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An extinction event is a widespread and rapid decrease in the biodiversity on Earth. Such an event is identified by a sharp change in the diversity and abundance of multicellular organisms. It occurs when the rate of extinction increases with respect to the background extinction rate and the rate of speciation. Estimates of the number of major mass extinctions in the last 540 million years range from as few as five to more than twenty. These differences stem from disagreement as to what constitutes a "major" extinction event, and the data chosen to measure past diversity.
The gastropods, commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda.
Mosasaurs comprise a group of extinct, large marine reptiles from the Late Cretaceous. Their first fossil remains were discovered in a limestone quarry at Maastricht on the Meuse in 1764. They belong to the order Squamata, which includes lizards and snakes.
Goniatids, informally goniatites, are ammonoid cephalopods that form the order Goniatitida, derived from the more primitive Agoniatitida during the Middle Devonian some 390 million years ago. Goniatites (goniatitids) survived the Late Devonian extinction to flourish during the Carboniferous and Permian only to become extinct at the end of the Permian some 139 million years later.
Clam shrimp are a group of bivalved branchiopod crustaceans that resemble the unrelated bivalved molluscs. They are extant and also known from the fossil record, from at least the Devonian period and perhaps before. They were originally classified in the former order Conchostraca, which later proved to be paraphyletic and was subsumed into the superorder Diplostraca. Clam shrimp now make up three of the seven orders in Diplostraca, Cyclestherida, Laevicaudata, and Spinicaudata, in addition to the fossil family Leaiidae.
A microfossil is a fossil that is generally between 0.001 mm and 1 mm in size, the visual study of which requires the use of light or electron microscopy. A fossil which can be studied with the naked eye or low-powered magnification, such as a hand lens, is referred to as a macrofossil.
An interglacial period is a geological interval of warmer global average temperature lasting thousands of years that separates consecutive glacial periods within an ice age. The current Holocene interglacial began at the end of the Pleistocene, about 11,700 years ago.
The Emsian is one of three faunal stages in the Early Devonian Epoch. It lasted from 407.6 ± 2.6 million years ago to 393.3 ± 1.2 million years ago. It was preceded by the Pragian Stage and followed by the Eifelian Stage. It is named after the Ems river in Germany. The GSSP is located in the Zinzil'ban Gorge in the Kitab State Geological Reserve of Uzbekistan, 35 centimetres (14 in) above the contact with the Madmon Formation.
Sirenia is the order of placental mammals which comprises modern "sea cows" and their extinct relatives. They are the only extant herbivorous marine mammals and the only group of herbivorous mammals to have become completely aquatic. Sirenians are thought to have a 50-million-year-old fossil record. They attained modest diversity during the Oligocene and Miocene, but have since declined as a result of climatic cooling, oceanographic changes, and human interference. Two genera and four species are extant: Trichechus, which includes the three species of manatee that live along the Atlantic coasts and in rivers and coastlines of the Americas and western Africa, and Dugong, which is found in the Indian and Pacific oceans.
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.
Monte San Giorgio is a mountain and UNESCO World Heritage Site on the border between Switzerland and Italy. It is part of the Lugano Prealps, overlooking Lake Lugano in the Swiss Canton of Ticino.
In geology, the Arenig is a time interval during the Ordovician period and also the suite of rocks which were deposited during this interval.
Vinctifer is an extinct genus of prehistoric bony fish erected by David Starr Jordan in 1919.
Chongichthys is an extinct genus of prehistoric bony fish that lived during the Oxfordian stage of the Late Jurassic epoch. Fossils of the genus have been found in the Quebrada El Profeta of Chile.
The Dresbachian is a Maentwrogian regional stage of North America, lasting from 501 to 497 million years ago. It is part of the Upper Cambrian and is defined by four trilobite zones. It overlaps with the ICS-stages Guzhangian, Paibian and the lowest Jiangshanian.
Tarpons are fish of the genus Megalops. They are the only members of the family Megalopidae. Of the two species, one is native to the Atlantic, and the other to the Indo-Pacific Oceans.
Crustaceans may pass through a number of larval and immature stages between hatching from their eggs and reaching their adult form. Each of the stages is separated by a moult, in which the hard exoskeleton is shed to allow the animal to grow. The larvae of crustaceans often bear little resemblance to the adult, and there are still cases where it is not known what larvae will grow into what adults. This is especially true of crustaceans which live as benthic adults, more-so than where the larvae are planktonic, and thereby easily caught.
Megacephalosaurus is an extinct genus of short-necked pliosaur that inhabited the Western Interior Seaway of North America about 94 to 93 million years ago during the Turonian stage of the Late Cretaceous, containing the single species M. eulerti. It is named after its large head, which is the largest of any plesiosaur in the continent and measures up to 1.75 meters (5.7 ft) in length. Megacephalosaurus was one of the largest marine reptiles of its time with an estimated length of 6–9 meters (20–30 ft). Its long snout and consistently sized teeth suggest that it preferred a diet on smaller-sized prey.
Crustaceans form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group can be treated as a subphylum under the clade Mandibulata. It is now well accepted that the hexapods emerged deep in the Crustacean group, with the completed group referred to as Pancrustacea. Some crustaceans are more closely related to insects and the other hexapods than they are to certain other crustaceans.
Caveasphaera is a multicellular organism found in 609-million-year-old rocks laid down during the Ediacaran period in the Guizhou Province of South China. The organism is not easily defined as an animal or non-animal. The organism is notable due to the study of related embryonic fossils which display different stages of its development: from early single-cell stages to later multicellular stages. Such fossil studies present the earliest evidence of an essential step in animal evolution – the ability to develop distinct tissue layers and organs. According to researchers, fossil studies of Caveasphaera have suggested that animal-like embryonic development arose much earlier than the oldest clearly defined animal fossils and may be consistent with studies suggesting that animal evolution may have begun about 750 million years ago. Nonetheless, Caveasphaera fossils may look similar to starfish and coral embryos. Still, researchers have concluded, "Parental investment in the embryonic development of Caveasphaera and co-occurring Tianzhushania and Spiralicellula, as well as delayed onset of later development, may reflect an adaptation to the heterogeneous nature of the early Ediacaran nearshore marine environments in which early animals evolved."
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.
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