What is "petalodontiformes"

Petalodontiformes ("thin-plate teeth") is an extinct order of marine cartilaginous fish related to modern day chimaera found in what is now the United States of America and Europe. With a very few exceptions, they are known entirely from teeth. All fossils range from the Carboniferous to the Permian, where they are presumed to have died out during the Permian/Triassic extinction event.

The two best known species are Belantsea montana, of Carboniferous Bear Gulch, Montana, and Janassa bituminosa, of Permian Europe, as whole fossil specimens have been found of these two.