13 Mayıs 2013 Pazartesi

Fossil Representative of American Samoa

Fossil Representative of American Samoa

Giant Clam (common name)
Tridacna giga 
(scientific name)
Tridacna is a genus of giant clam. Tridacna gigas is the largest species of bivalve known in the fossil record, as well as the largest living bivalve. Bivalves are marine mollusks that live inside two hinged shells. Giant clams are traditionally called pa’ua on a number of Pacific islands, and faisua in American Samoa.
Tridacna maxima and Tridacna squamosa are two giant clam species that are native to the waters around American Samoa. Because the territory is geologically young, it does not have abundant fossils, which probably explains why American Samoa does not have an official fossil. Giant clams have long been a favorite food among South Pacific islanders and their fossils are found in the seas in this part of the world. In American Samoa, giant clams often become part of fa'alavelave events (big gatherings for occasions like weddings and funerals), making these bivalves excellent representatives of the history and culture of this territory.
Tridacna gigas was described and named in 1758 by Swedish botanist and zoologist Carl Linnaeus, who is also known as the father of modern taxonomy. Tridacna maxima was named by German malacologist Peter Friedrich Röding (1767–1846) in 1798. Jean-Baptiste Pierre Antoine de Monet, Chevalier de la Marck (1744–1829), a French naturalist and early proponent of evolution, namedTridacna squamosa, the fluted giant clam, in 1819.
Like all bivalves, Tridacna species have two shells. The clam opens its shell by day to obtain the sunlight it needs for photosynthesis. It has plant-like cells called zooxanthellae in its tissues that need to be exposed to photosynthesize and produce food for the clam. In addition to photosynthesis, the giant clam nourishes itself by filter feeding to obtain zooplankton.
Giant clams live in warm, clear, shallow areas of the Pacific and Indian Oceans, such as reefs and shallow lagoons up to 60 feet (18 m) deep. Giant clam larvae swim freely in the ocean for about a week. Adult giant clams are sessile, which means they attach themselves to the ocean bottom and remain there for the rest of their lives.
Giant clams were once quite common in tropical seas. Fossil evidence exists showing that giant clams first appeared in the Eocene epoch, 34 to 55 million years ago, and modern Tridacnaevolved in the late Miocene epoch, approximately five to 11 million years ago. However, species of giant clams declined markedly in number about 125,000 years ago. This coincided with early humans leaving Africa, possibly in search of easier-to-find food sources, such as the motionless giant clams that inhabit shallow water. Due to overharvesting of giant clams for food and aquariums, Tridacna is one of the most endangered clams. It has become extinct in some areas where it was previously common.
In the past, giant clams were thought of as "killer clams" that could grasp or even eat a human. Reputable scientific publications, including the U.S. Navy Diving Manual, once mentioned deaths caused by these clams, as well as offering instructions for releasing oneself from their grasp. In fact, giant clams are neither aggressive nor particularly dangerous.
On the Solomon Islands, heavy arm rings were made of the shells ofTridacna or other clams. These arm rings, however, were not made from shells harvested from the ocean, but from fossilized shells found in the bush. Fossilized clamshell has also been used traditionally among Pacific islanders as currency, containers, and ceremonial objects. Tools and sculptures were carved from clamshell fossils.

Click to enlarge an image
State Prehistoric Creature
Giant Clams Are the Largest of All Clam Species
State Prehistoric Creature
Giant Clam or Tridacna Gigas

Euheterodonta incertae 
Species:T. gigas
Author: World Trade Press

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