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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.
Traditionally, the Myodocopa and Podocopa have been classified as subclasses within the class Ostracoda, although there is some question about how closely related the two groups actually are. The Myodocopa are defined by possession of a poorly calcified carapace, and 8–9 articles in the exopod of the second antenna. The ventral margin of the carapace is not concave, and the valves do not overlap to a great extent.
Cylindroleberididae is a family of ostracods that shows remarkable morphological diversity. The defining feature is the possession of gills: 7–8 leaf-like pairs at the posterior of the body. Other features common to all species in the family include a "baleen-comb" on both the maxilla and the fifth limb, a sword-shaped coxal endite on the mandible, and the triaenid bristles on the basal endites of the mandible.
Birkenia is a genus of extinct anaspid fish from Middle Silurian strata of Northern Europe, and Middle Silurian to possibly Earliest Devonian strata of Arctic Canada. Birkeniid anaspids are covered by a series of small plates on the head and rod-shaped scales in a cheveron-like pattern on the trunk.
Phlebolepis is an extinct thelodont agnathan genus belonging to the family Phlebolepididae. Whole fossils are found in Late Silurian aged strata from Saaremaa, Estonia. Phlebolepis elegans was average-sized for a thelodont, 7 cm long.
Acutiramus is a genus of giant predatory eurypterid, an extinct group of aquatic arthropods. Fossils of Acutiramus have been discovered in deposits of Late Silurian to Early Devonian age. Seven species have been described, five from North America and two from the Czech Republic. The generic name derives from Latin acuto and Latin ramus ("branch"), referring to the acute angle of the final tooth of the claws relative to the rest of the claw.
Suchomasty is a municipality and village in Beroun District in the Central Bohemian Region of the Czech Republic. It has about 500 inhabitants.
The Late Silurian to Early Devonian Keyser Formation is a mapped limestone bedrock unit in Pennsylvania, Maryland, Virginia, and West Virginia.
Plumulites is an extinct genus of machaeridians, extinct annelid group.
Aulacopleura is a genus of proetid trilobite that lived from the Middle Ordovician to the Middle Devonian. Some authors may classify this group as subgenus Otarion (Aulacopleura). The cephalon is semicircular or semielliptical, with border and preglabellar field. The glabella is short, with or without defined eye ridges connecting it with eyes of variable size. Spines at the rear outer corners of the cephalon are present, typically reaching back to the 2nd to 4th thorax segment. The 'palate' is not connected to the dorsal shield of the cephalon. The cephalon is pitted, or has small tubercles. The thorax has up to 22 segments. The pleural ends are usually rounded. The pygidium is small (micropygous), with an even margin. A. koninckii had a modern type of compound eye.
Camarotoechia is an extinct genus of brachiopods found in Paleozoic strata.
Bohemiatupus is an extinct genus of griffenfly in the family Meganeuridae and containing a single species Bohemiatupus elegans. The species is known only from the Late Carboniferous, Bolsovian stage, Kladno Formation near the village of Radnice in the Radnice Basin, Czech Republic.
The Man on the Hill (MOTH) locality of northwestern Canada has fossils that are very well preserved and have had a profound impact on the understanding of vertebrate evolution. The geology of the MOTH locality consists of fine, alternating laminae of light grey argillaceous limestone, or calcareous shale, and dark grey silt to sand-rich calcareous shale, as observed in thin section, and the characterization of the lithology for the vertebrate-bearing strata as an interlaminated argillaceous limestone and calcareous shale. The abundance of cryptic trace fossils and the presence of pyrite suggest that the intra-shelf topographic sag at MOTH had restricted circulation and was generally hypoxic.
Callograptus is a genus of graptolites.
Oulodus is a genus of conodonts in the family Prioniodinidae.
Cicerocrinus is an extinct genus of crinoids in the family Pisocrinidae. It is known from the Silurian of the United Kingdom. The type locality for C. elegans is Old Bridge near Ludlow.
Catenipora is an extinct genus of tabulate corals in the family Halysitidae, known from the Ordovician to the Silurian.
Phragmolites is an extinct genus of molluscs in the family Bucaniidae, paleozoic molluscs of uncertain position possibly being either Gastropods or Monoplacophorans in the superfamily Bellerophontoidea.
Amphissites is an extinct genus of ostracod belonging to the suborder Beyrichicopina and family Amphissitinae. Species belonging to the genus lived from the Devonian to the Permian in Europe, North America, Australia, and east Asia. The genus were likely deposit-feeders, and may have survived briefly into the Triassic.
Dudleyaspis is an extinct genus of Lower to Middle Devonian odontopleurid trilobites that lived in a shallow sea that lay between Euramerica and Gondwana. It was named in 1949 by Prantl & Pribyl.
References
- ↑ Middle Ordovician ostracodes of central and southern Sweden, V Jaanusson, 1957
- ↑ Ostracodes from the Silurian of central Bohemia. A Přibyl, Sbornik Geologickysh Ved Paleontologie, 1988
- ↑ Neue Ostrakoden ans märkischen Silurgeschieben. A Krause, Zeitschrift der Deutschen Geologischen Gesellschaft, 1892
