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The Cambrian Period was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 55.6 million years from the end of the preceding Ediacaran Period 541 million years ago (mya) to the beginning of the Ordovician Period 485.4 mya. Its subdivisions, and its base, are somewhat in flux. The period was established as "Cambrian series" by Adam Sedgwick, who named it after Cambria, the Latin name for 'Cymru' (Wales), where Britain's Cambrian rocks are best exposed. The Cambrian is unique in its unusually high proportion of lagerstätte sedimentary deposits, sites of exceptional preservation where "soft" parts of organisms are preserved as well as their more resistant shells. As a result, our understanding of the Cambrian biology surpasses that of some later periods.
The geologic time scale (GTS) is a system of chronological dating that classifies geological strata (stratigraphy) in time. It is used by geologists, paleontologists, and other Earth scientists to describe the timing and relationships of events in geologic history. The time scale was developed through the study of physical rock layers and relationships as well as the times when different organisms appeared, evolved and became extinct through the study of fossilized remains and imprints. The table of geologic time spans, presented here, agrees with the nomenclature, dates and standard color codes set forth by the International Commission on Stratigraphy (ICS).
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.
Trilobites are a group of extinct marine artiopodan arthropods that form the class Trilobita. Trilobites form one of the earliest-known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the Atdabanian stage of the Early Cambrian period, and they flourished throughout the lower Paleozoic before slipping into a long decline, when, during the Devonian, all trilobite orders except the Proetida died out. The last extant trilobites finally disappeared in the mass extinction at the end of the Permian about 252 million years ago. Trilobites were among the most successful of all early animals, existing in oceans for almost 300 million years.
Gigantosaurus is a sauropod dinosaur genus from the Late Jurassic Kimmeridge Clay Formation of England. The type species, Gigantosaurus megalonyx, was named and described by Harry Govier Seeley in 1869. Its syntype series consists of several separately discovered sauropod bones found in Cambridgeshire, including two caudal (tail) vertebrae, the distal end of a tibia, a cast of the right radius, a cast of phalanx and an osteoderm. It was synonymised to Ornithopsis humerocristatus by Richard Lydekker in 1888 and to Pelorosaurus by Friedrich von Huene in 1909. Today it is considered a nomen dubium.
In the geologic timescale the Bathonian is an age and stage of the Middle Jurassic. It lasted from approximately 168.3 Ma to around 166.1 Ma. The Bathonian age succeeds the Bajocian age and precedes the Callovian age.
The Late Triassic is the third and final epoch of the Triassic Period in the geologic timescale. The Triassic-Jurassic extinction event began during this epoch and is one of the five major mass extinction events of the Earth. The corresponding series is known as the Upper Triassic. In Europe the epoch was called the Keuper, after a German lithostratigraphic group that has a roughly corresponding age. The Late Triassic spans the time between 237 Ma and 201.3 Ma. It is preceded by the Middle Triassic epoch and is followed by the Early Jurassic epoch. The Late Triassic is divided into the Carnian, Norian and Rhaetian ages.
Dakosaurus is an extinct genus within the family Metriorhynchidae that lived during the Late Jurassic and Early Cretaceous. It was large, with teeth that were serrated and compressed lateromedially. The genus was established by Friedrich August von Quenstedt in 1856 for an isolated tooth named Geosaurus maximus by Plieninger. Dakosaurus was a carnivore that spent much, if not all, its life out at sea. The extent of its adaptation to a marine lifestyle means that it is most likely that it mated at sea, but since no eggs or nests have been discovered that have been referred to Dakosaurus, whether it gave birth to live young at sea like dolphins and ichthyosaurs or came ashore like turtles is not known. The name Dakosaurus means "biter lizard", and is derived from the Greek dakos ("biter") and σαῦρος -sauros ("lizard").
Streptospondylus is a genus of tetanuran theropod dinosaur known from the Late Jurassic period of France, 161 million years ago. It was a medium-sized predator with an estimated length of 6 meters and a weight of 500 kg (1,100lbs).
Megarachne is a genus of eurypterid, an extinct group of aquatic arthropods. Fossils of Megarachne have been discovered in deposits of Late Carboniferous age, from the Gzhelian stage, in San Luis, Argentina. The fossils of the single and type species M. servinei have been recovered from deposits that had once been a freshwater environment. The generic name, composed of the Ancient Greek μέγας (megas) meaning "great" and Ancient Greek ἀράχνη (arachne) meaning "spider", translates to "great spider", because the fossil was misidentified as a large prehistoric spider.
Bramerton Pits is a 0.7-hectare (1.7-acre) geological Site of Special Scientific Interest north of the village of Bramerton in Norfolk on the southern banks of the River Yare. It is a Geological Conservation Review site.
Adelophthalmus is a genus of eurypterid, an extinct group of aquatic arthropods. Fossils of Adelophthalmus have been discovered in deposits ranging in age from the Early Devonian to the Early Permian, which makes it the longest lived of all known eurypterid genera, with a total temporal range of over 120 million years. Adelopthtalmus was the final genus of the Eurypterina suborder of eurypterids and consisted the only known genus of swimming eurypterids from the Middle Devonian until its extinction during the Permian, after which the few surviving eurypterids were all walking forms of the suborder Stylonurina.
Callawayasaurus is a genus of plesiosaur from the family Elasmosauridae. When the first Callawayasaurus fossil was first discovered by Samuel Paul Welles in 1962, it was described as Alzadasaurus colombiensis before being moved into its current genus by Kenneth Carpenter in 1999.
Eogavialis is an extinct genus of eusuchian crocodylomorph, usually regarded as a gavialoid crocodylian. It superficially resembles Tomistoma schlegelii, the extant false gharial, and consequently material from the genus was originally referred to Tomistoma. Indeed, it was not until 1982 that the name Eogavialis was constructed after it was realised that the specimens were from a more basal form.
The Red Crag Formation is a geological formation in England. It outcrops in south-eastern Suffolk and north-eastern Essex. The name derives from its iron-stained reddish colour and crag which is an East Anglian word for shells. It is part of the Crag Group, a series of notably marine strata which belong to a period when Britain was connected to continental Europe by the Weald–Artois Anticline, and the area in which the Crag Group was deposited was a tidally dominated marine bay. This bay would have been subjected to enlargement and contraction brought about by transgressions and regressions driven by the 40,000-year Milankovitch cycles.
Crustaceans form a large, diverse arthropod taxon which includes such animals as crabs, lobsters, crayfish, shrimps, prawns, krill, woodlice, and barnacles. The crustacean group can be treated as a subphylum under the clade Mandibulata; because of recent molecular studies it is now well accepted that the crustacean group is paraphyletic, and comprises all animals in the clade Pancrustacea other than hexapods. Some crustaceans are more closely related to insects and the other hexapods than they are to certain other crustaceans.
The Thanet Formation is a geological formation found in the London Basin of southeastern England. It is of early to mid-Thanetian age and gave its name to that stratigraphic interval. It was previously known as the Thanet Beds, the Thanet Sands and the Thanet Sand Formation. It was named after the Isle of Thanet. The type sections are Herne Bay in Kent for the upper part of the formation and Pegwell Bay for the lower part. It lies unconformably on the Late Cretaceous Chalk Group. It unconformably underlies the Lambeth Group, generally the Upnor Formation but in Essex it is the Reading Formation.
Dearcmhara is a genus of marine reptile from the early to mid-Jurassic period around 170 million years ago, known from fossil remains found on the island of Skye in Scotland. The type species is Dearcmhara shawcrossi. Fragmentary fossil remains of the animal were discovered by an amateur fossil hunter in 1959 and were subsequently donated to a museum, but it was not until 2014 that a scientific research project determined that the fossils were of a previously unknown species.
Palaeoscolex is the type genus of the Palaeoscolecid worms, and served as a wastebasket taxon. until its taxonomy was revised and many of its taxa assigned to Wronascolex.
Leyvachelys is an extinct genus of turtles in the family Sandownidae from the Early Cretaceous of the present-day Altiplano Cundiboyacense, Eastern Ranges, Colombian Andes. The genus is known only from its type species, Leyvachelys cipadi, described in 2015 by Colombian paleontologist Edwin Cadena. Fossils of Leyvachelys have been found in the fossiliferous Paja Formation, close to Villa de Leyva, Boyacá, after which the genus is named. The holotype specimen is the oldest and most complete sandownid turtle found to date.
References
- 1 2 Sepkoski, Jack (2002). "A compendium of fossil marine animal genera (Trilobita entry)". Bulletins of American Paleontology. 364: 560. Archived from the original on 2006-09-05. Retrieved 2008-01-12.
- ↑ "GB3D Type Fossils | High resolution photographs and digital models of British type fossils". www.3d-fossils.ac.uk. Retrieved 2020-07-13.
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