The only species, O. hertwigi, lived during the Moscovian stage of the Pennsylvanian, between 315.2 to 307 million years ago, and is known from black shale deposits in what is now the Midwestern United States.

Ornithoprion is unique among known eugeneodonts in possessing an extremely elongated structure connecting to the lower jaw, known as the mandibular rostrum, which was protected by a beak of fused bony scales and which the precise function of is not known.

The structure of Ornithoprion's teeth suggests that it was a durophage which hunted marine invertebrates, and bite marks and damage to its fossils indicate it was fed on by other carnivores.

[2] The Mecca and Logan Quarry material has been dated to the Moscovian or Desmoinesian stage of the Pennsylvanian,[3][1] which is part of the Carboniferous period and which lasted from 315.2 to 307 million years ago.

[18] American illustrator Ray Troll has proposed a total length of 60 cm (2 ft), although his reconstruction gives the species an elongated, eel-like body,[19] which is not phylogenetically supported.

The rostrum, as well as a corresponding section of the skull, was armored and reinforced by rods of bone,[18][20] which appear to have been dermal structures formed separately from the underlying cartilage or tesserae.

[7][8] The cranium is long and pointed and possesses large eye sockets, a condition which vaguely resembles the skull of a bird and inspired the name of the genus.

The palatoquadrates, which typically form the upper jaw of living cartilaginous fish, are reduced and immobile, and articulate with the cranium in a greatly limited, autodiastylic (two jointed) manner.

[2][18][24] This unpaired intercoracoidal cartilage has also been identified in living broadnose sevengill sharks,[25] as well as the extinct iniopterygians, the Jurassic chimaeriform Ischyodus,[24] and potentially the closely related Fadenia.

If Zangerl's interpretation of the dermal structures of O. hertwigi is correct, it would represent a rare example of bone among extinct euchondrocephalans, which otherwise have denticles and armor composed of dentin.

[2] In his original 1966 description, Zangerl speculates that the reinforcing "beak" of bony rods present on the snout and rostrum were formed by the compounding of these polydontode scales.

[18] In 1981, Zangerl considered O. hertwigi as a member of Caseodontidae, as part of the larger superfamily Caseodontoidea and the newly established order Eugeneodontida, in light of the numerous new taxa and characteristics that had been observed since Ornithoprion's original description.

[2] Its classification within the Caseodontidae is based on the bulbous, rounded nature of its tooth crowns and reduction of its palatoquadrates, features which are also found in related genera such as Caseodus.

[7]Fadenia Erikodus Ornithoprion Caseodus Romerodus Bobbodus Eugeneodus Gilliodus Campyloprion Parahelicoprion Helicoprion Agassizodus Toxoprion Sarcoprion Syntomodus Lestrodus Edestus Helicampodus Parahelicampodus The Mecca, Logan, and Excello shales all represent marine depositional environments, and all preserve a diverse assemblage of species.

[34][9][35] In a 1963 publication, researchers Rainer Zangerl and Eugene Richardson proposed that the Mecca and Logan sites were extremely shallow habitats, likely less than a meter (3.3 ft) of water, with small, isolated deeper areas.

[36] The presence of peat and coal indicates that the deposits overlay drowned forests and are a recent transgression of a marine environment over a terrestrial one (known as a cyclothem).

[9] The Logan and Mecca environment likely only existed for a brief period, with overlying invertebrate communities and limestone deposits indicating that deeper water eventually flooded the region and created a more stable habitat.

[21] Invertebrates such as brachiopods and ammonoids are known from the Excello Shale, as are a wide variety of cartilaginous fishes including Listracanthus, Caseodus, Edestus, and Stethacanthus, all of which were roughly contemporaneous with Ornithoprion.

[2] In a 2019 publication, author Wayne Itano suggests that the bisected fish remains of the Mecca and Logan shales, such as the known fossils of O. hertwigi, may be the result of a novel feeding method displayed by the contemporaneous and much larger Edestus, which cut prey in half in a manner similar to modern sawfish.

The rounded, bulbous crowns of the lower symphyseal whorl appear to be an adaptation for crushing,[2][19] and the remains of brachiopod shells are known from the stomach of the related Fadenia.

[21] Some features of the animal's skull, such as the armor and articulation of the upper and lower jaws, are suggested by Zangerl to be shock-absorbing adaptations, although he considers it unlikely that the rostrum was used as a weapon.

Ray Troll, an Alaskan illustrator, has cited the taxon as one of his references while reconstructing the potential close relative and more widely publicized genus Helicoprion.

[14]: 144, 151  Both murals and a life-sized model of Helicoprion davidsii, designed by Troll and displayed at the Idaho Museum of Natural History,[43] directly reference features of O. hertwigi such as gill anatomy.

Edestid researcher Bendix-Almgreen had, however, criticized the use of caseodonts as the basis for Helicoprion in Troll's art, as he believed they did not represent close phylogenetic or ecological analogues.