| Dunkleosteus | |
|---|---|
_(Cleveland_Shale_Member%2c_Ohio_Shale%2c_Upper_Devonian%3b_Rocky_River_Valley%2c_Cleveland%2c_Ohio%2c_USA)_21_(34001200911).jpg) | |
| Partially reconstructedD. 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 | |
| Species | |
List
| |
Dunkleosteus is anextinctgenus of largearthrodire ("jointed-neck") fish that existed during theLate Devonian period, about 382–358million years ago. It was apelagic fish inhabiting open waters, and one of the first vertebrateapex predators of anyecosystem.[1]
Dunkleosteus consists of ten species, some of which are among the largestplacoderms ("plate-skinned") to have ever lived:D. terrelli,D. belgicus,D. denisoni,D. marsaisi,D.magnificus,D. missouriensis,D. newberryi,D. amblyodoratus,D. raveri, andD. tuderensis. However, the validity of several of these species is unclear (see below). The largest and best known species isD. terrelli. Since body shape is not known, various methods of estimation put the living total length of the largest known specimen ofD. terrelli 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, with the most recent and extensive studies on the body shape and size ofD. terrelli producing estimated lengths of approximately 3.4 metres (11 ft) for typical adults and 4.1 metres (13 ft) for exceptionally large individuals of this species.[2][3][4]
Dunkleosteus could quickly open and close its jaw, creating suction like modern-daysuction 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 ofDunkleosteus have been found in the United States, Canada, Poland, Belgium, and Morocco.
Dunkleosteus fossils were first discovered in 1867 by Jay Terrell, a hotel owner and amateurpaleontologist who collected fossils in the cliffs alongLake Erie near his home ofSheffield Lake, Ohio (due west ofCleveland), United States. Terrell donated his fossils toJohn Strong Newberry and the Ohio Geological Survey, who in 1873 described all the material as belonging to a single newgenus andspecies:Dinichthys herzeri. However, with later fossil discoveries, by 1875 it became apparent multiple large fish species were present in theOhio Shale.Dinichthys herzeri came from the lowermost layer, theHuron Shale, whereas most of the fossils were coming from the youngerCleveland Shale and represented a distinct species.[5] Newberry named this more common species "Dinichthys"terrelli, after Terrell.[6] Most of Terrell's original collection does not survive, having been destroyed by a fire inElyria, Ohio, in 1873.[5][7]
The largest collection ofDunkleosteus fossils in the world is housed at theCleveland Museum of Natural History,[8] with smaller collections (in descending order of size) held at theAmerican Museum of Natural History,[9]Smithsonian National Museum of Natural History,[10]Yale Peabody Museum,[11] theNatural History Museum in London, and theCincinnati Museum Center. Specimens ofDunkleosteus are on display in many museums throughout the world (see table below), most of which are casts of the same specimen: CMNH 5768, the largest well-preserved individual ofD. terrelli.[2][12] The original CMNH 5768 is on display in the Cleveland Museum of Natural History.
Dunkleosteus was named byJean-Pierre Lehman in 1956 to honourDavid Dunkle (1911–1984), former curator ofvertebrate paleontology at the Cleveland Museum of Natural History. The genus nameDunkleosteus combines David Dunkle's surname with the Greek wordὀστέον (ostéon 'bone'), literally meaning "Dunkle's bone".[13]
Originally thought to be a member of the genusDinichthys,Dunkleosteus was later recognized as belonging to its own genus in 1956. It was thought to be closely related toDinichthys, and they were grouped together in thefamilyDinichthyidae. However, in thephylogenetic analysis of Carr and Hlavin (2010),Dunkleosteus andDinichthys were found to belong to separateclades of arthrodires:Dunkleosteus belonged to a group called theDunkleosteoidea whileDinichthys belonged to the distantly relatedAspinothoracidi. Carr & Hlavin resurrected the familyDunkleosteidae and placedDunkleosteus,Eastmanosteus, and a few other genera from Dinichthyidae within it.[14] Dinichthyidae, in turn, is left amonospecific family, though closely related to arthrodires likeGorgonichthys andHeintzichthys.[15]
_(Cleveland_Shale_Member%2c_Ohio_Shale%2c_Upper_Devonian%3b_Rocky_River_Valley%2c_Cleveland%2c_Ohio%2c_USA)_25_(34091142396).jpg)
Thecladogram below from the study of Zhu & Zhu (2013) shows the placement ofDunkleosteus withinDunkleosteidae andDinichthys within the separate cladeAspinothoracidi:[16]
| Eubrachythoraci |
| Pachyosteomorphi | |||||||||||||||||||||||||||||||||||||||||||||
Alternatively, the subsequent 2016 Zhuet al. study using a largermorphological dataset recoveredPanxiosteidae well outside ofDunkleosteoidea, leaving the status ofDunkleosteidae as a clade grouping separate from Dunkleosteoidea in doubt, as shown in the cladogram below:[17]
| Eubrachythoraci |
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
At least ten different species[14][18] ofDunkleosteus have been described so far. However, many of them are poorly characterized and may besynonyms of previously named species or not pertain toDunkleosteus.[19]Dunkleosteus as currently defined is awastebasket taxon for largedunkleosteoidarthrodires that are moreevolutionarily derived thanEastmanosteus.[19]
Thetype 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.[4][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, andCleveland Shales of Ohio, the Conneaut andChadakoin Formations ofPennsylvania, theChattanooga Shale of Tennessee, theLost Burro Formation of California, and possibly the Ivesbreccia of Texas[18]) andEurope.
D. belgicus (?) is known from fragments described from theFamennian ofBelgium. The median dorsal plate is characteristic of the genus, but, a plate that was described as a suborbital is an anterolateral.[18] Lelièvre (1982) considers thistaxon anomen dubium ("doubtful name") and suggests the material may actually pertain toArdennosteus.[20]
D. denisoni is known from a small median dorsal plate, typical in appearance forDunkleosteus, but much smaller than normal. It is comparable in skull structure toD. marsaisi.[18]
D. marsaisi refers to theDunkleosteus fossils from the Lower Famennian Late Devonian strata of theAtlas Mountains inMorocco. It differs in size, the known skulls averaging a length of 35 centimetres (1.15 ft) and in form toD. terrelli. InD. marsaisi, the snout is narrower, and a postpineal fenestra may be present. Many researchers and authorities consider it a synonym ofD. terrelli.[21] H. Schultze regardsD. marsaisi as a member ofEastmanosteus.[18][22]
D. magnificus is a large placoderm from the FrasnianRhinestreet Shale of New York. It was originally described asDinichthys magnificus by Hussakof and Bryant in 1919, then as "Dinichthys mirabilis" by Heintz in 1932. Dunkle and Lane (1971) moved it toDunkleosteus,[18] whereas Dennis-Bryan (1987) considered it to belong to the genusEastmanosteus.[23] This species has a skull length of 55 cm (22 in) and a total estimated length of approximately 3 m (9.8 ft).[19]
D. missouriensis is known from fragments from FrasnianMissouri. Dunkle and Lane regard them as being very similar toD. terrelli.[18] In his revision ofDunkleosteus taxonomy, Hlavin (1976) considers this species to be tentatively synonymous withD. terrelli (Dunkleosteus cf.D. terrelli).[24]
D. newberryi is known primarily from a 28 centimetres (11 in) long infragnathal with a prominent anterior cusp, found in the Frasnian portion of theGenesee Group of New York, and originally described asDinichthys newberryi.[18] Lebedev et al. (2023) notedD. newberryi has an unusually long marginal tooth row compared to other species ofDunkleosteus and lacks the accessory odontoids typical of this genus, suggesting it might not belong toDunkleosteus or even Dunkleosteoidea.[19]
D. amblyodoratus is known from some fragmentary remains from Late Devonian strata ofKettle Point Formation, Ontario. The species name means 'blunt spear' and refers to the way thenuchal and paranuchal plates in the back of the head form the shape of a blunted spearhead.[14]
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 FamennianOhio Shale strata. Besides its small size, it had comparatively large eyes. BecauseD. raveri was found in the strata directly below the strata where the remains ofD. terrelli are found,D. raveri may have given rise toD. terrelli. The species name commemorates Clarence Raver ofWakeman, Ohio, who discovered the concretion containing theholotype.[14]
D. tuderensis is known from an infragnathal found in the lower-middleFamennian-agedBilovo Formation of theTver Region in northwest Russia. The specific name refers to theMaliy Tuder River as the holotype was found on its bank.[19]
In total, of the ten or so species listed above only four are agreed upon as valid species ofDunkleosteus by all researchers:D. terrelli (which may or may not includeDunkleosteus material from Morocco),D. raveri,D. tuderensis, and possiblyD. amblyodoratus (which is known from limited material that appears distinct but is difficult to compare with other dunkleosteids). The taxonomy of early lateDevonian (Frasnian) species is poorly established, whereas latestDevonian (Famennian) species are easily referable to this genus. This is not counting additional material assigned toDunkleosteussp. from theFamennian of California, Texas, Tennessee, and Poland.[19][25]
Dunkleosteus was covered indermal bone forming armor plates across its skull and front half of itstrunk. This armor is often described as being over 2–3 inches (5.1–7.6 cm) thick,[26][14] but this is only across the thickened nuchal plate at the back of the skull.[14] Thickening of the nuchal plate is acommon feature ofeubrachythoracidarthrodires.[27][28] 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.[29] The plates ofDunkleosteus had both a hardcortical and a marrow-filledcancellous layer, unlike mostteleost fishes and more similar totetrapod bones.[2][30]
Mainly the armored frontal sections of specimens have beenfossilized, and consequently, the appearance of the other portions of the fish is mostly unknown.[31] In fact, only about 5% ofDunkleosteus specimens have more than a quarter of their skeleton preserved.[32] Because of this, many reconstructions of the hindquarters are often based on fossils of smallerarthrodires, such asCoccosteus, which have preserved hind sections,[2] leading to widely varying size estimates.[2]
Dunkleosteus terrelli 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.[33][34][12][35][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.[12][2] Most studies that estimate the length ofDunkleosteus terrelli do not provide information as to how these estimates were calculated, the measurements used to scale them, or which specimens were examined. Estimates in these studies are implied to be based on either CMNH 5768 (the largest complete armor ofD. terrelli) or CMNH 5936 (the largest known jaw fragment). Additionally, these reconstructions often requireDunkleosteus to lack many features consistent across the body plans of other arthrodires likeCoccosteus andAmazichthys.[3]
The most extensive analyses of body size and shape inDunkleosteus terrelli produce length estimates of ~3.4 metres (11 ft) for typical adults of this species, with very rare and exceptional individuals potentially reaching lengths of 4.1 metres (13 ft).[2][3] These estimates were calculated using several different size proxies (head length, orbit-opercular length [head length minus snout length], ventral shield length, entering angle, locations of the pectoral and pelvic girdles relative to total length), which produce largely similar results.[2][3] Statisticalmargins of error in these methods mean lengths as great as 3.7 metres (12 ft) in typical adults and 4.5 metres (15 ft) for exceptional individuals remain possible, but greater lengths result in proportions largely outside what is seen in otherarthrodires andjawed fishes more generally, especially in terms of the size of the head and trunk armor relative to the total length of the animal and the relative location of thepectoral andpelvic fins.[2][3] Indeed, the implied proportions under the upper ranges of the margins of error suggest even those lengths may be overly generous.[3] Lengths at the lower end of the margins of error are unlikely given the preserved lengths of the head and trunk armor.[2]
Most studies with well-defined methods produce lengths of 5 metres (16 ft) or less forDunkleosteus terrelli,[2] with the exception of Ferrónet 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.[12] However, arthrodires have proportionally larger mouths than modern sharks, making the lengths estimated by Ferrónet al. (2017) unreliable.[4] Upper jaw perimeter overestimates the size of complete arthrodires likeCoccosteus and the estimates of Ferrónet al. (2017) result inDunkleosteus having an extremely small head and hyper-elongate trunk relative to the known dimensions of the fossils.[4] The reconstruction presented in Ferrónet al. (2017) is also incorrectly scaled to the known dimensions of the fossil material; if scaled to the size of CMNH 5768, it produces a length of 3.77 metres (12.4 ft), agreeing with the shorter estimates in later studies.[4]
Carr (2010) estimated a 4.6 metres (15 ft) long adult individual ofDunkleosteus terrelli to have weighed 665 kilograms (1,466 lb), assuming a shark-like body plan and a similar length-weight relationship.[36] Engelman (2023), using anellipsoidvolumetric method, estimated weights of 950–1,200 kilograms (2,090–2,650 lb) for typical (3.41 metres (11.2 ft) long) adultDunkleosteus, 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 ofD. terrelli preserves apectoral fin outline withceratotrichia, implying that the fin morphology of placoderms was much more variable than previously thought, and was heavily influenced by locomotory requirements. This knowledge, coupled with the knowledge that fish morphology is more heavily influenced by feeding niche than phylogeny, allowed a 2017 study to infer thecaudal fin shape ofD. terrelli, reconstructing this fin with a strong ventral lobe, a highaspect ratio, narrowcaudal peduncle, in contrast to previous reconstructions based on theanguilliform caudal fin of coccosteomorph placoderms.[12]
The only vertebral remains known for Dunkleosteus are a small series of 16 vertebrae within the trunk armor of the specimen CMNH 50322.[37] Most of these vertebrae are highly fused, and have very prominent, laterally-projecting articular facets compared to other arthrodires.[3][37] Although many arthrodires show the incorporation of anterior vertebrae into asynarcual, in these species the fused region is small whereas the fused region ofDunkleosteus extends almost to the end of the trunk armor, which would make its spine very stiff.[37][3] This, along with a ridge on the inside of the trunk armor suggesting an unusually well-developed attachment for the horizontal septum, suggestsDunkleosteus may have had an anteriorly stiffened spine and specialized connective tissues to transmit force generated by the anterior trunkmuscles to the tail fin, similar tothunniform vertebrates likelamnids andtunas.[3]
The pelvic girdle ofDunkleosteus is relatively small relative to the overall size of the armor.[3] Several specimens preserve associated pelvic girdles, but their original position was not recorded during preservation.[3] However, because these specimens were excavated from cliff faces, they were probably found in close to the armor, suggesting these fins were associated with the end of the ventral shield as in other arthrodires.[3] One specimen may preserve pelvic fin basals near the end of the trunk armor.[3]
| Study (author) | Year | Length | Method | Reference |
|---|---|---|---|---|
| Newberry | 1875 | 4.5–5.5 metres (15–18 ft) | Extrapolated fromCoccosteus cuspidatus, measurements and specimen used unclear | [5] |
| Newberry | 1889 | 4.5 metres (15 ft) | Unstated (implied extrapolation fromCoccosteus) | [38] |
| Dean | 1895 | 3 metres (9.8 ft) | Methods, measurements, and specimens unstated | [39] |
| 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 | [40] |
| Anonymous | 1923 | 7.6 metres (25 ft) | Methods, measurements, and specimens used not stated | [41] |
| Hyde | 1926 | 4.5–6 metres (15–20 ft) | Methods, measurements, and specimens used not stated | [42] |
| Romer | 1966 | 9 metres (30 ft) | Methods, measurements, and specimens used not stated | [43] |
| Colbert | 1969 | 9 metres (30 ft) | Methods, measurements, and specimens used not stated | [44] |
| Denison | 1978 | 6 metres (20 ft) | Methods, measurements, and specimens used not stated | [18] |
| Williams | 1992 | 5 metres (16 ft) | Methods, measurements, and specimens used not stated | [45] |
| Janvier | 2003 | 6–7 metres (20–23 ft) | Methods, measurements, and specimens used not stated | [46] |
| Young | 2003 | 6 metres (20 ft) | Methods, measurements, and specimens used not stated | [47] |
| Anderson and Westneat | 2007 | 6 metres (20 ft) | Methods, measurements, and specimens used not stated | [33] |
| Anderson and Westneat | 2009 | 10 metres (33 ft) | Methods, measurements, and specimens used not stated | [34] |
| Carr | 2010 | 4.5–6 metres (15–20 ft) | Methods, measurements, and specimens used not stated | [36] |
| Long | 2010 | 4.5–8 metres (15–26 ft) | Methods, measurements, and specimens used not stated | [48] |
| Sallan and Galimberti | 2015 | 8 metres (26 ft) | Methods, measurements, and specimens used not stated | [49] |
| Ferrónet 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 | [12] |
| Longet al. | 2019 | 6–8 metres (20–26 ft) | Methods, measurements, and specimens used not stated | [50] |
| Johansonet 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 | [37] |
| 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 inCoccosteus | [2] |
| Engelman | 2023 | 5.23 metres (17.2 ft) (average adult, CMNH 5768) | Infragnathal length inCoccosteus (source considers this estimate unreliable due toDunkleosteus having a relatively larger mouth thanCoccosteus) | [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] |
Dunkleosteus terrelli possessed afour-bar linkage mechanism forjaw opening that incorporated connections between the skull, the thoracic shield, the lower jaw and the jaw muscles joined by movable joints.[34][33] This mechanism allowedD. terrelli to both achieve a high speed of jaw opening, opening their jaws in 20 milliseconds and completing the whole process in 50–60 milliseconds (comparable to modern fishes that usesuction feeding to assist in prey capture[33]) and producing high bite forces when closing the jaw, estimated at 4,414 N (450 kgf; 992 lbf) at the tip and 5,363 N (547 kgf; 1,206 lbf) at the blade edge,[33] or even up to 6,170 N (629 kgf; 1,387 lbf) and 7,495 N (764 kgf; 1,685 lbf) respectively.[34] The bite force is considered the highest of any living or fossil fish, and among the highest of any animal.[33] The pressures generated in those regions were high enough to puncture or cut throughcuticle ordermal armor,[33] suggesting thatD. terrelli was adapted to prey on free-swimming, armored prey such asammonites and other placoderms.[34]
In addition, teeth of achondrichthyan thought to belong toOrodus (Orodus spp.) were found in association withDunkleosteus remains, suggesting that these were probably stomach contents regurgitated from the animal.Orodus is thought to be tachypelagic, or a fast-swimmingpelagic fish. Thus,Dunkleosteus might have been fast enough to catch these fast organisms, and not a slow swimmer like originally thought.[12] Fossils ofDunkleosteus are frequently found withboluses of fish bones, semidigested and partially eaten remains of other fish.[51] As a result, thefossil 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.[52]
A specimen ofDunkleosteus (CMNH 5302), andTitanichthys (CMNH 9889), show damage said to be puncture damage from the bony fangs of otherDunkleosteus.[34]
Dunkleosteus, together with most other placoderms, may have also been among the firstvertebrates tointernalize egg fertilization, as seen in some modern sharks.[53] Some other placoderms have been found with evidence that they may have beenviviparous, including what appears to have been anumbilical cord.[54]
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Morphological studies on the lower jaws of juveniles ofD. terrelli reveal they were proportionally as robust as those of adults, indicating they already could produce high bite forces and likely were able to shear into resistant prey tissue similar to adults, albeit on a smaller scale. This pattern is in direct contrast to the condition common intetrapods in which the jaws of juveniles are moregracile than in adults.[55]
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