Dunkleosteus
Dunkleosteus | |
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Partially reconstructed D. terrelli skull and trunk armor (specimen CMNH 5768), Cleveland Museum of Natural History | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | †Placodermi |
Order: | †Arthrodira |
Suborder: | †Brachythoraci |
Family: | †Dunkleosteidae |
Genus: | †Dunkleosteus Lehman, 1956 |
Type species | |
†Dinichthys terrelli Newberry, 1873
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Species | |
List
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Dunkleosteus is an
Dunkleosteus consists of ten species, some of which are among the largest placoderms ("plate-skinned") to have ever lived: D. terrelli, D. belgicus, D. denisoni, D. marsaisi, D. magnificus, D. missouriensis, D. newberryi, D. amblyodoratus, D. raveri, and D. tuderensis. The largest and best known species is D. terrelli. Since body shape is not known, various methods of estimation put the living total length of the largest known specimen between 4.1 to 10 m (13 to 33 ft) long and weigh around 1–4 t (1.1–4.4 short tons).[2] However, lengths of 5 metres (16 ft) or more are poorly supported and the most extensive analyses support smaller size estimates.[2][3]
Dunkleosteus could quickly open and close its jaw, creating suction like modern-day suction feeders, and had a bite force that is considered the highest of any living or fossil fish, and among the highest of any animal. Fossils of Dunkleosteus have been found in North America, Poland, Belgium, and Morocco.
Discovery
Dunkleosteus fossils were first discovered in 1867 by Jay Terrell, a hotel owner and amateur
The largest collection of Dunkleosteus fossils in the world is housed at the
Taxonomy
Dunkleosteus was named by Jean-Pierre Lehman in 1956 to honour David Dunkle (1911–1984), former curator of vertebrate paleontology at the Cleveland Museum of Natural History. The genus name Dunkleosteus combines David Dunkle's surname with the Greek word ὀστέον (ostéon 'bone'), literally meaning "Dunkle's bone".[12]
Originally thought to be a member of the genus
The cladogram below from the study of Zhu & Zhu (2013) shows the placement of Dunkleosteus within Dunkleosteidae and Dinichthys within the separate clade Aspinothoracidi:[15]
Eubrachythoraci |
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Pachyosteomorphi | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Alternatively, the subsequent 2016 Zhu et al. study using a larger morphological dataset recovered Panxiosteidae well outside of Dunkleosteoidea, leaving the status of Dunkleosteidae as a clade grouping separate from Dunkleosteoidea in doubt, as shown in the cladogram below:[16]
Eubrachythoraci |
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Species
At least ten different species[13][17] of Dunkleosteus have been described so far. However, many of them are poorly characterized and may be synonyms of previously named species or not pertain to Dunkleosteus.[18] Dunkleosteus as currently defined is a wastebasket taxon for large dunkleosteoid arthrodires that are more evolutionarily derived than Eastmanosteus.[18]
The type species, D. terrelli, is the largest, best-known species of the genus. Size estimates for this species range from 4.1–10 m (13–33 ft) in length, though estimates greater than 4.5 m are poorly supported.[3][2] Skulls of this species can be up to 60–70 cm (24–28 in) in length.[2] D. terrelli's fossil remains are found in Upper Frasnian to Upper Famennian Late Devonian strata of the United States (Huron, Chagrin, and Cleveland Shales of Ohio, the Conneaut and Chadakoin Formations of Pennsylvania, the Chattanooga Shale of Tennessee, the Lost Burro Formation of California, and possibly the Ives breccia of Texas[17]) and Europe.
D. belgicus (?) is known from fragments described from the Famennian of Belgium. The median dorsal plate is characteristic of the genus, but, a plate that was described as a suborbital is an anterolateral.[17] Lelièvre (1982) considers this taxon a nomen dubium ("doubtful name") and suggests the material may actually pertain to Ardennosteus.[19]
D. denisoni is known from a small median dorsal plate, typical in appearance for Dunkleosteus, but much smaller than normal. It is comparable in skull structure to D. marsaisi.[17]
D. marsaisi refers to the Dunkleosteus fossils from the Lower Famennian Late Devonian strata of the Atlas Mountains in Morocco. It differs in size, the known skulls averaging a length of 35 centimetres (1.15 ft) and in form to D. terrelli. In D. marsaisi, the snout is narrower, and a postpineal fenestra may be present. Many researchers and authorities consider it a synonym of D. terrelli.[20] H. Schultze regards D. marsaisi as a member of Eastmanosteus.[17][21]
D. magnificus is a large placoderm from the Frasnian
D. missouriensis is known from fragments from Frasnian Missouri. Dunkle and Lane regard them as being very similar to D. terrelli.[17]
D. newberryi is known primarily from a 28 centimetres (11 in) long infragnathal with a prominent anterior cusp, found in the Frasnian portion of the
D. amblyodoratus is known from some fragmentary remains from Late Devonian strata of
D. raveri is a small species, possibly 1 meter long, known from an uncrushed skull roof found in a carbonate concretion from near the bottom of the Huron Shale, of the Famennian Ohio Shale strata. Besides its small size, it had comparatively large eyes. Because D. raveri was found in the strata directly below the strata where the remains of D. terrelli are found, D. raveri may have given rise to D. terrelli. The species name commemorates Clarence Raver of Wakeman, Ohio, who discovered the concretion containing the holotype.[13]
D. tuderensis is known from an infragnathal found in the lower-middle
In total, of the ten or so species listed above only four are agreed upon as valid species of Dunkleosteus by all researchers: D. terrelli (which may or may not include Dunkleosteus material from Morocco), D. raveri, D. tuderensis, and possibly D. amblyodoratus (which is known from limited material that appears distinct but is difficult to compare with other dunkleosteids). The taxonomy of early late Devonian (Frasnian) species is poorly established, whereas latest Devonian (Famennian) species are easily referable to this genus. This is not counting additional material assigned to Dunkleosteus sp. from the Famennian of California, Texas, Tennessee, and Poland.[18][23]
Description
Size and anatomy
Dunkleosteus was covered in dermal bone forming armor plates across its skull and front half of its trunk. This armor is often described as being over 2–3 inches (5.1–7.6 cm) thick,[24][13] but this is only across the thickened nuchal plate at the back of the skull.[13] Thickening of the nuchal plate is a common feature of eubrachythoracid arthrodires.[25][26] Across the rest of the body the armor is generally much thinner, only about 0.33–1 inch (0.84–2.54 cm) in thickness.[27] The plates of Dunkleosteus had both a hard cortical and a marrow-filled cancellous layer, unlike most teleost fishes and more similar to tetrapod bones.[2][28]
Mainly the armored frontal sections of specimens have been
Dunkleosteus is one of the largest known placoderms, with its maximum size being variably estimated as anywhere from 4.1–10 metres (13–33 ft) by different researchers.[31][32][11][33][2] However, most cited length estimates are speculative and lack quantitative or statistical backing, and lengths of 5 m (16 ft) or more are poorly supported.[11][2] Most studies that estimate the length of Dunkleosteus do not provide information as to how these estimates were calculated, the measurements used to scale them, or which specimens were examined. Most are implied to be based on either CMNH 5768 (the largest complete armor of Dunkleosteus) or CMNH 5936 (the largest known jaw fragment).
Most of the studies with well-defined methods produce lengths of 5 metres (16 ft) or less for Dunkleosteus terrelli,[2] with the exception of Ferrón et al. (2017), which produces larger estimates of 6.88–8.79 metres (22.6–28.8 ft) based on upper jaw perimeter of modern sharks.[11] However, arthrodires have proportionally larger mouths than modern sharks, making the lengths estimated by Ferrón et al. (2017) unreliable.[3] Upper jaw perimeter overestimates the size of complete arthrodires like Coccosteus and the estimates of Ferrón et al. (2017) result in Dunkleosteus having an extremely small head and hyper-elongate trunk relative to the known dimensions of the fossils.[3] If the reconstruction presented in Ferrón et al. (2017) is scaled to the known dimensions of CMNH 5768, it produces a length of 3.77 metres (12.4 ft).[3]
Carr (2010) estimated a 4.6 metres (15 ft) long adult individual of Dunkleosteus terrelli to have weighed 665 kilograms (1,466 lb), assuming a shark-like body plan and a similar length-weight relationship.[34] Engelman (2023), using an ellipsoid volumetric method, estimated weights of 950–1,200 kilograms (2,090–2,650 lb) for typical (3.41 metres (11.2 ft) long) adult Dunkleosteus, and weights of 1,494–1,764 kilograms (3,294–3,889 lb) for the largest (4.1 metres (13.5 ft) in this study) individual.[2] The higher weights by Engelman (2023) are mostly a result of the fact that arthrodires tend to have relatively deeper and wider bodies compared to sharks.[2]
An exceptionally preserved specimen of D. terrelli preserves a
Length estimations of D. terrelli
Study (author) | Year | Length | Method | Reference |
---|---|---|---|---|
Newberry | 1875 | 4.5–5.5 metres (15–18 ft) | Extrapolated from Coccosteus cuspidatus, measurements and specimen used unclear | [4] |
Newberry | 1889 | 4.5 metres (15 ft) | Unstated (implied extrapolation from Coccosteus) | [35] |
Dean | 1895 | 3 metres (9.8 ft) | Methods, measurements, and specimens unstated | [36] |
Hussakof | 1905 | 1.67 metres (5.5 ft) (AMNH FF 195) 3.79 metres (12.4 ft) (extrapolated to CMNH 5768 by Engelman 2023[2] assuming similar head-trunk proportions) |
Entering angle of body | [37] |
Anonymous | 1923 | 7.6 metres (25 ft) | Methods, measurements, and specimens used not stated | [38] |
Hyde | 1926 | 4.5–6 metres (15–20 ft) | Methods, measurements, and specimens used not stated | [39] |
Romer | 1966 | 9 metres (30 ft) | Methods, measurements, and specimens used not stated | [40] |
Colbert | 1969 | 9 metres (30 ft) | Methods, measurements, and specimens used not stated | [41] |
Denison | 1978 | 6 metres (20 ft) | Methods, measurements, and specimens used not stated | [17] |
Williams | 1992 | 5 metres (16 ft) | Methods, measurements, and specimens used not stated | [42] |
Janvier | 2003 | 6–7 metres (20–23 ft) | Methods, measurements, and specimens used not stated | [43] |
Young | 2003 | 6 metres (20 ft) | Methods, measurements, and specimens used not stated | [44] |
Anderson and Westneat | 2007 | 6 metres (20 ft) | Methods, measurements, and specimens used not stated | [31] |
Anderson and Westneat | 2009 | 10 metres (33 ft) | Methods, measurements, and specimens used not stated | [32] |
Carr | 2010 | 4.5–6 metres (15–20 ft) | Methods, measurements, and specimens used not stated | [34] |
Long | 2010 | 4.5–8 metres (15–26 ft) | Methods, measurements, and specimens used not stated | [45] |
Sallan and Galimberti | 2015 | 8 metres (26 ft) | Methods, measurements, and specimens used not stated | [46] |
Ferrón et al. | 2017 | 6.88 metres (22.6 ft) (average adult, CMNH 5768) 8.79 metres (28.8 ft) (largest individual, CMNH 5936) |
Upper jaw perimeter | [11] |
Long et al. | 2019 | 6–8 metres (20–26 ft) | Methods, measurements, and specimens used not stated | [47] |
Johanson et al. | 2019 | 3 metres (9.8 ft) (CMNH 50322) 7.1 metres (23 ft) (extrapolated to CMNH 5768 by Engelman 2023 assuming similar head-trunk proportions) |
Methods and measurements not stated | [48] |
Engelman | 2023 | 3.41 metres (11.2 ft) (average adult, CMNH 5768) 4.1 metres (13.5 ft) (largest individual, CMNH 5936) |
Orbit-opercular length (head length minus snout) | [2] |
Engelman | 2023 | 3.41 metres (11.2 ft) (average adult, CMNH 5768) | Skull length in Coccosteus | [2] |
Engelman | 2023 | 5.23 metres (17.2 ft) (average adult, CMNH 5768) | Infragnathal length in Coccosteus (source considers this estimate unreliable due to Dunkleosteus having a relatively larger mouth than Coccosteus) | [2] |
Engelman | 2023 | 3.47 metres (11.4 ft) (average adult, CMNH 5768) | Entering angle of body | [2] |
Engelman | 2023 | 3.88 metres (12.7 ft) (average adult, CMNH 5768) | Length of posteroventrolateral plate | [2] |
Engelman | 2023 | 3.40 metres (11.2 ft) (average adult, CMNH 5768) | Inferred location of pelvic girdle | [2] |
Paleobiology
Diet
Dunkleosteus terrelli possessed a
In addition, teeth of a chondrichthyan thought to belong to Orodus (Orodus spp.) were found in association with Dunkleosteus remains, suggesting that these were probably stomach contents regurgitated from the animal. Orodus is thought to be tachypelagic, or a fast-swimming pelagic fish. Thus, Dunkleosteus might have been fast enough to catch these fast organisms, and not a slow swimmer like originally thought.[11] Fossils of Dunkleosteus are frequently found with boluses of fish bones, semidigested and partially eaten remains of other fish.[49] As a result, the fossil record indicates it may have routinely regurgitated prey bones rather than digest them. Mature individuals probably inhabited deep sea locations, like other placoderms, living in shallow waters during adolescence.[50]
A specimen of Dunkleosteus (CMNH 5302), and Titanichthys (CMNH 9889), show damage said to be puncture damage from the bony fangs of other Dunkleosteus.[32]
Reproduction
Dunkleosteus, together with most other placoderms, may have also been among the first vertebrates to internalize egg fertilization, as seen in some modern sharks.[51] Some other placoderms have been found with evidence that they may have been viviparous, including what appears to have been an umbilical cord.[52]
Growth
See also
- List of placoderms
References
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Further reading
- Anderson, Philip S. L. (2008). "Shape Variation Between Arthrodire Morphotypes Indicates Possible Feeding Niches". Journal of Vertebrate Paleontology. 28 (4): 961–969. S2CID 86583150.