Ornithoprion

Ornithoprion is an extinct genus of cartilaginous fish. The only species, O. hertwigi, lived during the Moscovian stage of the Pennsylvanian subperiod, which spanned from . Its fossils are preserved in black shales from what is now the Midwestern United States. The study of Ornithoprion was performed primarily via x-ray imaging, and at the time of its discovery it represented one of the best known holocephalans of the Paleozoic era. The classification of the genus has been the subject of debate due to its unique anatomy, and it is now placed in the order Eugeneodontiformes and the family Caseodontidae. ''Ornithoprion's'' genus name, which may be translated from Greek as 'bird saw', was inspired by the animal's vaguely bird-like skull and the saw-like appearance of the teeth in the lower jaw, while the specific name honors German zoologist Oscar Hertwig.

Ornithoprion had a unique projection of its lower jaw termed the mandibular rostrum, which was covered by a beak of fused bony scales and which the function of in life is not known. It inhabited shallow, seasonal marine and brackish water environments, alongside a variety of other cartilaginous fishes. The rounded shape of ''Ornithoprion's teeth suggests that it hunted hard-shelled invertebrates, and bite marks and damage to some of its fossils indicate that it was in turn fed on by other carnivores. Ornithoprion was small relative to other members of its order, with a cranium length of up to and an estimated body length of up to approximately .