Belantsea

Belantsea montana (named after a legendary ancestor of the Crow Nation) was a peculiar-looking cartilaginous fish that lived during the Lower Carboniferous. Its fossils are found in the Bear Gulch Limestone lagerstätte. Its body was oddly built, being leaf-shaped, with muscular fins and a small tail.

Paleobiology
Belantsea had a bodyplan that would allow for great maneuverability, but at the cost of speedy cruising. Its few, large, triangular teeth formed a beak-like arrangement that allowed it to graze bryozoans, sponges, crinoids and other encrusting animals.

B. montana is the best known of a group of bizarre cartilaginous fish known as the "Petalodontiformes".