Dunkleosteus
| Dunkleosteus | ||||||||||||
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Skull of Dunkleosteus in the Queensland Museum |
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| Temporal occurrence | ||||||||||||
| Upper Devonian ( Famennium ) | ||||||||||||
| 380 to 360 million years | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Dunkleosteus | ||||||||||||
| Newberry , 1874 | ||||||||||||
Dunkleosteus ( Syn .: Dinichthys ) is one of the largest known representatives of the extinct Placodermi . It lived in the shallow seas of the youngest Upper Devonian ( Famennium ) about 380 to 360 million years ago .
The Placodermi
The Placodermi existed for a period of about 50 million years in the Middle Paleozoic . The placoderms are among the oldest jaw-bearing fish, the gnathostomata or jaw- mouthed fish . Dunkleosteus belongs to the species-richest group ( taxon ) of armored fish, the Arthrodira , which comprises two thirds of all known species. Within this taxon it was placed in the family Dinichthyidae by John Strong Newberry in 1885, now it belongs to the family of the Dunkleosteidae. With the genus Dunkleosteus , of which several species are known, the placoderms probably reached the climax of their development, in the Carboniferous following the Devonian no more placoderma fossils were found.
anatomy
Dunkleosteus could have reached a body length of up to six meters, for Dunkleosteus terelli information up to nine or ten meters have also been made. It was thus the top predator in its habitat ( biotope ) and the largest known animal of its time. The maximum weight is estimated to be over a ton. Most of the found parts of the animals consist only of the strong bony armor of the skull and neck area, a typical feature of arthrodesis. Since only these parts of the skeleton consist of a substance that can easily be fossilized, only this part of its anatomy has mostly been preserved. The shape of the unarmoured, movable part of its cartilaginous skeleton is not known, but it may have corresponded to the construction plan of the other arthrodirs. These are characterized by an asymmetrical or heterocerque tail fin , here the upper part is longer than the lower part, similar to that of many sharks .
The skin color of Dunkleosteus has not been recorded, but in 1997 the exceptionally well-preserved fossil of another tank fish was found in which skin pigment cells had been preserved. From this find you can still see that the animal had an iridescent, silver-colored belly and a red back. Hence it is believed that armored fish were also able to perceive colors.
Like all Placodermi, Dunkleosteus had no teeth. Their function was fulfilled by four constantly growing and self-sharpening bone plates in the upper and lower jaw. According to the latest functional morphological investigations of the skull of Dunkleosteus terelli , the bite force was 4400 Newtons at the tip of the snout and up to 5300 Newtons on the rear dental plates. So Dunkleosteus had a very strong bite force, but it remained far behind the bite force of the Megalodon ; the great white shark also has a stronger bite force than the dunkleosteus. The speed with which he could open and close his jaws was also extreme. It is possible that Dunkleosteus was one of the first fish to suck up its prey with a quick opening of its mouth. It was not possible to chew the prey with these jaw formations; this is also indicated by the fossils of half-digested whole fish, which were often found together with remains of Dunkleosteus .
After the extinction event at the end of the Devonian, there were no more descendants of the Dunkleosteus , while some of the much more agile large shark species took their place in the food pyramid.
Locations and fossil conservation
The fossil remains of this large tank fish have been found in the marine deposits of the USA, Morocco, Poland and Belgium. In the USA there are, among other things, localities in northeast Ohio near Cleveland on Lake Erie . There it is found in a black mudstone , the "Cleveland Shale" from the Upper Devonian ( Famennium ), known for its wealth of fossils , a member of the "Ohio Shale ". The frequency of the fossils is due to the deposit conditions, which favored the preservation of the organism remains. The black color of the rock indicates anoxic, i.e. oxygen-free, deposition conditions in the distant area ( pelagic ) of a shallow sea, where the remains of dead organisms sank to the bottom and there - without destructive bioturbation - were embedded in the muddy sediment . Finds of Dunkleosteus are also known from strata of the same age in other areas of the American Midwest .
designation
The generic name Dunkleosteus , composed of "dark" and osteos ( Greek : οστεος, bone ), was given in 1956 in honor of the paleontologist David Dunkle, the curator of the department of vertebrate palaeontology in the Cleveland Museum of Natural History , who studied the fossils of this Fish dealt. The type specimen of the genus is Dunkleosteus terelli , whose fossils were found in 1867 in the black mudstone on the banks of Sheffield Lake near Cleveland. At the end of the 19th century, there were a number of fossil hunters searching for the remains of the well-preserved Devonian fish in this area. One of them was Jay Terrell, who discovered the first Dunkleosteus . The fossil was described in 1873 by Dr. John Strong Newberry , who was from the Cleveland area and taught at Columbia University in New York. In his first description he counted the fish to the genus Dinichthys ("terrible fish") and gave it the species name terelli in honor of the finder Jay Terell. Finds from the Cleveland area have been exhibited at the British Museum , the American Museum of Natural History in New York, and other institutions since the Cleveland Museum of Natural History was not established until 1920. The genus Dunkleosteus was established by Lehman in 1956 to differentiate Dunkleosteus terelli from other species of the family Dinichthyidae, to which it belonged at the time.
species
Three to four species are counted in the genus Dunkleosteus :
- Dunkleosteus terrelli is the best preserved and studied species of the genus. Fossils have been found in the eastern United States and Belgium.
- Dunkleosteus marsaisi , whose fossils come from the Famennium of the Atlas Mountains in Morocco , had the same size and shape as Dunkleosteus terelli and is therefore often seen as a synonym for this. The snout is much narrower in Dunkleosteus marsaisi .
- Dunkleosteus amblyodoratus is known only from a few skull fragments found in the Upper Devonian layers of Kettle Point in Ontario , Canada . The plates in the neck area give the head the shape of a blunt spearhead. Its length is estimated at 6 meters.
- Dunkleosteus raveri was a small fish, probably only 1 meter long, of which an undamaged skull was found. He had relatively large eyes in relation to the size of his skull. Since it comes from a layer member of the "Ohio Shales", directly below the layers in which Dunkleosteus terelli was found, it could have belonged to the ancestors of this huge Dunkleosteus . It is named after Clarence Raver, who discovered the Appalachian deposits where the fossil was found.
Individual evidence
- ↑ Permanent collection of the Natural History Museum Vienna
- ↑ AM Murray: The Palaeozoic, Mesozoic and Cenozoic Early fishes of Africa . Fish and Fisheries, 1, 2, pp. 111-145, June 2000 doi : 10.1046 / j.1467-2979.2000.00015.x
- ↑ Dunkleosteus (Placodermi) Devonian Armored Fish from Morocco Pictures of the fossil at fossilmuseum.net
- ^ A b Robert K. Carr and William J. Hlavin: Two new species of Dunkleosteus Lehman, 1956, from the Ohio Shale Formation (USA, Famennian) and the Kettle Point Formation (Canada, Upper Devonian), and a cladistic analysis of the Eubrachythoraci (Placodermi, Arthrodira). Zoological Journal of the Linnean Society, 159, pp. 195-222, 2010 doi : 10.1111 / j.1096-3642.2009.00578.x
literature
- Philip SL Anderson, Mark W. Westneat: Feeding mechanics and bite force modeling of the skull of Dunkleosteus terrelli, an ancient apex predator. Biology Letters, Royal Society Publishing, 2006 doi : 10.1098 / rsbl.2006.0569 ( full text PDF ) (English).
Web links
- Dunkleosteus in the Cleveland Museum of Natural History.
- Skull of Dunkleosteus
- Live reconstruction by Dunkleosteus
