28 Şubat 2013 Perşembe

State Fossil of Ohio

State Fossil of Ohio

Trilobite (common name of class)
(scientific name of genus)
Isotelus is a genus of trilobite that lived approximately 430 to 500 million years ago, during the Ordovician period of the Paleozoic era. Trilobites are extinct marine arthropods, a phylum that includes modern crabs, horseshoe crabs, lobsters, scorpions, centipedes, spiders, and insects. Isotelus lived at the bottom of the seas that once covered much of present-day North America.
Because trilobites shed their exoskeletons several times in a lifetime, and because these hard outer shells fossilized easily, trilobite fossils are fairly abundant in what is now the northeastern United States, southern Ontario, southern Quebec, and northwestern Manitoba. The largest known species of trilobite is Isotelus rex.
Although many are fragmented, Isotelus specimens are fairly common in exposed rock throughout Ohio. During the Ordovician period, a warm, shallow sea covered parts of present-day North America, including what is now the state of Ohio. One of the largest complete trilobites ever found was an Isotelus specimen discovered at Huffman Dam in northeast Dayton, Ohio. Following a proposal from two Dayton-area elementary school classes, the trilobite genusIsotelus was designated the official fossil of Ohio on June 20, 1985.
The word trilobite means "three-lobed" and comes from the Greek words τρία (tria) and λοβός (lobos). This refers to the three general divisions of a trilobite’s body. The word "arthropod" comes from the Greek words αρθρον (arthron), meaning "joint," and ποδός (podos), meaning "foot," referring to an arthropod’s jointed appendages.
Isotelus, the name of Ohio's genus of trilobite, comes from Greek ίσος (isos), meaning equal, and τέλος (telos) meaning end or extremity. American zoologist and geologist James Ellsworth DeKay named Isotelus gigas in 1824. In 1838, John Locke of the Geological Survey of Ohio named another species of this genus Isotelus maximus. Both species were named for their large size.
Like all arthropods, Isotelus had an exoskeleton, a segmented body, and jointed appendages. Isotelus had a pair of legs on every segment. It had a semicircular head and tail shields. This predatory trilobite crawled along the muddy seafloor, hunting smaller organisms. It grew up to 28 inches (71 cm) in length.
Trilobites lived throughout the Paleozoic age, first appearing early in the Cambrian period. Approximately 251 million years ago, a mass extinction event called the Permian–Triassic Extinction Event took place. This event occurred at the end of the Permian period of the Paleozoic era and the beginning of the Triassic period of the Mesozoic era, wiping out nearly 96 percent of all marine species and almost 70 percent of all terrestrial vertebrates living at the time. It is not known exactly what caused this event, but most theories include some form of catastrophe having a global impact.
In 1919, during construction of the Huffman Dam outside Dayton, Ohio, an Isotelus specimen measuring 14.5 inches (36.8 cm) long by 10.5 inches (26.7 cm) wide was discovered. This large specimen is now on permanent display at the Smithsonian’s National Museum of Natural History in Washington, DC. Large specimens have since been found in other eastern states.
The largest complete trilobite ever found is an Isotelus rex specimen 28 inches (72 cm) long and 16 inches (40 cm) wide. This specimen was discovered in 1999 in Churchill, Manitoba, and is now displayed at the Manitoba Museum in Winnipeg.

Click to enlarge an image
State Prehistoric Creature
State Prehistoric Creature
Fossil Trilobite Exoskeletons 
State Prehistoric Creature
Polished Fossil Trilobite

Author: World Trade Press

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