Dunkleosteus

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Dunkleosteus telleri

Conservation status

Extinct (fossil)

Scientific classification

Kingdom:	Animalia
Phylum:	Chordata
Subphylum:	Vertebrata
Class:	Placodermi
Order:	Arthrodira
Family:	Dinichthyidae
Genus:	Dunkleosteus
Species:	Dunkleosteus telleri

Dunkleosteus
Translation	Dunkle's bones
Type	fish, placoderm
Length	20-33 ft (6-10 m)
Weight	4 tons
Age	370-360 million years ago
Diet	carnivore
Environment	ocean
Distribution	Morocco, Belgium, Poland and USA

Dunkleosteus was a large Placoderm (armoured prehistoric fish) that lived in the late Devonian period, about 360 – 415 million years ago. The largest of the genus grew to around 8 to 10 m (27 to 33 feet) long, and were probably the top predators of their time.

1 Description
2 Notes
3 References
4 External links

[edit] Description

Dunkleosteus, named to honour Dr. David Dunkle, former curator of Vertebrate Paleontology at the Cleveland Museum of Natural History, was probably the largest member of the Placodermi, a Class of armour-plated fishes. The Placodermi first started appearing in the Silurian, and all of them were extinct by the late Devonian. There are no modern descendants.

Due to its heavily armoured nature, Dunkleosteus was likely a relatively slow (albeit massively powerful) swimmer, and may have encountered stiff competition from the smaller yet swifter sharks who had then only recently evolved. It is presumed to have dwelled in diverse zones of inshore waters, although it is unknown whether or not it was also somewhat pelagic, that is, swimming freely in open ocean. Fossilization tends to have preserved only the especially armoured frontal sections of specimens, and thus it is uncertain what exactly the hind sections of this ancient fish were like.

Dunkleosteus skull, Queensland Museum

A skull of Dunkleosteus is on display in the Queensland Museum in Brisbane, Queensland (pictured).

By Devonian standards, Dunkleosteus was highly evolved. It was one of the earliest jawed fishes. Instead of actual teeth, Dunkleosteus possessed two long, bony blades that could slice through flesh and snap and crush bones and almost anything else. After studying a biomechanical model of the fish's jaws, scientists at the Field Museum of Natural History and the University of Chicago concluded that Dunkleosteus had the most powerful bite of any fish, well ahead of sharks, including the Great White. Dunkleosteus could concentrate a pressure of up to 8,000 pounds-force per square inch (55 megapascals) at the tip of its mouth, effectively placing Dunkleosteus in the league of Tyrannosaurus rex and modern crocodiles as having the most powerful known bite. ^[1] Dunkleosteus could also open its mouth in one-fiftieth of a second, which would have caused a powerful suction that pulled the prey into its mouth, a food-capture technique reinvented by many of the most advanced teleost fishes today.

It was a vicious hunter, and probably ate whatever it could find, including sharks and probably other Dunkleosteus. It was a glutton, as well. Frequently, fossils of Dunkleosteus are found with semi-digested and partially eaten remains of other fish. As a result, the fossil record indicates that it may have routinely regurgitated prey bones rather than dissolving them. Dunkleosteus, like most other Placoderms, may have also been among the first vertebrates to internalize egg fertilization, akin to the modern process of vivipary, and thus sexually reproduce in the manner that most mammals and sharks do today.^[2]

Although Placoderms only existed for 60 million years, their mark on the fossil record is quite visible. They were a pioneer in the later scenes of the Paleozoic, and were vital to the success of the vertebrates. The Placoderms died out in the late Devonian for reasons that are still not well understood. See Late Devonian extinction.

They were found in Morocco, Belgium, Poland, and North America.

[edit] Notes

^ Philip S.L. Anderson and Mark W. Westneat (2006) "Feeding mechanics and bite force modelling of the skull of Dunkleosteus terrelli, an ancient apex predator", Biology letters, pp 76-79, A 2006 study of the biomechanics of D.terreli, interpreted fossil jaws to build a computer model of the fish's bones and muscles and determined that it could tear apart its food with a force of 500 kgf per inch (193 kN/m).
^ The first recorded sexual dimorphism appeared in the middle-Devonian ptycotodontid placoderm Rhamphodopsis, which had external clasping organs on males that are strong indicators of intromittent sexual intercourse and internal fertilization. Claspers are modified structures at the base of the pelvic fins which transmit sperm directly inside the female. Females had wide pelvic basal plates. See Placoderm.