Graptolites are a group of colonial animals, members of the subclass Graptolithina within the class Pterobranchia. These filter-feeding organisms are known chiefly from fossils found from the Middle Cambrian through the Lower Carboniferous (Mississippian). A possible early graptolite, Chaunograptus, is known from the Middle Cambrian. Recent analyses have favored the idea that the living pterobranch Rhabdopleura represents an extant graptolite which diverged from the rest of the group in the Cambrian. Fossil graptolites and Rhabdopleura share a colony structure of interconnected zooids housed in organic tubes (theca) which have a basic structure of stacked half-rings (fuselli). Most extinct graptolites belong to two major orders: the bush-like sessile Dendroidea and the planktonic, free-floating Graptoloidea. These orders most likely evolved from encrusting pterobranchs similar to Rhabdopleura. Due to their widespread abundance, planktonic lifestyle, and well-traced evolutionary trends, graptoloids in particular are useful index fossils for the Ordovician and Silurian periods.
Holoplankton are organisms that are planktic for their entire life cycle. Holoplankton can be contrasted with meroplankton, which are planktic organisms that spend part of their life cycle in the benthic zone. Examples of holoplankton include some diatoms, radiolarians, some dinoflagellates, foraminifera, amphipods, krill, copepods, and salps, as well as some gastropod mollusk species. Holoplankton dwell in the pelagic zone as opposed to the benthic zone. Holoplankton include both phytoplankton and zooplankton and vary in size. The most common plankton are protists.
Pterobranchia is a class of small worm-shaped animals. They belong to the Hemichordata, and live in secreted tubes on the ocean floor. Pterobranchia feed by filtering plankton out of the water with the help of cilia attached to tentacles. There are about 25 known living pterobranch species in three genera, which are Rhabdopleura, Cephalodiscus, and Atubaria. On the other hand, there are several hundred extinct genera, some of which date from the Cambrian Period.
Laurie Island is the second largest of the South Orkney Islands. The island is claimed by both Argentina as part of Argentine Antarctica, and the United Kingdom as part of the British Antarctic Territory. However, under the Antarctic Treaty System all sovereignty claims are frozen, as the island lies south of the parallel 60°. Buchanan Point at the north-eastern end of the island, with Cape Whitson on its south coast, are Important Bird Areas.
In the geologic timescale, the Aeronian is an age of the Llandovery Epoch of the Silurian Period of the Paleozoic Era of the Phanerozoic Eon that began 440.8 ± 1.2 Ma and ended 438.5 ± 1.1 Ma. The Aeronian Age succeeds the Rhuddanian Age and precedes the Telychian Age, all in the same epoch.
The Darriwilian is the upper stage of the Middle Ordovician. It is preceded by the Dapingian and succeeded by the Upper Ordovician Sandbian Stage. The lower boundary of the Darriwilian is defined as the first appearance of the graptolite species Undulograptus austrodentatus around 467.3 million years ago. It lasted for about 8.9 million years until the beginning of the Sandbian around 458.4 million years ago. This stage of the Ordovician was marked by the beginning of the Andean-Saharan glaciation.
Gertrude Lilian Elles MBE was a British geologist, known for her work on graptolites.
In the geologic timescale, the Gorstian is an age of the Ludlow Epoch of the Silurian Period of the Paleozoic Era of the Phanerozoic Eon that is comprehended between 427.4 ± 0.5 Ma and 425.6 ± 0.9 Ma, approximately. The Gorstian Age succeeds the Homerian Age and precedes the Ludfordian Age. The age is named after Gorsty village southwest of Ludlow. The base of the age is marked by Graptolites tumescens and Graptolites incipiens. The type section is located in a quarry in the Elton Formation at Pitch Coppice, Shropshire, United Kingdom.
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.
Dame Ethel Mary Reader Shakespear was an English geologist, Justice of the Peace, public servant, and philanthropist. She is most famously known for her work on the Lower Ludlow Formation and won several awards for her influential papers.
Monograptus is a genus of graptolites in the order Graptoloidea. This particular genus is the last stage of the graptoloid evolution before its extinction in the early Devonian. A characteristic of the genus includes one uniserial stipes with very elaborate thecae. This particular genus contains large number of graptolite species and may not be monophyletic.
Green Point is located 12 km north of the town of Rocky Harbour in Gros Morne National Park, on the west coast of Newfoundland. It is the home to a small summer fishing community and a drive-in campground. In 2000, Green Point was designated the Global Stratotype Section and Point (GSSP) representing the division between the Cambrian and the Ordovician systems.
Clonograptus is a genus of graptolites. Groups of these animals were connected by stalklike structures to a central region. Species of Clonograptus are zone fossils, and can be used to find the precise age of Ordovician rocks.
Ferrier Peninsula is a narrow peninsula, 2.4 km (1.5 mi) long, forming the eastern end of Laurie Island in the South Orkney Islands of Antarctica. It was roughly charted in 1823 by a British sealing expedition under James Weddell. It was surveyed in 1903 by the Scottish National Antarctic Expedition under William Speirs Bruce, who named it for his secretary J.G. Ferrier, who was also manager in Scotland of the expedition.
Graptolite Island is an island 0.8 km (0.50 mi) long in the north-east part of Fitchie Bay, lying off the south-east portion of Laurie Island in the South Orkney Islands of Antarctica. James Weddell's chart published in 1825 shows two islands in essentially this position. Existence of a single island was determined in 1903 by the Scottish National Antarctic Expedition under William Speirs Bruce, who so named it because what were thought to be graptolite fossils were found there. Later analysis showed that the fossils on Graptolite Island were merely the remains of ancient plants.
Rhabdopleurida is one of three orders in the class Pterobranchia, which are small, worm-shaped animals, are the only surviving graptolites. Members belong to the hemichordates. Species in this order are sessile, colonial, connected with a stolon, living in clear water and secrete tubes called tubarium. They have a single gonad, the gill slits are absent and the collar has two tentaculated arms. Rhabdopleura is the best studied pterobranch in developmental biology. Rhabdopleura is the only extant graptolite.
Callograptus is a genus of graptolites.
Anisograptidae is an extinct family of graptolites. As the first planktic graptolites, they play a crucial role for understanding the transition of graptolites from ocean floor suspension feeders to ocean surface plankton during the early Ordovician.
Dendrograptidae is an extinct family of graptolites.
The Lundgreni Event, also known as the Mid-Homerian Biotic Crisis, was an extinction event during the middle Homerian age of the Silurian period. Evidence for the event has been observed in Silurian marine deposits in the Iberian Peninsula, Bohemia, and Poland.
