Fossils include the remains or traces of prehistoric plants and animals preserved in rock or sediments of the earth’s crust. Fossils provide a record of former life, information that is vital in interpreting ancient environments, and a means of dating the rock layers.
West Virginia has a rich fossil record. Fossils are found in coal mines and excavations, including road cuts. Plant fossils are commonly found in shales that overlie coal beds. These coal beds are often exposed along highways in the southern, northwestern, and north-central parts of the state, including Interstates 68, 79, and 77. Fossil seashells are more likely to be found in the eastern counties bordering Virginia and Maryland.
Virtually all the bedrock of the state is from the geologic period known as the Paleozoic Era (570 to 240 million years ago), created from sediment laid down in ancient seas. Invertebrate fossils are abundant in these marine rock strata. The more common types include brachiopods, bryozoans, crinoids, corals, and trilobites. Molluscan remains including snails, clams, and squid-like animals called cephalopods are also common in some marine shales and limestones.
Early Paleozoic rocks outcrop at the surface only in the Eastern Panhandle and along the Virginia border in Mercer and Monroe counties. The oldest known fossils occur in the Antietam Formation in Jefferson County. This sandstone formation is from the early Cambrian Period, early in the Paleozoic Era, and contains abundant vertical burrows and sparse trilobites, gastropods, and brachiopods. Aquatic plants (algae) were common in shallow seas and formed wavy, laminated, fine-grained limestone deposits called stromatolites. Marine invertebrates become increasingly more diverse in limestones and shales of the Ordovician Period, which followed the Cambrian. Brachiopods and bryozoans are especially common. Brachiopods superficially resembled clams. Bryozoans were tiny bottom-dwelling animals that built moss-like, twig-like, or fan-shaped colonies commonly several centimeters or more in length. These calcareous colonies were perforated with tiny pores less than one millimeter in diameter, each of which housed a filter-feeding bryozoan.
During the Silurian and Devonian periods, later in the Paleozoic Era, West Virginia was covered most of the time by the sea. The earliest known land plants from West Virginia occur as fossils in the eastern counties in Late Devonian strata. They include leaves from large trees and two-meter high plants called Rhacophyton.
The Mississippian Period followed the Devonian, still part of the Paleozoic Era. Mississippian rocks are mostly marine strata and include abundant remains of crinoids and blastoids. These animals resemble flowers and were attached to the sea floor by a flexible ‘‘stem’’ made up of disc-like plates that resemble lifesavers. Their flower-like heads contained slender ciliated appendages used for filtering suspended organic materials from the surrounding seawater. Strata of Mississippian age outcrop in the southeastern part of the state, and are extensive in Greenbrier County where they have been quarried for limestone.
The Pennsylvanian Period followed the Mississippian. Pennsylvanian shales associated with coal beds contain abundant plant fossils. They are represented by roots, trunks, branches, and leaves. Lycopod or spore-producing trees including sigillaria and lepidodendron were especially common and developed in close association with peat swamps. The diamond or spindle-shaped pattern of lepidodendron is sometimes mistaken for fossilized snake skins. Ferns are also prevalent in some strata. ‘‘Kettle bottoms’’ are petrified mud casts of a fossil tree trunk extending up into the roof of a coal seam, resembling the bottom of a kettle or pot when seen from below. Kettle bottoms may fall into the mine without warning, a dangerous hazard for miners.
Vertebrate remains from Late Paleozoic strata include fish, amphibians, and reptiles. Fossils include teeth, scales, spines, bones, and coprolites (fecal material). Of particular interest are xenacanths, which were freshwater sharks. Amphibians also are represented by trackways, traces of ancient passage preserved in time in the geologic records.
This Article was written by Ronald Martino
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Cite This Article
Martino, Ronald "Fossils." e-WV: The West Virginia Encyclopedia. 28 February 2011. Web. 27 November 2024.
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