Jump to content

Shark tooth: Difference between revisions

From Wikipedia, the free encyclopedia
Content deleted Content added
Posching (talk | contribs)
→‎External links: Anfügen eines Liks zu einer Literaturdatenbank
Line 140: Line 140:
===External links===
===External links===
* [http://www.bishopmuseum.org/exhibits/pastExhibits/1997/treasures/html/WEAPON.html A weapon of tiger-shark teeth on carved koa wood], at the [[Bishop Museum]].
* [http://www.bishopmuseum.org/exhibits/pastExhibits/1997/treasures/html/WEAPON.html A weapon of tiger-shark teeth on carved koa wood], at the [[Bishop Museum]].
* --[[User:Posching|Posching]] ([[User talk:Posching|talk]]) 10:13, 14 July 2009 (UTC)[http://www.shark-references.com www.shark-references.com: Database of bibliography of living/fossil sharks and rays (Chondrichtyes: Selachii) with more than 3.000 listed papers and a lot of downloadlinks]


{{Shark nav}}
{{Shark nav}}

Revision as of 10:13, 14 July 2009

For disambiguation see Shark teeth (disambiguation).


Anatomy of a shark's tooth

Shark teeth are relics of shark evolution and biology. Shark skeletons are composed entirely of cartilage. Often the only parts of the shark to survive as fossils are teeth. Fossil shark teeth have been dated back hundreds of millions of years. The most ancient types of sharks date back to 450 million years ago during the Late Ordovician period, and they are mostly known from their fossilized teeth. The most common, however, are from the Cenozoic Era (65 million years ago).

Sharks and rays both have a polyphyodont dentition, in which old teeth are shed continually throughout the fish's lifetime, and new ones are rotated into place on a conveyer belt-like structure.[1] Shark teeth develop along the inner surface of the jaw cartilage, and are attached to the dental membrane. When the tooth forms in the gum tissue, the crown cap develops first, followed by the root.[1]

Shark teeth are commonly found fossils for two reasons. Sharks continually shed their teeth, and some Carchariniformes can shed approximately 35,000 teeth in a lifetime. Secondly, the environment in which the teeth are deposited after falling from a shark's jaws has a high concentration of phosphate.

Overview

Reconstructed Carcharoles megalodon jaws on display at the American Museum of Natural History.

A shark can have hundreds of teeth in its jaw. Sharks, as well as other Chondrichthyes, have the ability to replace their teeth if they become damaged during feeding or fall out due to natural causes. Many icthyologists have suggested that sharks can lose tens of thousands of teeth within the span of a few years.[2]

The teeth of sharks are not attached to the jaw, but embedded in the flesh, and in many species are constantly replaced throughout the shark's life. When they lose a working tooth it will be replaced by the next tooth behind it. All sharks have multiple rows of teeth along the edges of their upper and lower jaws. New teeth grow continuously in a groove just inside the mouth and move forward from inside the mouth on a "conveyor belt" formed by the skin in which they are anchored. Typically a shark has two to three working rows of teeth with 20 to 30 teeth in each row, e.g. a whale shark has about 300 teeth in each row.[2] The replacement rate has not been measured in most sharks but normally the teeth seem to be replaced every two weeks. The lemon shark replaces its teeth every 8–10 days, and the great white shark replaces its teeth about every 100 days for young sharks and about every 230 days for old sharks.[3] Most sharks shed individual teeth, but e.g. the cookiecutter shark sheds the whole lower jaw at once. The lower teeth are primarily used for holding prey, while the upper ones are used for cutting into it. The teeth range from thin, needle-like teeth for gripping fish to large, flat teeth adapted for crushing shellfish.

Shark teeth are formed by the same mechanism as the scales on sharks' skin.[citation needed]

History of discovery

The oldest known records of fossilized shark teeth being found, are by Pliny the Elder, in which be believed that these triangular objects fell from the sky during lunar eclipses. Later on, during the Middle Ages, the term Glossopetrae (tongue-stones) was coined. Shark teeth, or glossopetrae, were commonly thought to be able to be a remedy or cure for various poisons and toxins, including helping in the treatment of snake bites. Due to this ingrained belief, many noblemen and royalty wore shark tooth pendants or kept glossopetrae in their pockets as good-luck charms. This may have led to the modern-day practice of wearing shark tooth necklaces.

Modern shark teeth

Modern shark teeth are shark teeth that have not yet fossilized in one way or another.

Great white shark

The modern-day Great White shark is a protected species under CITES, and has been protected for over 10 years. The Great White was given Appendix II status, which means a permit is required to be able to trade its parts, however teeth that are on the market are still legal to own. Due to the protected status, large, modern teeth can reach prices over $800–1000 USD.

Fossil shark teeth

Megalodon teeth

A group of Otodus obliquus teeth in the original matrix.
Size comparison between a Megalodon shark tooth and two teeth from a great white

Carcharocles megalodon teeth are among the most sought after types of shark teeth in the world. These teeth are in extremely high demand by collectors and private investors, and they can fetch steep prices. This shark lived during the Miocene and Pliocene eras, roughly about 16 to 1.5 million years ago. Its teeth on average range between 1.5 to 6.5 inch in length. The largest examples can reach a length of more than 7 inches. These huge teeth indicate that the Megalodon could grow up to more than 16 m (52.5 ft) long, growing bigger than the largest fish alive in the world today, the whale shark.

Large numbers of Megalodon teeth have been discovered across both coasts of the United States. The most plentiful locations within the U.S. are the Carolinas, Georgia, and parts of Florida and Virginia.

These large sharks disappeared relatively close to the rise of modern man, however, there have been many unconfirmed reports of large carnivorous fish resembling Megalodon sharks in recent times. Megalodon teeth have been discovered that some may argue date as recently as 10,000 to 15,000 years ago. This claim is based on the discovery of two teeth by the HMS Challenger scientific expedition. These teeth were dated by estimating the amount of time it took for manganese to accumulate on them, although it is quite possible the teeth were fossilized before being encrusted.

Transitional teeth

Identifying shark teeth is tedious work, especially with all of the damaged, worn, and different teeth. It is even more difficult because of the so-called "In-between teeth". These are teeth that are from a shark species that was evolving into another, different species. An example of this can be seen with Carcharocles auriculatus teeth that were in the state of evolving into Carcharocles angustidens. These are teeth that are no longer auriculatus, but not yet angustidens either.

Great White/Mako transitional teeth

The most common and most referred to transitional shark teeth are the ones coming from what is believed by some to be an unusual form of great white shark. Great white shark transitional teeth are often characterized for their wide crowns. These teeth can also be identified by the way the serrations fade, being more pronounced near the root, and disappearing close to the tip of the tooth.

Many paleontologists now believe that these transitional teeth represent the evolutionary path between Isurus hastalis and the Great White shark. The evolutionary history of the great white shark and its relation to Megalodon are hotly debated.

Because of their transitional state, these teeth are rare. These teeth are prized by collectors, hobbyists, and museums.

Shark-tooth tools

Gilbertese weapons edged with shark teeth.

In Oceania and America, shark teeth were commonly used for tools, especially weapons such as clubs and daggers, but also to carve wood and as tools for food preparation. For example, various weapons edged with shark teeth were used in Hawaii (see example here[4]), with some types reserved for royalty.[5] The Guaitaca (Weittaka) of coastal Brazil tipped their arrows with shark teeth,[6] and in the Cahokia mounds of the upper Mississippi River valley a thousand kilometers from the ocean, the remains of sharktooth-edged weapons have been found, as well as chert replicas of shark teeth.[7] It is reported that the rongorongo tablets of Easter Island were first shaped and then inscribed using a hafted shark tooth.[8]

Collecting shark teeth

Three collectors searching for fossil shark teeth in Lee Creek mine phosphate pit.

Shark teeth cannot be collected from any type of rock. Any fossils, including fossil shark teeth, are preserved in sedimentary rocks. Shark teeth are most commonly found between Upper Cretaceous and Tertiary periods.[2]

Field collecting

Fossilized shark teeth can often be found in or near river bed banks, sand pits, and beaches. The most common and simplest way is to walk along the site and collect. Many people prefer to use a shovel and sieve. Many collectors use fork-like garden tools to excavate sand.

Many sites provide hard, solid teeth, that are only washed and dried.[2] These teeth are typically worn, because they were frequently moved and redeposited in different areas repeatedly before settling down.[2] Other locations, however, yield perfect teeth that were hardly moved during the ages. these teeth are typically fragile, and great care should be taken while excavating them.[2]

A popular technique for collecting shark teeth is too simply scan the fossiliferous area, looking for glints of sun off of enamel.

Phosphate mines

Phosphate pits, mostly comprised of fossils bones and teeth, or kaoline pits, are ideal places to look for fossil shark teeth. One of the most notable phosphate mines is in Central Florida, Polk County, and is known as Bone Valley.

Deep-Sea dredging

Near New Caledonia, up until the practice was banned, fishermen and commercial vessels used to dredge the sea floor for megalodon teeth.

Well known fossil hunting areas:

  • Venice Beach, Florida (Sharks Tooth Festival every April)
  • Lee Creek Mine, PCS Phosphate Pit, Aurora, North Carolina
  • Bone Valley Phosphate Pit, Lower Florida
  • Sharktooth Hill, Bakersfield, California[9]
  • Calvert Formation, Calvert Cliffs, Maryland
  • Ouled Abdoun Basin, Morocco
  • Atlas Mountains Phosphate Pit, Khouribga, Morocco
  • Hawthorne Formation, South Carolina, Florida, Georgia
  • Huarra Formation, Antofagasta, Chile

Buying teeth

There is a small, but established shark tooth trade, and it is up to the collector if he/she wants to 'complete' their collection by buying a few fossils.

Many high quality fossils can be found online, and many are often affordable. As well as on the internet, shark teeth may be procured from Rock and Mineral shows, such as the annual Tucson Gem & Mineral Show, and other, smaller, rock shops.

The prices of shark teeth depend upon the overall quality of the tooth. There is no definite price for a shark tooth, as the market is based on supply-and-demand. Another way of obtaining shark teeth is to "swap" finds with others at rock shops of mineral shows/conventions.

Identification

The most often method of shark tooth identification, is to procure a book on sharks teeth and attempt to identify it yourself. Many expert collectors tend to identify their teeth this way, yet others prefer to seek experts willing to help them identify their teeth.

Many identified shark teeth are transitional species. Because sharks lose tens of thousands of teeth in their lifetime, their teeth vary greatly, because they are constantly evolving new changes in their feeding style, and their teeth.

See also

Template:Sharksportal

References

  1. ^ a b Welton, Bruce J., Ph.D. The Collector's Guide to Fossil Sharks and Rays from the Cretaceous of Texas. pp. 12-28.
  2. ^ a b c d e f Hennemann RM. Sharks & Rays: Elasmobranch Guide of the World. IKAN-Unterwasserarchiv, Frankfurt, Germany 2001:266-269.
  3. ^ "Teeth of the Skin". Elasmo-research.org. Retrieved 2008-11-27.
  4. ^ "Treasures of Hawai'i : Shark Tooth Weapon". Bishopmuseum.org. Retrieved 2008-11-27.
  5. ^ Anthony Meyer (1995) Oceanic Art, v. 2, p. 579.
  6. ^ Alfred Metraux, Alfred (1946) Handbook of South American Indians, v. 1, p. 522, "The Guaitaca"
  7. ^ Greg Perino, c. 1950, Cahokia Brought to Life, pp 66-67
  8. ^ Alfred Métraux (1940), "Ethnology of Easter Island". Bernice P. Bishop Museum Bulletin (Honolulu: Bernice P. Bishop Museum Press) 160:404
  9. ^ David Perlman (Saturday June 6 2009). "Ancient sea life thrived in Central Valley". San Francisco Chronicle. {{cite web}}: Check date values in: |date= (help)
  • Campbell, Sid (2006). "Shark-Tooth Weapons". Warrior Arts and Weapons of Ancient Hawaii. Berkeley, Calif: Blue Snake Books. ISBN 1-58394-160-6. OCLC 65400291.
  • Castro, Jose (1983). The Sharks of North American Waters. College Station: Texas A&M University Press. ISBN 0-89096-143-3.
  • Hennemann RM. Sharks & Rays: Elasmobranch Guide of the World. IKAN-Unterwasserarchiv, Frankfurt, Germany 2001:266-269.
  • Stevens, John D. (1987). Sharks. New York: NY Facts on File Publications. ISBN 0-8160-1800-6.