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 third and shortest period of the Paleozoic Era, and the third of twelve periods of the Phanerozoic Eon. 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.
In the geological timescale, the Llandovery Epoch occurred at the beginning of the Silurian Period. The Llandoverian Epoch follows the massive Ordovician-Silurian extinction events, which led to a large decrease in biodiversity and an opening up of ecosystems.
Soldiers' Home Reef, also known as Rocky Point, National Military Asylum Reef, or Veterans' Hill is a fossilized coral reef rock formation in Milwaukee, Wisconsin. The reef formation was discovered by geologist Increase A. Lapham in the 1830s. It and other fossilized coral reefs that he discovered were the first geological reef formations described in North America, and are among the first described in the world. This reef was declared a National Historic Landmark in 1993.
Diplichnites are arthropod trackways with two parallel rows of blunt to elongate, closely spaced tracks oriented approximately perpendicularly to the mid-line of the trackway. The term is more often used for the ichnofossils of this description; however, similar trackways from recent arthropods are sometimes given this name as well.
Euthycarcinoidea are an enigmatic group of extinct, possibly amphibious arthropods that ranged from Cambrian to Triassic times. Fossils are known from Europe, North America, Argentina, Australia, and Antarctica.
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 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 Illinois refers to paleontological research occurring within or conducted by people from the U.S. state of Illinois. Scientists have found that Illinois was covered by a sea during the Paleozoic Era. Over time this sea was inhabited by animals including brachiopods, clams, corals, crinoids, sea snails, sponges, and trilobites.
Paleontology in Missouri refers to paleontological research occurring within or conducted by people from the U.S. state of Missouri. The geologic column of Missouri spans all of geologic history from the Precambrian to present with the exception of the Permian, Triassic, and Jurassic. Brachiopods are probably the most common fossils in Missouri.
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.
Paleontology in Texas refers to paleontological research occurring within or conducted by people from the U.S. state of Texas. Author Marian Murray has said that "Texas is as big for fossils as it is for everything else." Some of the most important fossil finds in United States history have come from Texas. Fossils can be found throughout most of the state. The fossil record of Texas spans almost the entire geologic column from Precambrian to Pleistocene. Shark teeth are probably the state's most common fossil. During the early Paleozoic era Texas was covered by a sea that would later be home to creatures like brachiopods, cephalopods, graptolites, and trilobites. Little is known about the state's Devonian and early Carboniferous life. Evidence indicates that during the late Carboniferous the state was home to marine life, land plants and early reptiles. During the Permian, the seas largely shrank away, but nevertheless coral reefs formed in the state. The rest of Texas was a coastal plain inhabited by early relatives of mammals like Dimetrodon and Edaphosaurus. During the Triassic, a great river system formed in the state that was inhabited by crocodile-like phytosaurs. Little is known about Jurassic Texas, but there are fossil aquatic invertebrates of this age like ammonites in the state. During the Early Cretaceous local large sauropods and theropods left a great abundance of footprints. Later in the Cretaceous, the state was covered by the Western Interior Seaway and home to creatures like mosasaurs, plesiosaurs, and few icthyosaurs. Early Cenozoic Texas still contained areas covered in seawater where invertebrates and sharks lived. On land the state would come to be home to creatures like glyptodonts, mammoths, mastodons, saber-toothed cats, giant ground sloths, titanotheres, uintatheres, and dire wolves. Archaeological evidence suggests that local Native Americans knew about local fossils. Formally trained scientists were already investigating the state's fossils by the late 1800s. In 1938, a major dinosaur footprint find occurred near Glen Rose. Pleurocoelus was the Texas state dinosaur from 1997 to 2009, when it was replaced by Paluxysaurus jonesi after the Texan fossils once referred to the former species were reclassified to a new genus.
The Milwaukee Formation is a fossil-bearing geological formation of Middle Devonian age in Milwaukee County, Wisconsin. It stands out for the exceptional diversity of its fossil biota. Included are many kinds of marine protists, invertebrates, and fishes, as well as early trees and giant fungi.
The Brandon Bridge Formation is a geologic formation in Wisconsin. It preserves fossils dating back to the Silurian period, including those of graptolites, conodonts and Parioscorpio.
The Attawapiskat Formation is a geologic formation in Ontario. It preserves fossils dating back to the Silurian period.
The Sinnipee Group is a geological group in Wisconsin. It consists primarily of sedimentary carbonate rocks. Primarily made of dolomite, it also has limestone as a secondary component and can even have shale imbedded with it. It was formed in the Ordovician period and has three rock members: Galena, Decorah, and Platteville formations.
Parioscorpio is an extinct genus of arthropod containing the species P. venator known from the Silurian-aged Waukesha Biota of the Brandon Bridge Formation near Waukesha, Wisconsin. This animal has gone through a confusing taxonomic history, being called an arachnid, crustacean, and an artiopodan arthropod at various points. This animal is one of the more famous fossil finds from Wisconsin, due to the media coverage it received based on its original description in 2020 as a basal scorpion.
The Waukesha Biota is an important fossil site located in Waukesha County 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 Lagerstätten 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.
Venustulus is a genus of synziphosurine, a paraphyletic group of fossil chelicerate arthropods. Venustulus was regarded as part of the clade Prosomapoda. Fossils of the single and type species, V. waukeshaensis, have been discovered in deposits of the Silurian period in Wisconsin, in the United States. Venustulus is one of the few synziphosurine genera with fossil showing evidence of appendages, the other ones being Weinbergina, Anderella and Camanchia. Despite often being aligned close to horseshoe crabs, it has been found that Venustulus and its relatives form a group made up of various basal euchelicerate arthropods more distant to the xiphosurans.
Weis Earth Science Museum, located at 1478 Midway Rd, on the University of Wisconsin–Oshkosh, Fox Cities Campus in Menasha, Wisconsin, USA, was opened in 2002. It focuses on Wisconsin geology and its mining history. As such, it was designated as the Official Mineralogical Museum of Wisconsin by then-Governor Tommy Thompson in 2000, prior to its construction.
Acheronauta is a genus of extinct worm-shaped arthropod that lived in the early Silurian Waukesha biota fossil site in southeast Wisconsin. This arthropod was first discovered alongside the biota in 1985, but was not fully described until October 2022. This creature was recognized and described as a possible early mandibulate. This description is very important as much of the fauna of the biota remain undescribed, and its discovery has allowed for paleontologists to get a better grasp of the diversity of the arthropod fauna at the site. Multiple phylogenetic analyses were performed, and it was found that this arthropod forms a previously undiscovered clade with the Devonian stem-arthropod Captopodus, and the somewhat enigmatic group Thylacocephala.
Waukeshaaspis is an extinct genus of trilobite known from the lower Silurian aged Waukesha Biota. A single species is currently known, Waukeshaaspis eatonae, which is known from strata belonging to the Telychian aged Brandon Bridge Formation in Wisconsin. Originally discovered alongside the Waukesha Biota in 1985, this genus wouldn't be properly described until 2024. Currently, this genus is placed within the family Dalmanitidae, within the larger Phacopida, which lasted from the Lower Ordovician to the Upper Devonian.
Stranded scyphozoans (jellyfish) at Blackberry Hill.
Climactichnites wilsoni, these trails were made by a large, slug-like mollusk at Blackberry Hill. These examples are about 10 cm wide.
The trackway Protichnites from Blackberry Hill. These are believed to be some of the first footprints made on land. They were made by the euthycarcinoid arthropod Mosineia
The euthycarcinoid Mosineia macnaughtoni---the presumed maker of some of the Protichnites at Blackberry Hill, and hence one of the first animals to emerge from the sea and walk on land.
A conceptual drawing of M. macnaughtoni producing the Protichnites tracks.
A fossil showing the right side of Cyclopites , an aglaspidid arthropod from the Saint Lawrence Formation in Baraboo.
Aglaspis was another genus of aglaspidid native to Wisconsin.
A currently undescribed genus of scyphozoans (jellyfish) from the Mt. Simon Sandstone at Blackberry Hill
A carapace of the phyllocarid crustacean Arenosicaris inflata.
Fossils of sand stromatolites on rippled sandstone
The trackways Diplichnites could be produced by a variety of arthropods throughout the Phanerozoic fossil record, especially millipedes and trilobites in the Paleozoic. This example may have been produced by a euthycarcinoid.
Fossils of wave ripple marks with a microbial mat fossil on its surface.
A trace fossil resembling Rusophycus that was probably made by Arenosicaris inflata.
The Cambrian trilobite Saukiella pepinensis .
