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Ornithoprion
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Ornithoprion
Ornithoprion is an extinct genus of cartilaginous fish. The only species, O. hertwigi, lived during the Moscovian stage of the Pennsylvanian, which spanned from 315 to 307 million years ago. 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 Paleozoic holocephalans. The classification of the genus has been the subject of debate due to its unique anatomy, but 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 species name honors German zoologist Oscar Hertwig.
Ornithoprion is unique among known eugeneodonts for the extremely long mandibular rostrum extending from the lower jaw, which was covered by a beak of fused bony scales and which the function of in life is not known. It inhabited shallow marine environments and coexisted with a variety of other cartilaginous fishes. The structure of Ornithoprion's teeth suggests that it hunted hard-shelled invertebrates, and bite marks and damage to its fossils indicate it was fed on by other carnivores. Ornithoprion was small relative to other members of its order, with a cranium length of up to 10 centimetres (3.9 in) and an estimated body length of up to approximately 91 centimetres (36 in).
Ornithoprion hertwigi was named and described in 1966 by paleontologist Rainer Zangerl in a paper published by the Field Museum of Natural History (then the Chicago Museum of Natural History). This description was based on material collected primarily from the Mecca Quarry of Parke County, Indiana, in rocks which are part of the Linton Formation. A single specimen was also described from the Logan Quarry in an exposure of the Staunton Formation, also in Parke County, and another from near Wilmington, Illinois that is part of a private collection. The specimens are all preserved in carbonaceous black shale, and the preservation mode of the Illinois specimen has been described as pyritic. The Mecca and Logan Quarry material has been dated to the Moscovian stage of the Pennsylvanian subperiod, which itself is part of the Carboniferous period and which spanned from 315 to 307 million years ago. The precise age and locality of the Illinois specimen is unknown. Nine specimens of Ornithoprion were initially described, with specimen FMNH PF-2710 from the Mecca Quarry being designated as the holotype (defining specimen of the taxon). Additional material has subsequently been assigned to the genus, including occurrences from the Excello Shale of Indiana.
Like many other fish fossils from the Mecca and Logan quarries, the studies of the holotype and paratypes of Ornithoprion were primarily performed by radiographic imaging. The specimens, which are extremely delicate, were not extracted from the surrounding rock matrix and were instead scanned via stereoscopic X-rays to study the hard parts of the body from within the shale. The Staunton Formation specimen, FMNH PF-2656, was also cut into multiple cross-sections, which allowed for study of the internal anatomy of the scales and teeth. At the time of its discovery Ornithoprion was one of the few members of its order known from postcranial fossils, alongside Fadenia, Erikodus, and what would later be described as Eugeneodus. It also represented one of only a small number of holocephalans from the Paleozoic in which the endoskeleton was known, and alongside the related Fadenia was the only one known to preserve the gills.
The genus name, Ornithoprion, translates literally from Greek as 'bird saw' and is in reference to the saw-like row of teeth in the lower jaw and the animal's pointed, beaked skull. The species name, O. hertwigi, honors German zoologist Oscar Hertwig.
Ornithoprion is known from multiple articulated but incomplete specimens, with none preserving skeletal material beyond the pectoral girdle. Most of these specimens are preserved in lateral view, and all, including the holotype, are flattened. The preserved portion of the skeleton was composed of cartilage reinforced by an outer coating of mineralized tesserae; hexagonal structures which strengthen the cartilage and are also present in the skeletons of other cartilaginous fish. While the postcranial anatomy of Ornithoprion is incompletely known, other members of the family Caseodontidae are characterized by a streamlined body, a homocercal (crescent-shaped) caudal fin, and reduced or absent pelvic fins. Zangerl described O. hertwigi as "very small" in his description of the taxon, and author Richard Ellis suggested a total length of 90 cm (3 ft) based on an assumed skull length of less than 15 cm (6 in) in a 2003 book.
The lower jaw of Ornithoprion was roughly 1.3 times the length of the rest of the skull, and had a forward-facing projection termed the mandibular rostrum. While similar rostra are known in other eugeneodonts, the structure was significantly longer in Ornithoprion, and both the rostrum and a correlating section of the snout were uniquely armored by rods of bone embedded in the skin. In life, the mandibular rostrum was likely to have been cylindrical in cross section and spear-like, with the exception of the rear portion which had a bulge that supported the teeth. There is no indication that the mandibular rostrum contained sensory organs. The rostrum articulated with the Meckel's cartilages (equivalent to the mandible), and a flattened keel of cartilage protruded from the bottom of the rostrum near this point of contact. The Meckel's cartilages themselves consisted of a pair of thin, flattened cartilages which articulated with the palatoquadrates.
The palatoquadrates, which typically form the upper jaws in living cartilaginous fish, were reduced, immobile, and potentially fused partially with the cranium. This reduced state is unique among cartilaginous fish, and differs greatly from that seen in other eugeneodonts such as Helicoprion, in which the palatoquadrates were large and specialized, and potentially Fadenia and Sarcoprion, which may have had them entirely fused to the cranium (termed holostyly) or completely lost. The condition in O. hertwigi most closely resembled that of other caseodonts such as Caseodus and Eugeneodus, although the degree of reduction is much greater in Ornithoprion. The palatoquadrate articulated at the back of the neurocranium in a greatly limited, modified two jointed manner.
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Ornithoprion
Ornithoprion is an extinct genus of cartilaginous fish. The only species, O. hertwigi, lived during the Moscovian stage of the Pennsylvanian, which spanned from 315 to 307 million years ago. 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 Paleozoic holocephalans. The classification of the genus has been the subject of debate due to its unique anatomy, but 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 species name honors German zoologist Oscar Hertwig.
Ornithoprion is unique among known eugeneodonts for the extremely long mandibular rostrum extending from the lower jaw, which was covered by a beak of fused bony scales and which the function of in life is not known. It inhabited shallow marine environments and coexisted with a variety of other cartilaginous fishes. The structure of Ornithoprion's teeth suggests that it hunted hard-shelled invertebrates, and bite marks and damage to its fossils indicate it was fed on by other carnivores. Ornithoprion was small relative to other members of its order, with a cranium length of up to 10 centimetres (3.9 in) and an estimated body length of up to approximately 91 centimetres (36 in).
Ornithoprion hertwigi was named and described in 1966 by paleontologist Rainer Zangerl in a paper published by the Field Museum of Natural History (then the Chicago Museum of Natural History). This description was based on material collected primarily from the Mecca Quarry of Parke County, Indiana, in rocks which are part of the Linton Formation. A single specimen was also described from the Logan Quarry in an exposure of the Staunton Formation, also in Parke County, and another from near Wilmington, Illinois that is part of a private collection. The specimens are all preserved in carbonaceous black shale, and the preservation mode of the Illinois specimen has been described as pyritic. The Mecca and Logan Quarry material has been dated to the Moscovian stage of the Pennsylvanian subperiod, which itself is part of the Carboniferous period and which spanned from 315 to 307 million years ago. The precise age and locality of the Illinois specimen is unknown. Nine specimens of Ornithoprion were initially described, with specimen FMNH PF-2710 from the Mecca Quarry being designated as the holotype (defining specimen of the taxon). Additional material has subsequently been assigned to the genus, including occurrences from the Excello Shale of Indiana.
Like many other fish fossils from the Mecca and Logan quarries, the studies of the holotype and paratypes of Ornithoprion were primarily performed by radiographic imaging. The specimens, which are extremely delicate, were not extracted from the surrounding rock matrix and were instead scanned via stereoscopic X-rays to study the hard parts of the body from within the shale. The Staunton Formation specimen, FMNH PF-2656, was also cut into multiple cross-sections, which allowed for study of the internal anatomy of the scales and teeth. At the time of its discovery Ornithoprion was one of the few members of its order known from postcranial fossils, alongside Fadenia, Erikodus, and what would later be described as Eugeneodus. It also represented one of only a small number of holocephalans from the Paleozoic in which the endoskeleton was known, and alongside the related Fadenia was the only one known to preserve the gills.
The genus name, Ornithoprion, translates literally from Greek as 'bird saw' and is in reference to the saw-like row of teeth in the lower jaw and the animal's pointed, beaked skull. The species name, O. hertwigi, honors German zoologist Oscar Hertwig.
Ornithoprion is known from multiple articulated but incomplete specimens, with none preserving skeletal material beyond the pectoral girdle. Most of these specimens are preserved in lateral view, and all, including the holotype, are flattened. The preserved portion of the skeleton was composed of cartilage reinforced by an outer coating of mineralized tesserae; hexagonal structures which strengthen the cartilage and are also present in the skeletons of other cartilaginous fish. While the postcranial anatomy of Ornithoprion is incompletely known, other members of the family Caseodontidae are characterized by a streamlined body, a homocercal (crescent-shaped) caudal fin, and reduced or absent pelvic fins. Zangerl described O. hertwigi as "very small" in his description of the taxon, and author Richard Ellis suggested a total length of 90 cm (3 ft) based on an assumed skull length of less than 15 cm (6 in) in a 2003 book.
The lower jaw of Ornithoprion was roughly 1.3 times the length of the rest of the skull, and had a forward-facing projection termed the mandibular rostrum. While similar rostra are known in other eugeneodonts, the structure was significantly longer in Ornithoprion, and both the rostrum and a correlating section of the snout were uniquely armored by rods of bone embedded in the skin. In life, the mandibular rostrum was likely to have been cylindrical in cross section and spear-like, with the exception of the rear portion which had a bulge that supported the teeth. There is no indication that the mandibular rostrum contained sensory organs. The rostrum articulated with the Meckel's cartilages (equivalent to the mandible), and a flattened keel of cartilage protruded from the bottom of the rostrum near this point of contact. The Meckel's cartilages themselves consisted of a pair of thin, flattened cartilages which articulated with the palatoquadrates.
The palatoquadrates, which typically form the upper jaws in living cartilaginous fish, were reduced, immobile, and potentially fused partially with the cranium. This reduced state is unique among cartilaginous fish, and differs greatly from that seen in other eugeneodonts such as Helicoprion, in which the palatoquadrates were large and specialized, and potentially Fadenia and Sarcoprion, which may have had them entirely fused to the cranium (termed holostyly) or completely lost. The condition in O. hertwigi most closely resembled that of other caseodonts such as Caseodus and Eugeneodus, although the degree of reduction is much greater in Ornithoprion. The palatoquadrate articulated at the back of the neurocranium in a greatly limited, modified two jointed manner.
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