The Ordovician is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period 485.4 million years ago (Mya) to the start of the Silurian Period 443.8 Mya.
The Silurian is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at 443.8 million years ago (Mya), to the beginning of the Devonian Period, 419.2 Mya. The Silurian is the shortest period of the Paleozoic Era. As with other geologic periods, the rock beds that define the period's start and end are well identified, but the exact dates are uncertain by a few million years. The base of the Silurian is set at a series of major Ordovician–Silurian extinction events when up to 60% of marine genera were wiped out.
Hallopora is an extinct genus of bryozoans of the family Halloporidae, first identified from the Lower Silurian period. They can be found in Ohio, Indiana, and Kentucky of the Midwestern United States, commonly in the Ordovician Kope Formation.
Carbonate hardgrounds are surfaces of synsedimentarily cemented carbonate layers that have been exposed on the seafloor. A hardground is essentially, then, a lithified seafloor. Ancient hardgrounds are found in limestone sequences and distinguished from later-lithified sediments by evidence of exposure to normal marine waters. This evidence can consist of encrusting marine organisms, borings of organisms produced through bioerosion, early marine calcite cements, or extensive surfaces mineralized by iron oxides or calcium phosphates. Modern hardgrounds are usually detected by sounding in shallow water or through remote sensing techniques like side-scan sonar.
Constellaria is an extinct genus of bryozoan from the Middle Ordovician to Early Silurian from North America, Asia and Europe. These branching coral-like bryozoans formed bushy colonies 10-15 mm across on the seabed. The fairly thick branches were erect, often compressed in one direction, and covered with distinctive tiny, star-shaped mounds called maculae or monticules. Feeding zoids were located along the rays of the stars. The maculae probably formed "chimneys" for the expulsion of exhalant feeding currents from the surface of a colony, after water had been filtered to obtain food for the organisms.
The Brassfield Formation, named by A.F. Foerste in 1906, is a limestone and dolomite formation exposed in Arkansas, Ohio, Kentucky, Indiana, Tennessee and West Virginia in the United States. It is Early Silurian in age and well known for its abundant echinoderms, corals and stromatoporoids. In Ohio, where the unit has escaped dolomitization, the Brassfield is an encrinite biosparite with numerous crinoid species.
Paleontology in Kentucky refers to paleontological research occurring within or conducted by people from the U.S. state of Kentucky.
Paleontology in Indiana refers to paleontological research occurring within or conducted by people from the U.S. state of Indiana. Indiana's fossil record stretches all the way back to the Precambrian, when the state was inhabited by microbes. More complex organisms came to inhabit the state during the early Paleozoic era. At that time the state was covered by a warm shallow sea that would come to be inhabited by creatures like brachiopods, bryozoans, cephalopods, crinoids, and trilobites. During the Silurian period the state was home to significant reef systems. Indiana became a more terrestrial environment during the Carboniferous, as an expansive river system formed richly vegetated deltas where amphibians lived. There is a gap in the local rock record from the Permian through the Mesozoic. Likewise, little is known about the early to middle Cenozoic era. During the Ice Age however, the state was subject to glacial activity, and home to creatures like short-faced bears, camels, mammoths, and mastodons. After humans came to inhabit the state, Native Americans interpreted the fossil proboscidean remains preserved near Devil's Lake as the bones of water monsters. After the advent of formal scientific investigation one paleontological survey determined that the state was home to nearly 150 different kinds of prehistoric plants.
Paleontology in Virginia refers to paleontological research occurring within or conducted by people from the U.S. state of Virginia. The geologic column in Virginia spans from the Cambrian to the Quaternary. During the early part of the Paleozoic, Virginia was covered by a warm shallow sea. This sea would come to be inhabited by creatures like brachiopods, bryozoans, corals, and nautiloids. The state was briefly out of the sea during the Ordovician, but by the Silurian it was once again submerged. During this second period of inundation the state was home to brachiopods, trilobites and entire reef systems. During the mid-to-late Carboniferous the state gradually became a swampy environment.
Paleontology in Tennessee refers to paleontological research occurring within or conducted by people from the U.S. state of Tennessee. During the early part of the Paleozoic era, Tennessee was covered by a warm, shallow sea. This sea was home to brachiopods, bryozoans, cephalopods, corals, and trilobites. Tennessee is one of the best sources of Early Devonian fossils in North America. During the mid-to-late Carboniferous, the state became a swampy environment, home to a rich variety of plants including ferns and scale trees. A gap in the local rock record spans from the Permian through the Jurassic. During the Cretaceous, the western part of the state was submerged by seawater. The local waters were home to more fossil gastropods than are known from anywhere else in the world. Mosasaurs and sea turtles also inhabited these waters. On land the state was home to dinosaurs. Western Tennessee was still under the sea during the early part of the Cenozoic. Terrestrial portions of the state were swampy. Climate cooled until the Ice Age, when the state was home to Camelops, horses, mammoths, mastodons, and giant ground sloths. The local Yuchi people told myths of giant lizard monsters that may have been inspired by fossils either local or encountered elsewhere. In 1920, after local fossils became a subject of formal scientific study, a significant discovery of a variety of Pleistocene creatures was made near Nashville. The Cretaceous bivalve Pterotrigonia thoracica is the Tennessee state fossil.
Paleontology in New Hampshire refers to paleontological research occurring within or conducted by people from the U.S. state of New Hampshire. Fossils are very rare in New Hampshire because so much of the state's geology is highly metamorphic. The state's complicated geologic history has made dating its rocks and the fossils they contain "a difficult task." The state's Devonian rocks are especially metamorphosed, yet its Mississippian rocks formed too recently to have been subject to the same metamorphism. Nevertheless, despite the geologic complications some fossils have been discovered in the state.
Paleontology in Wisconsin refers to paleontological research occurring within or conducted by people from the U.S. state of Wisconsin. The state has fossils from the Precambrian, much of the Paleozoic, and the later part of the Cenozoic. Most of the Paleozoic rocks are marine in origin. Because of the thick blanket of Pleistocene glacial sediment that covers the rock strata in most of the state, Wisconsin’s fossil record is relatively sparse. In spite of this, certain Wisconsin paleontological occurrences provide exceptional insights concerning the history and diversity of life on Earth.
Paleontology in Minnesota refers to paleontological research occurring within or conducted by people from the U.S. state of Minnesota. The geologic record of Minnesota spans from Precambrian to recent with the exceptions of major gaps including the Silurian period, the interval from the Middle to Upper Devonian to the Cretaceous, and the Cenozoic. During the Precambrian, Minnesota was covered by an ocean where local bacteria ended up forming banded iron formations and stromatolites. During the early part of the Paleozoic era southern Minnesota was covered by a shallow tropical sea that would come to be home to creatures like brachiopods, bryozoans, massive cephalopods, corals, crinoids, graptolites, and trilobites. The sea withdrew from the state during the Silurian, but returned during the Devonian. However, the rest of the Paleozoic is missing from the local rock record. The Triassic is also missing from the local rock record and Jurassic deposits, while present, lack fossils. Another sea entered the state during the Cretaceous period, this one inhabited by creatures like ammonites and sawfish. Duckbilled dinosaurs roamed the land. The Paleogene and Neogene periods of the ensuing Cenozoic era are also missing from the local rock record, but during the Ice Age evidence points to glacial activity in the state. Woolly mammoths, mastodons, and musk oxen inhabited Minnesota at the time. Local Native Americans interpreted such remains as the bones of the water monster Unktehi. They also told myths about thunder birds that may have been based on Ice Age bird fossils. By the early 19th century, the state's fossil had already attracted the attention of formally trained scientists. Early research included the Cretaceous plant discoveries made by Leo Lesquereux.
The Maquoketa Formation is a geologic formation in Illinois, Indiana. Iowa, Kansas, Minnesota, Missouri, and Wisconsin. It preserves mollusk, coral, brachiopod and graptolite fossils dating back to the Darriwilian to Hirnantian stages of the Ordovician period.
The Waukesha Biota is an important fossil site located in Waukesha and Franklin, Milwaukee County within the state of Wisconsin. This biota is preserved in certain strata within the Brandon Bridge Formation, which dates to the early Silurian period. It is known for the exceptional preservation of soft-bodied organisms, including many species found nowhere else in rocks of similar age. The site's discovery was announced in 1985, leading to a plethora of discoveries. This biota is one of the few well studied Lagerstättes from the Silurian, making it important in our understanding of the period's biodiversity. Some of the species are not easily classified into known animal groups, showing that much research remains to be done on this site. Other taxa that are normally common in Silurian deposits are rare here, but trilobites are quite common.
Homotrypa is an extinct genus of bryozoans from the Ordovician and Silurian periods, known from fossils found in the United States. Its colonies are branch-like and have small monticules made of groups of three or four larger zooecia slightly protruding out from the main surface of the colony. In cross section, the zooecia are erect in axis and gently curve toward the surface of the colony.
Moyerella is an extinct genus of bryozoan of the family Arthrostylidae, known from the Upper Ordovician and Lower Silurian periods. Its colonies are branching or segmented, generally articulated (jointed). Its autozooecia are short tubes that appear triangular in cross section within the endozone, bending abruptly when reaching the exozone. The autozooecial apertures are round and aligned into diagonal rows, and paired heterozooecia occur between the autozooecial apertures.
Ptilodictya is an extinct genus of bryozoan of the family Ptilodictyidae. It formed bifoliate branched colonies, with branches ranging from under 1 to 3 mm wide. Colonies' autozooecia are rectangular and autozooecial apertures are in the shape of rounded rectangles.
Lichenalia is an extinct genus of cystoporate bryozoan belonging to the family Rhinoporidae. It is known from the Upper Ordovician to the Middle Silurian periods, which spanned from approximately 460 to 430 million years ago. The genus had a cosmopolitan distribution, with fossil specimens found in various regions of the world, including North America, Europe, and Asia.
