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Temporal range: Carboniferous
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Subclass: Holocephali
Order: †Eugeneodontida
Family: †Caseodontidae
Genus: †Ornithoprion
Zangerl, 1966
Type species
Ornithoprion hertwigi
Zangerl, 1966

Ornithoprion ("bird saw") is a monotypic genus of extinct eugeneodont holocephalan in the family Caseodontidae. The type and only species, O. hertwigi, lived during the Moscovian stage of the Carboniferous, between 315.2 to 307 million years ago,[1] and is known from black shale deposits in what is now the Midwestern United States. The discovery and description of Ornithoprion, performed primarily via radiography, helped clarify the cranial anatomy of the eugeneodonts, a group which were previously known primarily from isolated tooth whorls. The genus derives its name from the elongate, bill-like rostrum and large eyes, which vaguely resemble the features of a bird,[2] while the species name honors Oscar Hertwig.

Discovery and specimens edit

 
Stratigraphy of the Illinois Basin, where O. hertwigi's fossils have been found

The genus and species were named and described in 1966, by geologist Rainer Zangerl, in a paper published by the Field Museum of Natural History (then the Chicago Museum of Natural History).[3] This description was based on material collected primarily from the Mecca Quarry of Indiana, in black shale which is part of the Linton Formation. A single specimen was also collected from the Logan Quarry in an exposure of the Staunton Formation, and another from a coal mine near Wilmington, Illinois. All specimens are preserved in organic black shales, with the Illinois specimen being described as pyritic.[2] The Mecca and Logan Quarry material has been dated to the Moscovian stage of the Carboniferous (Desmoinesian stage in American regional stratigraphy),[4][3] which is part of the Pennsylvanian subperiod. The precise age and locality of the Illinois specimen is unknown due to it being held in a private collection. Nine specimens were initially described, with CNHM PF-2710 from the Mecca quarry being designated as the holotype.[2] Multiple additional specimens have subsequently been assigned to Ornithoprion, including occurrences from the Excello Shale of Indiana.[5][6]

Like many other chondrichthyans from the Mecca and Logan quarries,[7] the studies of the holotype and paratypes of Ornithoprion were primarily performed by radiographic imaging. The specimens were not extracted from the surrounding matrix, but were instead stereoscopically scanned via X-rays, with the calcified elements of their skeletons appearing clearly against the rock. The captured stereoscopic images were subsequently overlaid and printed onto either paper or film, or traced onto clear plastic to produce diagrammatic figures. The Staunton Formation specimen, CNHM PF-2656, was also cut into multiple cross-sections, with these being ground down to reveal the internal anatomy of the placoid scales and teeth.[2]

Description edit

O. hertwigi is known from multiple articulated but incomplete specimens, with none preserving skeletal material beyond the pectoral girdle. Most of this material is preserved in lateral view and all, including the holotype, is heavily compressed.[2][3] The preserved portion of the skeleton was composed primarily of cartilage reinforced by prismatic tesserae, structures which are present in the skeletons of modern Elasmobranchs but which are not apparent in living chimaeras.[8] These tesserae are also known from other members of Eugeneodontida and are not unique to Ornithoprion.[9] While the postcranial anatomy is incompletely known, it was likely similar to other caseodontids such as Fadenia and Romerodus, with a streamline body, a homocercal caudal fin, and reduced or absent pelvic fins. The dorsal and pectoral fins of Ornithoprion are also unknown, but there is no indication they possessed fin spines like many other Carboniferous Chondrichthyans.[10] At least five branchial arches are present,[11] although it is unknown if these supported individual gill slits or an operculum.[2]

Skull and teeth edit

The most diagnostic trait of Ornithoprion is the exaggerated rostrum extending from the mandible, which is nearly the length of the rest of the skull. The rostrum, as well as a correlating section of the upper jaw, were armored and reinforced by calcified rods, which appear to have been dermal structures formed separately from the underlying cartilage.[12] The mandibular rostrum is connected to the Meckel's cartilage (lower jaw) by an unfused joint, with a single whorl of teeth positioned along the midline near the base of the rostrum where it meets the jaw. A keel of cartilage extends off of the rostrum from below, correlating with the position of the whorl. The tip of the rostrum is extremely elongated, and according to Zangerl's description was likely to have been cylindrical in cross section and spear-like in life.[2] There is no evidence that sensory structures were present within the rostrum.[13] The Meckel's cartilage itself consists of a pair of thin, flattened cartilage rods which support the rostrum and which attach to the palatoquadrate at two points.[2]

 
Restored skull of the distantly related Helicoprion, displaying well-developed palatoquadrate and lack of a mandibular rostrum

The chondrocranium is long and pointed, with large orbits which lack preserved scleral rings. An indentation set far forward on the snout is reported by Zangerl to have likely held the nasal capsule,[2] although it is also unpreserved. The palatoquadrate, which typically forms the upper jaw of living cartilaginous fish, is reduced and immobile, and articulates with the chondrocranium in an autodiastylic, unfused manner.[10] The reduced state differs greatly from that of the eugeneodonts Helicoprion and Edestus, in which the palatoquadrates are large and specialized,[9][14][15] and potentially from Sarcoprion, which may have them fused to the cranium.[2] The palatoquadrate seen in Ornithoprion is most similar to that seen in other caseodonts such as Caseodus, which typically share its thin, band-like shape and limited articulation.[10] The remains of what Zangerl speculated to be part of the hyoid arch are also present along the back of the skull.[2]

The lower teeth of O. hertwigi consist of both multiple large tooth crowns extending from a single root, known as a tooth whorl,[15] and of pavement teeth. The pavement teeth, which are plate-like, flattened, and rectangular, were present on both the upper and lower jaw and possessed deep pits and grooves in their surface. The structure of these teeth was compared with the tooth pavement of Erikodus, a related genus, in Zangerl's 1966 description.[2] The symphyseal whorl, a characteristic trait of the eugeneodonts, possess up to seven broad, rounded tooth crowns, with the largest figured whorls spanning approximately 1 cm (.39 in) in length.[10] The tooth crowns on the lower whorl vary in size, with the smallest teeth being situated at the front of the whorl and the largest at the back. It is thought that V-shaped teeth were present in another symphyseal row attached directly to the chondrocranium. These teeth, the largest figured being approximately 4 mm (.16 in) in length, were significantly different than those of the lower jaw, and the two likely contacted each other during feeding. Zangerl noted, however, that due to the nature of the material's preservation, the precise arrangement of O. hertwigi's dentition is unknown.[2]

Postcranial skeleton edit

The known postcrania of Ornithoprion encompasses the anterior-most portion of the skeleton. The unfused scapulocoracoids are described by Zangerl to be of "selachian pattern" to denote vague similarity to those of modern sharks,[2] although the dorsal scapular portion is forward-facing, and the coracoidal portion is relatively large, which along with their unfused nature is in contrast to sharks. Either five or six pairs of ceratobranchials are present,[11] with what Zangerl tentatively identifies as sternal cartilage running beneath them.[2] This unpaired intercoracoidal cartilage has also be identified in living broadnose sevengill sharks,[16] as well as the extinct Iniopterygians, Jurassic Chimaeriform Ischyodus,[17] and potentially Fadenia.[11] The function of this structure in Ornithoprion is unknown, although it is likely homologous to similar, paired cartilage structures observed in other extinct chondrichthyans.[10]

Like many Paleozoic chondrichthyans, the vertebral centra of Ornithoprion were likely uncalcified and are unpreserved, although a series of diamond-shaped cartilage structures are present along the expected path of the vertebral column. These cartilage structures are proposed by Zangerl to represent heavily modified neural arches, the anatomy of which is unique to O. hertwigi. It is possible these structures are an adaptation to the morphology or function of the animal's skull.[2]

Dermal denticles edit

Unlike living chimaeras, in which scales are only present in isolated regions,[8] the known body of Ornithoprion was completely covered in tiny denticles similar to those of sharks. These denticles possessed a pulp cavity, dentin, and enameloid, and grew from a flattened base, much like those of modern cartilaginous fish. However, Zangerl claims that the denticlular bases of Ornithoprion were composed of bone, rather than dentin, and observed that many denticles form fused, compound, polydontode scales, which are not known among living chondrichthyans. These compound denticles share a single base with multiple crowns and pulp cavities emerging from it, and in O. hertwigi may consist of more than seven crowns sharing a single base.[2] Similar polydontode scales are known to occur in the related Sarcoprion and potentially Helicoprion,[18] as well as in a number of other extinct chondrichthyans, although these lack any indication of bone.[8]

If Zangerl's interpretation of the dermal structures of O. hertwigi as bone is correct, it would represent the only example of bone among extinct euchondrocephalans, which otherwise have scales and armor composed of dentin.[8]

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 polydontous denticles. He likens this phenomenon to that proposed by Oscar Hertwig as an explanation for the origin of the vertebrate dermal armor, and although Zangerl acknowledges that this adaptation is almost definitely convergent in Ornithoprion, he honors Hertwig's hypothesis in the name of the type species: Ornithoprion hertwigi.[2]

Classification edit

Though often referred to as sharks in both formal and informal texts, the eugeneodonts are only very distant relatives of living sharks. In the initial description, Ornithoprion was placed as a member of Edestidae under the order (sometimes class) Bradyodonti.[2][8][18] In his revised classification scheme from 1981, however, Zangerl placed O. hertwigi as a member of the Caseodontidae, as part of a larger superfamily Caseodontoidea and order Eugeneodontida, in light of the numerous new taxa that had been observed since Ornithoprion's original description.[10] This classification is still tentatively followed today,[11] with Eugeneodontida itself typically being regarded as a stem group of the subclass Holocephali or Euchondrocephali and as part of a monophyletic Chondrichthyes.[15][19] Euchondrocephali is today only represented by the chimaeras, and the higher level interrelationships between extinct members of the subclass remain enigmatic.[20]

The skull and vertebral morphology of Ornithoprion is wildly different from that of other known eugeneodonts,[11] and key elements of the postcranial skeleton are missing.[2] Its assignment among the Caseodontidae is based on similarities in dentition and similar reduction of the palatoquadrate to that seen in genera such as Caseodus.[21] Zangerl (1981) places Ornithoprion as a sister taxon to a clade containing Erikodus and Fadenia.[10]

Paleobiology and paleoecology edit

 
Orodus greggi, another component of the Logan Quarry fauna, on display at the Field Museum of Natural History

The Mecca, Logan, and Excello shales all represent marine depositional environments, and all preserve a diverse assemblage of species.[6][7]

Numerous specimens of Ornithoprion show direct evidence of feeding traces left by predators or scavengers, resulting in portions of the skeleton often being broken, maimed or missing.

Like many of its close relatives, Ornithoprion is believed to have been a durophage which fed on benthic invertebrates.

The function of O. hertwigi's armored rostrum remains unclear. Zangerl (1966) proposes its use to disturb or probe sediment while hunting for prey living on or within the seabed, as well as potentially flinging dislodged prey into the water column, but notes this proposal is entirely speculative.[2] The anatomy of the mandibular rostrum is inconsistent with its use as a sensory structure,[13] while the dentition makes it appear unlikely the species fed near the surface like the living halfbeaks. 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, but use of the rostrum as a weapon is considered by him to be unlikely. The mandibular rostrum of Ornithoprion is said to most closely resemble those of the extinct actinopterygians Saurodon and Saurocephalus, in which the function is also not confidently known.[2]

See also edit

Alienacanthus

References edit

  1. ^ "Ornithoprion hertwigi". Mindat.org. Retrieved 23 April 2024.
  2. ^ a b c d e f g h i j k l m n o p q r s t u v Zangerl, Rainer (17 March 1966). "A new shark of the family Edestidae, Ornithoprion hertwigi, from the Pennsylvanian Mecca and Logan quarry shales of Indiana". Fieldiana Geology. 16. Chicago Field Museum of Natural History: 1–42. Retrieved 14 March 2020.
  3. ^ a b c "PBDB Taxon". The Paleobiology Database.
  4. ^ "International Commission on Stratigraphy Subcommission on Carboniferous Stratigraphy". carboniferous.stratigraphy.org. Retrieved 2024-04-23.
  5. ^ "Ornithoprion Zangerl, 1966". www.gbif.org. Retrieved 2024-04-25.
  6. ^ a b Williams, Michael E. (1979). "The 'Cladodont' level sharks of the Pennsylvanian black shales of central North America". Palaeontographica – via ProQuest.
  7. ^ a b Zangerl, Rainer; Richardson, Eugene S. (1963). The paleoecological history of two Pennsylvanian black shales. Fieldiana. Chicago: Chicago Natural History Museum.
  8. ^ a b c d e "The phylogeny of the chimaeroids". Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences. 249 (757): 101–219. 1965-06-10. doi:10.1098/rstb.1965.0010. ISSN 2054-0280.
  9. ^ a b Tapanila, Leif; Pruitt, Jesse; Pradel, Alan; Wilga, Cheryl D.; Ramsay, Jason B.; Schlader, Robert; Didier, Dominique A. (2013-04-23). "Jaws for a spiral-tooth whorl: CT images reveal novel adaptation and phylogeny in fossil Helicoprion". Biology Letters. 9 (2): 20130057. doi:10.1098/rsbl.2013.0057. ISSN 1744-9561.
  10. ^ a b c d e f g Zangerl, Rainer (1981). Chondrichthyes 1: Paleozoic Elasmobranchii (Handbook of Paleoichthyology). Friedrich Pfell (published January 1, 1981). pp. 74–94. ISBN 978-3899370454.
  11. ^ a b c d e Mutter, Raoul J.; Neuman, Andrew G. (2008-01-01) [2008-01-01]. "New eugeneodontid sharks from the Lower Triassic Sulphur Mountain Formation of Western Canada". Geological Society, London, Special Publications. 295 (1): 9–41. doi:10.1144/SP295.3. ISSN 0305-8719.{{cite journal}}: CS1 maint: date and year (link)
  12. ^ HALL, BRIAN K. (1975). "Evolutionary Consequences of Skeletal Differentiation". American Zoologist. 15 (2): 329–350. doi:10.1093/icb/15.2.329. ISSN 0003-1569.
  13. ^ a b Poplin, Cécile M. (1978). "An Actinopterygian with a Long Rostrum from the Pennsylvanian of Logan Quarry, Indiana". Journal of Paleontology. 52 (3): 524–531. ISSN 0022-3360.
  14. ^ Ramsay, Jason B.; Wilga, Cheryl D.; Tapanila, Leif; Pruitt, Jesse; Pradel, Alan; Schlader, Robert; Didier, Dominique A. (2014-01-18). "Eating with a saw for a jaw: Functional morphology of the jaws and tooth‐whorl in H elicoprion davisii". Journal of Morphology. 276 (1): 47–64. doi:10.1002/jmor.20319. ISSN 0362-2525. Retrieved 17 April 2024.
  15. ^ a b c Tapanila, Leif; Pruitt, Jesse; Wilga, Cheryl D.; Pradel, Alan (2018-12-26). "Saws, Scissors, and Sharks: Late Paleozoic Experimentation with Symphyseal Dentition". The Anatomical Record. 303 (2): 363–376. doi:10.1002/ar.24046. ISSN 1932-8486.
  16. ^ PARKER, T. JEFFERY (1891-04-02). "On the Presence of a Sternum in Notidanus indicus". Nature. 43 (1118): 516–516. doi:10.1038/043516b0. ISSN 0028-0836.
  17. ^ Pradel, Alan; Tafforeau, Paul; Janvier, Philippe (2010-03-04). "Study of the pectoral girdle and fins of the Late Carboniferous sibyrhynchid iniopterygians (Vertebrata, Chondrichthyes, Iniopterygia) from Kansas and Oklahoma (USA) by means of microtomography, with comments on iniopterygian relationships". Comptes Rendus Palevol. 9 (6–7): 377–387. doi:10.1016/j.crpv.2010.07.015. ISSN 1631-0683.
  18. ^ a b Lebedev, O. A. (2009-05-18). "A new specimen of Helicoprion Karpinsky, 1899 from Kazakhstanian Cisurals and a new reconstruction of its tooth whorl position and function". Acta Zoologica. 90 (s1): 171–182. doi:10.1111/j.1463-6395.2008.00353.x. ISSN 0001-7272.{{cite journal}}: CS1 maint: date and year (link)
  19. ^ Duffin, Christopher J. (2015-10-14). "Cochliodonts and chimaeroids: Arthur Smith Woodward and the holocephalians". Geological Society, London, Special Publications. 430 (1): 137–154. doi:10.1144/sp430.9. ISSN 0305-8719.
  20. ^ Lund, Richard; Grogan, Eileen D. (March 1997). "Relationships of the Chimaeriformes and the basal radiation of the Chondrichthyes". Reviews in Fish Biology and Fisheries. 7 (1): 65–123. doi:10.1023/A:1018471324332.
  21. ^ Schultze, Hans-Peter; West, Ronald R. (1996). "An eugeneodontid elasmobranch from the Late Paleozoic of Kansas". Journal of Paleontology. 70 (1): 162–165. doi:10.1017/S0022336000023192. ISSN 0022-3360.
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