Semionotiformes is an order of ray-finned fish known from the Middle
Triassic (
Anisian)[1] to the Late
Cretaceous (
Maastrichtian).[2] Their closest living relatives are
gars (Lepisosteidae), with both groups belonging to the clade
Ginglymodi within the
Holostei.[1] The group includes both freshwater (Semionotidae) and marine (Callipurbeckiidae,
Macrosemiidae) adapted forms.[3] Many members of the family Macrosemiidae (which are usually included in Semionotiformes but sometimes placed in their own order), had elongated dorsal fins, often associated with an adjacent area of skin which was free of scales. These fins were likely undulated for use in precision swimming. The body morphology of macrosemiids suggests that they were slow swimmers that were capable of maneuvering around complex topography, such as reef environments.[4]
Classification
Order †Semionotiformes Arambourg & Bertin 1958 sensu López-Arbarello 2012[5][6][7][8]