Sturgeons and Paddlefishes

Acipenseriformes is an order of basal ray-finned fishes that includes living and fossil sturgeons and paddlefishes (Acipenseroidei), as well as the extinct families Chondrosteidae and Peipiaosteidae. They are the second earliest diverging group of living ray-finned fish after the bichirs. Despite being early diverging, they are highly derived (modified from their ancestors), having only weakly ossified skeletons that are mostly made of cartilage, and in modern representatives highly modified skulls.