Boreosomus (meaning: "Boreal climate 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
Boreosomus belongs to the family
Ptycholepiformes (= Boreosomidae/Chungkingichthyidae). Other genera of this family are
Acrorhabdus (
Spitsbergen),
Ardoreosomus (
Nevada,
United States),
Chungkingichthys (
China),
Ptycholepis (global) and
Yuchoulepis (
China).
Some studies recover Boreosomus as a potential Chondrostei.
Description
A characteristic feature of
Boreosomus and other
Ptycholepiformes 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.
Boreosomus gillioti could reach a body length of about . Caudal fin was divided. Scales were strong and rectangular.[ 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).
Species
-
Boreosomus arcticus (Woodward, 1912) ''type species) - Early Triassic (Induan) of Svalbard
-
Boreosomus gillioti (Priem, 1924) ''Diaphorognathus - Early Triassic (Induan) of Madagascar
-
Boreosomus piveteaui Nielsen, 1942
-
Boreosomus reuterskioeldi Stensiö, 1921 - Early Triassic (Induan) of Svalbard
-
Boreosomus scaber Stensiö, 1921 - Early Triassic (Olenekian) 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.
See also
