21 Mart 2013 Perşembe

State Fossil of Wisconsin

State Fossil of Wisconsin

Trilobite (common name)
Calymene celebra 
(scientific name)
Calymene celebra is a species of trilobite that lived during the Silurian and late Ordovician periods of the Paleozoic age, approximately 410 to 460 million years ago. Trilobites are extinct marine arthropods, a phylum that includes modern crabs, horseshoe crabs, lobsters, scorpions, centipedes, spiders, and insects.
Calymene celebra inhabited the reefs of the warm, shallow sea that covered much of present-day North America during the Paleozoic era. Because trilobites shed their exoskeletons several times in a lifetime, and because these hard outer shells fossilized easily, trilobite fossils are now fairly abundant in North America.
Well-formed specimens of Calymene celebra can be found throughout the state of Wisconsin, especially in limestone and dolomite deposits in the southern part of the state. Although quite rare, specimens including the organism’s antennae and legs can sometimes be found. On April 2, 1986, upon a proposal from the Wisconsin Geological Society, this trilobite was designated the official state fossil.
The genus name Calymene is derived from the Greek word κάλυμμα (kaluma). This word means "cover" and apparently alludes to the organism’s exoskeleton, as well as its ability to roll up into a ball for protection.
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.
Every arthropod had an exoskeleton, a segmented body, and jointed appendages, and Calymene celebra is no exception. This trilobite crawled along the seafloor and fed on other marine organisms. Normally one to two inches (2.5 to 5 cm) in length, the largest complete Calymene celebra fossil specimen ever found is 14 inches (35.6 cm) long.
Trilobites were the first organisms to develop holochroal eyes, compound eyes with many tiny lenses. This distinctive trilobite feature provides paleontologists evidence of eye evolution. Trilobites lived throughout the Paleozoic era, first appearing on earth early in the Cambrian period over 530 million years ago.
Approximately 251 million years ago, a mass extinction event referred to as the Permian–Triassic extinction event occurred. The most severe extinction in earth’s history, this event took place at the transition from the Permian period of the Paleozoic era to the Triassic period of the Mesozoic era. It wiped out nearly 96 percent of all marine species and almost 70 percent of all terrestrial vertebrates living at the time. Trilobites as a class, includingCalymene celebra, ceased to exist at that time. It is not known exactly what caused this event, but most theories include some form of catastrophe that had a global impact.
Self-educated naturalist and engineer Increase Allen Lapham collected the first Calymene fossils in the Wisconsin Territory in the 1830s. Latham’s extensive natural history collection, including fossils, shells, minerals, meteorites, and Indian relics, is now owned by the University of Wisconsin.
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
Trilobites Embedded in Rock
State Prehistoric Creature
Polished Trilobite Specimen 

Author: World Trade Press

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