Fossil Representative of Iowa
Brachiopod (common name)
A brachiopod is a marine invertebrate encased in two shells of unequal size. These shells are made of calcium carbonate secreted by the brachiopod. Also known as a lampshell, this solitary organism is sessile, meaning it anchors itself to the bottom surface or substrate of a body of water. Brachiopods first appeared about 525 million years ago, in the early part of the Cambrian period.
REPRESENTATIVE OF THE STATE
A devastating flood in the summer of 1993 covered millions of acres of Midwestern land. One result of the flood was that Iowa’s Coralville Reservoir spillway overflowed, eroding a deep channel and exposing limestone bedrock and Devonian-age ocean floor. This rare horizontal exposure, as well as the fossils embedded in the bedrock, became what is now known as the Devonian Fossil Gorge. Coralville Dam, just outside Iowa City, overflowed again in the summer of 2008, significantly widening the gorge. A visitor center now provides the public a glimpse back in time.
Iowa has not officially named a state fossil. But since brachiopod fossils are common in the gorge, they are therefore excellent representatives of Iowa’s geology. As the name of the gorge suggests, these specimens date from the Devonian period, making them approximately 360 to 415 million years old.
The word brachiopod was formed from the Latin bracchium orbrāchium, meaning "arm," and the Greek root πόδ (pod), which means "foot."
Brachiopods are benthic, which means they live on the bottom of the sea. Although they are enclosed in two symmetrical shells as are clams and oysters, they are not closely related to such similar-looking mollusks. Brachiopods are lophorates, which have unique rings of tentacles used as feeding organs. These organs are called lophophores and are used to filter the water around the brachiopod so it can feed on microscopic organisms and other food particles.
The shells of this organism are small, approximately 0.25 inch to 3 inches (0.6 to 7.5 cm) long. Some brachiopods have ridged shells and some have spiny shells that apparently evolved for protection. Modern brachiopods live for three to 30 years.
Depending on the species, brachiopods lie on the ocean bottom, cement themselves to it, or attach themselves with a long, thin appendage called a pedicle. The pedicle can act either as a tether or as a movable muscle. The larva of this organism, on the other hand, is free-floating. Upon metamorphosing into adults, brachiopods sink to the bottom, develop organs, may attach a pedicle to the surface, and become sessile. Brachiopods once lived in shallow waters, but have evolved to use very little energy and oxygen, allowing them to live in deep oceans.
Brachiopods were extremely abundant and diverse throughout the Paleozoic era; perhaps more than 10,000 species existed at that time. During the great extinction period called the Permo-Triassic extinction event, which took place at the end of the Paleozoic era approximately 250 million years ago, brachiopods, like many other species, decreased in number dramatically.
Killing nearly 90 percent of all organisms living at that time, this was the largest mass extinction event in history, larger even than the Cretaceous–Tertiary extinction event that is thought to have rendered the dinosaurs extinct. About 300 species of brachiopods survive today, however, living at the bottom of the oceans, mainly in very deep waters or in polar regions.
Brachiopod fossils can be found in Paleozoic limestone, dolomite, and shale throughout the present-day Midwestern and western United States, specifically Kansas, Ohio, Iowa, and Indiana. These fossils add to the evidence that seas once covered this area.
Although brachiopods live inside two hinged shells, they are not related to bivalves or other mollusks.
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|Author: World Trade Press|