Dunkleosteus

Dunkleosteus Temporal range: Late Devonian, 380–360 Ma PreЄ Є O S D C P T J K Pg N
Reconstructed skull, Queensland Museum
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	†Placodermi
Order:	†Arthrodira
Family:	†Dunkleosteidae
Genus:	†Dunkleosteus Lehman, 1956
Type species
Dinichthys terrelli Newberry, 1873
Species
D. terrelli (Newberry, 1873 [originally Dinichthys]) ?D. marsaisi Lehmann, 1956 D. amblyodoratus Carr & Hlavin, 2010 D. raveri Carr & Hlavin, 2010
Synonyms
Ponerichthys Miller, 1892

Dunkleosteus (From "(David) Dunkle" + osteus (οστεος, Greek: bone); meaning "Dunkle's Bone") is a genus of prehistoric fish, one of the largest arthrodire placoderms ever to have lived, existing during the Late Devonian period, about 380-360 million years ago.

This hunter, measuring up to 10 metres (33 ft)^[1][2] and weighing 3.6 tonnes (4.0 short tons),^[3] was a hypercarnivorous apex predator. Few other placoderms, save, perhaps, its contemporary, Titanichthys, rivaled Dunkleosteus in size.

Dunkleosteus is a member of the pachyosteomorph arthrodires, and is more specifically usually placed in the family Dinichthyidae, a family composed mostly of large, carnivorous arthrodires like Gorgonichthys. Anderson (2009) suggests that because of its primitive jaw structure Dunkleosteus should be placed outside the family Dinichthyidae, perhaps close to the base of the clade Pachyosteomorpha, near Eastmanosteus,^{[citation needed]} but this idea has yet to be tested.

New studies have revealed several features in both its food and biomechanics as its ecology and physiology. Placodermi first appeared in the Silurian, and the group became extinct during the transition from the Devonian to the Carboniferous, leaving no descendants. The class lasted barely 50 million years, in comparison to the 400 million year long history of sharks.^[4]

In recent decades, Dunkleosteus has achieved recognition in popular culture, with a large number of specimens on display, and notable appearances in entertainment media. Numerous fossils of some species have been found in North America, Poland, Belgium and Morocco.

Description

Life restoration of Dunkleosteus

Due to its heavily armoured nature, Dunkleosteus was likely a relatively slow, but powerful, swimmer. It is thought to have dwelled in diverse zones of inshore waters. 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. As such, the reconstructions of the hindquarters are often based on smaller arthrodires, such as Coccosteus, that had hind sections preserved.

The most famous specimens of Dunkleosteus are displayed at the Cleveland Museum of Natural History. Others are displayed at the American Museum of Natural History and in the Queensland Museum in Brisbane, Queensland.

Front view of a Dunkleosteus skull, Musée national d'Histoire naturelle, Paris

Instead of teeth, Dunkleosteus possessed two pairs of sharp bony plates which formed a beak-like structure. 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 second most powerful bite of any fish (the giant Megalodon being the strongest). Dunkleosteus could concentrate a pressure of up to 8,000 pounds per square inch (55 MPa) at the tip of its mouth, placing Dunkleosteus in the same league as Tyrannosaurus rex and modern crocodiles as having the most powerful known bite.^[5]

Dunkleosteus could open its mouth in one-fiftieth of a second, which would have caused a powerful suction that pulled the prey into its mouth,^[5] a food-capture technique used by many fish today.

A skull diagram of Dunkleosteus

The discovery of Dunkleosteus armor with unhealed bite marks strongly suggest that they cannibalized each other when the opportunity arose. Frequently, fossils of Dunkleosteus are found with boluses of fish bones, semi-digested and partially eaten remains of other fish.^[4] As a result, the fossil record indicates that it may have routinely regurgitated prey bones rather than digest them.

Dunkleosteus, like most other placoderms, may have also been among the first vertebrates to internalize egg fertilization, as seen in some modern sharks.

Reconstruction of Dunkleosteus

Morphological studies done on the "jaw bones" (inferognathals) of juvenile and adult Dunkleosteus suggest that Dunkleosteus went through a change in jaw morphology and diet as it aged. Juveniles had stiffer jaws more similar to Coccosteus, and appear to have fed on various soft-bodied aquatic animals. The jaws of adults were more flexible to hold struggling prey, and were well equipped to bite through the bony armor of hard-bodied animals like other placoderms.

Species

There have been either three or four different species of Dunkleosteus described so far.

D. terrelli

This is the largest, best known species of the genus. It has a rounded snout. D. terrelli's fossil remains are found in Famennian Late Devonian strata of the eastern United States and Europe.

D. marsaisi

D. marsaisi refers to the Dunkleosteus fossils from the Famennian Late Devonian strata of the Atlas Mountains in Morocco. It is very similar in size and form to D. terrelli, differing only in the snout, which, in D. marsaisi, is more narrow. Many researchers and authorities consider it a synonym of D. terrelli.^[6]

D. amblyodoratus

D. amblyodoratus is known from some fragmentary remains from Late Devonian strata of Kettle Point, Canada. The species name means "blunt spear," and refers to the way the nuchal and paranuchal plates in the back of the head form the shape of a blunted spearhead. Although it is known only from fragments, it is estimated to have been about 20 feet long in life.^[7]

D. raveri

D. raveri is a small, possibly 1-metre-long species 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, it is suggested that D. raveri may have given rise to D. terrelli. The species name commemorates Clarence Raver of Wakeman, Ohio, U.S., who discovered the concretion the holotype was found in.^[7]

History

Dunkleosteus was named in 1956 to honour David Dunkle, then curator of Vertebrate Paleontology at the Cleveland Museum of Natural History. The type species (D. terreli) was originally described in 1873 as a species of Dinichthys.

See also

Paleontology portal

• List of placoderms

References

1. ^ Ancient Fish With Killer Bite. Science News. May 19, 2009.
2. ^ Palmer, D., ed (1999). The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals. London: Marshall Editions. p. 33. ISBN 1-84028-152-9. 
3. ^ Monster fish crushed opposition with strongest bite ever. The Sydney Morning Herald. November 30, 2006.
4. ^ ^{a b} "Dunkleosteus Placodermi Devonian Armored Fish from Morocco". Fossil Archives. The Virtual Fossil Museum. http://www.fossilmuseum.net/Fossil_Galleries/Fish_Devonian/Dunkleosteous/Dunkleosteus.htm. Retrieved 2009-04-26. 
5. ^ ^{a b} Roy Britt, Robert (28 November 2006). "Prehistoric Fish Had Most Powerful Jaws". LiveScience. http://www.livescience.com/animals/061128_big_bite.html. Retrieved 2009-04-26. 
6. ^ Murray, A. M. The Palaeozoic, Mesozoic and Early Cenozoic fishes of Africa 25 DEC 2001
7. ^ ^{a b} Carr, R.K. & W.J. Hlavin, 2010: Two new species of Dunkleosteus

• Shape variation between arthrodire morphotypes indicates possible feeding niches by Philip S. L. Anderson, Journal of Vertebrate Paleontology volume 28, #4.

External links

• Introduction to the Placodermi: Extinct Armored Fishes with Jaws. Waggoner, Ben (2000). Retrieved Aug 1, 2005
• Dunkleosteus sp. Placodermi. The Virtual Fossil Museum (2002). Retrieved Aug 1, 2005

• Live Science: Prehistoric Fish Had Most Powerful Jaws
• Mikko's Phylogeny Archive

News articles

• MSNBC: Prehistoric fish packed a mean bite
• BBC: Ancient 'Jaws' had monster bite
• Courier Mail: Jaws of death
• CBC: Interview with Philip Anderson on Dunkleosteus Terrelli
• ABC News: Giant prehistoric fish packed quite a bite