Dunkleosteus

Dunkleosteus is an extinct genus of large arthrodire ("jointed-neck") fish that lived during the Late Devonian period, about 382–358 million years ago. It was a pelagic fish that lived in open waters and was one of the first vertebrate apex predators in any ecosystem. Fossils of Dunkleosteus have been found in the United States, Canada, Poland, Belgium, and Morocco.

Dunkleosteus includes ten species, with some being among the largest placoderms ("plate-skinned") ever known. The largest and best-known species is D. terrelli. Though its exact size is unclear, studies suggest that typical adults were about 3.4 metres (11 ft) long, with some exceptionally large individuals reaching up to 4.1 metres (13 ft). It has been suggested that Dunkleosteus could open and close its jaw quickly, possibly using suction like some modern fish, but these ideas are still being studied.

Discovery

Dunkleosteus fossils were first found in 1867 by Jay Terrell, a hotel owner who liked collecting fossils. He found them near Lake Erie in Sheffield Lake, Ohio, in the United States. Terrell gave his fossils to a scientist named John Strong Newberry, who in 1873 thought they all belonged to one new kind of fish called Dinichthys herzeri. But later, more fossils showed that there were actually different kinds of large fish in the Ohio Shale. Newberry named the more common one Dinichthys terrelli after Terrell. Sadly, most of Terrell’s original fossils were destroyed in a fire in Elyria, Ohio, in 1873.

Today, the largest collection of Dunkleosteus fossils is at the Cleveland Museum of Natural History. Other museums, like the American Museum of Natural History, the Smithsonian National Museum of Natural History, and the Natural History Museum in London, also have smaller collections. Many museums around the world display copies of the same famous specimen, CMNH 5768, which is kept at the Cleveland Museum of Natural History.

Taxonomy

Dunkleosteus was named in 1956 by Jean-Pierre Lehman to honor David Dunkle, a scientist who studied old fish fossils. The name Dunkleosteus means "Dunkle's bone" because of the strong bones found in its fossils.

Scientists first thought Dunkleosteus was part of another group called Dinichthys, but later studies showed they are different. Dunkleosteus belongs to a group called Dunkleosteoidea, while Dinichthys is in another group called Aspinothoracidi.

Species

Scientists have found fossils of at least ten different types of Dunkleosteus, but many of these might actually be the same type. The most well-known type is D. terrelli, which could grow as long as 10 meters (about 33 feet). Fossils of this type have been found in the United States and Europe.

Other types include D. raveri, a smaller species with big eyes, and D. tuderensis, found in Russia. Only a few types are widely accepted by scientists as true Dunkleosteus species.

Description

Size and anatomy

Dunkleosteus was covered in strong bone plates that formed a protective armor around its head and front body. These plates were thickest at the back of the head but thinner along the rest of the body. Unlike most modern fish, Dunkleosteus had both hard outer bone and a sponge-like inner layer.

We know most about the front part of Dunkleosteus from fossils, but the back part is less clear. Scientists often use fossils of smaller related fish to guess how the back may have looked. Estimates for the full length of Dunkleosteus terrelli vary widely, but most studies suggest typical adults were about 3.4 metres (11 feet) long, with some rare larger individuals possibly reaching 4.1 metres (13 feet).

The weight of these large fish was estimated to be between 950–1,200 kilograms (2,090–2,650 lb) for typical adults, and up to 1,764 kilograms (3,889 lb) for the largest individuals. Some scientists have suggested even larger sizes, but these estimates are less reliable.

One well-preserved fossil showed details of the fish's fins, suggesting they were more varied than previously thought. The spine of Dunkleosteus was likely very stiff, which may have helped it swim efficiently. Its pelvic fins were relatively small compared to its overall size.

Paleobiology

Dunkleosteus terrelli had a special way of opening its jaws very quickly, almost like modern fish that suck in prey. Scientists think it could also bite very hard, possibly harder than any other fish, living or extinct. However, some researchers suggest Dunkleosteus might have hunted by chasing and biting prey directly, rather than using suction.

Fossils show that Dunkleosteus may have eaten fast-swimming fish and often spat out undigested bones. It likely lived in deep water as an adult and shallower water when younger. Evidence suggests it might have been one of the first fish to fertilize eggs inside the body, like some sharks today. Studies of young Dunkleosteus show their jaws were strong enough to bite hard prey, unlike many younger land animals whose jaws are weaker.