Arizona), and Canada (British Columbia).{{Cite web |title=PBDB |url=https://paleobiodb.org/classic/basicTaxonInfo?taxon_no=34976 |access-date=2024-04-01 |website=paleobiodb.org}}{{cite journal |last1=Romano |first1=Carlo |last2=Koot |first2=Martha B. |last3=Kogan |first3=Ilja |last4=Brayard |first4=Arnaud |last5=Minikh |first5=Alla V. |last6=Brinkmann |first6=Winand |last7=Bucher |first7=Hugo |last8=Kriwet |first8=Jürgen |title=Permian-Triassic Osteichthyes (bony fishes): diversity dynamics and body size evolution |journal=Biological Reviews |date=2016 |volume=91 |issue=1 |pages=106–147 |doi=10.1111/brv.12161 |pmid=25431138 |s2cid=5332637|url=https://hal.science/hal-01253154/file/Romano_et_al_HAL.pdf }}

Species

{{extinct}}Boreosomus arcticus (Woodward, 1912) [Acrolepis arctica Woodward 1912] (type species) - Early Triassic (Induan) of Svalbard
{{extinct}}Boreosomus gillioti (Priem, 1924) [Diaphorognathus gillioti (Priem 1924); Gyrolepis gillioti Priem 1924] - Early Triassic (Induan) of Madagascar
{{extinct}}Boreosomus piveteaui Nielsen, 1942 - Earliest Triassic (Induan) of Greenland
{{extinct}}Boreosomus reuterskioeldi Stensiö, 1921 - Early Triassic (Induan) of Svalbard
{{extinct}}Boreosomus scaber Stensiö, 1921 - Early Triassic (Spathian) of Svalbard

Indeterminate species are known from the Early Triassic of Canada (British Columbia) and China (Guizhou), as well as the Middle Triassic of Svalbard, Spain, and possibly the United States (Arizona).

The species B. merlei is now placed in Australosomus.{{Cite journal |last=Brinkmann |first=W. |last2=Romano |first2=C. |last3=Bucher |first3=H. |last4=Ware |first4=D. |last5=Jenks |first5=J. |date=2010 |title=Palaeobiogeography and stratigraphy of advanced Gnathostomian fishes (Chondrichthyes and Osteichthyes) in the Early Triassic and from selected Anisian localities (report 1863-2009): Literaturbericht |url=http://www.schweizerbart.de/series/zgp2 |journal=Zentralblatt für Geologie und Paläontologie, Teil II |volume=2009 |issue=5/6 |pages=765–812 |doi=10.5167/uzh-34071 |issn=0044-4189}}