Thomas Cavalier-Smith
Thomas Cavalier-Smith, FRS, FRSC, NERC Professorial Fellow, is a Professor of Evolutionary Biology in the Department of Zoology, at the University of Oxford. His research has led to discovery of a number of unicellular organisms and definition of taxonomic positions, such as introduction of the kingdom Chromista, other groups including Chromalveolata, Opisthokonta and Excavata, he is well known for his system of classification of all organisms. Cavalier-Smith was born on 21 October 1942 in London, his parents were Mary Maude Cavalier-Smith. He was educated at Norwich School and Caius College and King's College London, he was under the supervision of Sir John Randall for his PhD thesis between 1964 and 1967. From 1967 to 1969, he was a guest investigator at Rockefeller University, he became Lecturer of biophysics at King's College London in 1969. He was promoted to Reader in 1982. In 1989 he was appointed Professor of botany at the University of British Columbia. In 1999, he joined the University of Oxford, becoming Professor of evolutionary biology in 2000.
Cavalier-Smith was elected Fellow of the Linnean Society of London in 1980, the Institute of Biology in 1983, the Royal Society of Arts in 1987, the Canadian Institute for Advanced Research in 1988, the Royal Society of Canada in 1997, the Royal Society of London in 1998. He received the International Prize for Biology from the Emperor of Japan in 2004, the Linnean Medal for Zoology in 2007, he was appointed Fellow of the Canadian Institute for Advanced Research between 1998 and 2007, Advisor of the Integrated Microbial Biodiversity of CIFAR. He won the 2007 Frink Medal of the Zoological Society of London. Cavalier-Smith has written extensively on the classification of protists. One of his major contributions to biology was his proposal of a new kingdom of life: the Chromista, he introduced a new group for primitive eukaryotes called the Chromalveolata, as well as Opisthokonta and Excavata. Though well known, many of his claims have been controversial and have not gained widespread acceptance in the scientific community to date.
His taxonomic revisions lead to changes in the overall classification of all life forms. Cavalier-Smith's first major classification system was the division of all organisms into eight kingdoms. In 1981, he proposed that by revising Robert Whittaker's Five Kingdom system, there could be eight kingdoms: Bacteria, Ciliofungi, Biliphyta, Viridiplantae and Euglenozoa. In 1993, he revised his system in the light of the general acceptance of Archaebacteria as separate group from Bacteria. In addition, some protists lacking mitochondria were discovered; as mitochondria were known to be the result of the endosymbiosis of a proteobacterium, it was thought that these amitochondriate eukaryotes were primitively so, marking an important step in eukaryogenesis. As a result, these amitochondriate protists were separated from the protist kingdom, giving rise to the, at the same time and kingdom Archezoa; this was known as the Archezoa hypothesis. The eight kingdoms became: Eubacteria, Archezoa, Chromista, Plantae and Animalia.
However, kingdom Archezoa is now defunct. He now assigns former members of the kingdom Archezoa to the phylum Amoebozoa. By 1998, Cavalier-Smith had reduced the total number of kingdoms from eight to six: Animalia, Fungi, Plantae and Bacteria, he had presented this simplified scheme for the first time on his 1981 paper and endorsed it in 1983. Five of Cavalier-Smith's kingdoms are classified as eukaryotes as shown in the following scheme: Eubacteria Neomura Archaebacteria Eukaryotes Kingdom Protozoa Unikonts Kingdom Animalia Kingdom Fungi Bikonts Kingdom Plantae Kingdom ChromistaThe kingdom Animalia was divided into four subkingdoms: Radiata, Myxozoa and Bilateria, he created three new animal phyla: Acanthognatha and Lobopoda and recognised a total of 23 animal phyla. Cavalier-Smith's 2003 classification scheme: Unikonts protozoan phylum Amoebozoa opisthokonts uniciliate protozoan phylum Choanozoa kingdom Fungi kingdom Animalia Bikonts protozoan infrakingdom Rhizaria phylum Cercozoa phylum Retaria protozoan infrakingdom Excavata phylum Loukozoa phylum Metamonada phylum Euglenozoa phylum Percolozoa protozoan phylum Apusozoa the chromalveolate clade kingdom Chromista protozoan infrakingdom Alveolata phylum Ciliophora phylum Miozoa kingdom Plantae Cavalier-Smith and his collaborators revised the classification in 2015, published it in PLOS ONE.
In this scheme they reintroduced the division of prokaryotes into two kingdoms and Archaea. This is based on the consensus in the Taxonomic Outline of Bacteria and Archaea and the Catalogue of Life. In 2006, Cavalier-Smith proposed that the last universal common ancestor to all life was a non-flagellate negibacterium with two membranes. University of Oxford Faculty Web Page for T. Cavalier-Smith T. Cavalier-Smith on
Geochronology
Geochronology is the science of determining the age of rocks and sediments using signatures inherent in the rocks themselves. Absolute geochronology can be accomplished through radioactive isotopes, whereas relative geochronology is provided by tools such as palaeomagnetism and stable isotope ratios. By combining multiple geochronological indicators the precision of the recovered age can be improved. Geochronology is different in application from biostratigraphy, the science of assigning sedimentary rocks to a known geological period via describing and comparing fossil floral and faunal assemblages. Biostratigraphy does not directly provide an absolute age determination of a rock, but places it within an interval of time at which that fossil assemblage is known to have coexisted. Both disciplines work together hand in hand, however, to the point where they share the same system of naming rock layers and the time spans utilized to classify layers within a stratum; the science of geochronology is the prime tool used in the discipline of chronostratigraphy, which attempts to derive absolute age dates for all fossil assemblages and determine the geologic history of the Earth and extraterrestrial bodies.
By measuring the amount of radioactive decay of a radioactive isotope with a known half-life, geologists can establish the absolute age of the parent material. A number of radioactive isotopes are used for this purpose, depending on the rate of decay, are used for dating different geological periods. More decaying isotopes are useful for longer periods of time, but less accurate in absolute years. With the exception of the radiocarbon method, most of these techniques are based on measuring an increase in the abundance of a radiogenic isotope, the decay-product of the radioactive parent isotope. Two or more radiometric methods can be used in concert to achieve more robust results. Most radiometric methods are suitable for geological time only, but some such as the radiocarbon method and the 40Ar/39Ar dating method can be extended into the time of early human life and into recorded history; some of the used techniques are: Radiocarbon dating. This technique measures the decay of carbon-14 in organic material and can be best applied to samples younger than about 60,000 years.
Uranium–lead dating. This technique measures the ratio of two lead isotopes to the amount of uranium in a mineral or rock. Applied to the trace mineral zircon in igneous rocks, this method is one of the two most used for geologic dating. Monazite geochronology is another example of U–Pb dating, employed for dating metamorphism in particular. Uranium–lead dating is applied to samples older than about 1 million years. Uranium–thorium dating; this technique is used to date speleothems, corals and fossil bones. Its range is from a few years to about 700,000 years. Potassium–argon dating and argon–argon dating; these techniques date metamorphic and volcanic rocks. They are used to date volcanic ash layers within or overlying paleoanthropologic sites; the younger limit of the argon–argon method is a few thousand years. Electron spin resonance dating A series of related techniques for determining the age at which a geomorphic surface was created, or at which surficial materials were buried. Exposure dating uses the concentration of exotic nuclides produced by cosmic rays interacting with Earth materials as a proxy for the age at which a surface, such as an alluvial fan, was created.
Burial dating uses the differential radioactive decay of 2 cosmogenic elements as a proxy for the age at which a sediment was screened by burial from further cosmic rays exposure. Luminescence dating techniques observe'light' emitted from materials such as quartz, diamond and calcite. Many types of luminescence techniques are utilized in geology, including optically stimulated luminescence, cathodoluminescence, thermoluminescence. Thermoluminescence and optically stimulated luminescence are used in archaeology to date'fired' objects such as pottery or cooking stones and can be used to observe sand migration. Incremental dating techniques allow the construction of year-by-year annual chronologies, which can be fixed or floating. Dendrochronology Ice cores Lichenometry Varves A sequence of paleomagnetic poles, which are well defined in age, constitutes an apparent polar wander path; such a path is constructed for a large continental block. APWPs for different continents can be used as a reference for newly obtained poles for the rocks with unknown age.
For paleomagnetic dating, it is suggested to use the APWP in order to date a pole obtained from rocks or sediments of unknown age by linking the paleopole to the nearest point on the APWP. Two methods of paleomagnetic dating have been suggested Rotation method. First method is used for paleomagnetic dating of rocks inside of the same continental block; the second method is used for the folded areas. Magnetostratigraphy determines age from the pattern of magnetic polarity zones in a series of bedded sedimentary and/or volcanic rocks by comparison to the magnetic polarity timescale; the polarity timescale has been determined by dating of seafloor magnetic anomalies, radiometrically dating volcanic rocks within magnetostratigraphic sections, astronomically dating magnetostratigraphic sections. Global trends in isotope compositions Carbon 13 and strontium isotopes, can be used to corr
Microtubule
Microtubules are polymers of tubulin that form part of the cytoskeleton and provide structure and shape to the cytoplasm of eukaryotic cells, some bacteria and some archaea. A microtubule can grow as long as 50 micrometres and are dynamic; the outer diameter of a microtubule is about 24 nm. They are formed by the polymerization of a dimer of two globular proteins and beta tubulin into protofilaments that can associate laterally to form a hollow tube, the microtubule; the most common form of a microtubule consists of 13 protofilaments in the tubular arrangement. Microtubules are important in a number of cellular processes, they are involved in maintaining the structure of the cell and, together with microfilaments and intermediate filaments, they form the cytoskeleton. They make up the internal structure of cilia and flagella, they provide platforms for intracellular transport and are involved in a variety of cellular processes, including the movement of secretory vesicles and intracellular macromolecular assemblies.
They are involved in cell division and are the major constituents of mitotic spindles, which are used to pull eukaryotic chromosomes apart. Microtubules are nucleated and organized by microtubule organizing centers, such as the centrosome found in the center of many animal cells or the basal bodies found in cilia and flagella, or the spindle pole bodies found in most fungi. There are many proteins that bind to microtubules, including the motor proteins kinesin and dynein, severing proteins like katanin, other proteins important for regulating microtubule dynamics. An actin-like protein has been found in a gram-positive bacterium Bacillus thuringiensis, which forms a microtubule-like structure and is involved in plasmid segregation. Tubulin and microtubule-mediated processes, like cell locomotion, were seen by early microscopists, like Leeuwenhoek. However, the fibrous nature of flagella and other structures were discovered two centuries with improved light microscopes, confirmed in the 20th century with the electron microscope and biochemical studies.
Microtubule in vitro assays for motor proteins such as dynein and kinesin are researched by fluorescently tagging a microtubule and fixing either the microtubule or motor proteins to a microscope slide visualizing the slide with video-enhanced microscopy to record the travel of the microtubule motor proteins. This allows the movement of the motor proteins along the microtubule or the microtubule moving across the motor proteins; some microtubule processes can be determined by kymograph. In eukaryotes, microtubules are long, hollow cylinders made up of polymerised α- and β-tubulin dimers; the inner space of the hollow microtubule cylinders is referred to as the lumen. The α and β-tubulin subunits are 50% identical at the amino acid level, each have a molecular weight of 50 kDa; these α/β-tubulin dimers polymerize end-to-end into linear protofilaments that associate laterally to form a single microtubule, which can be extended by the addition of more α/β-tubulin dimers. Microtubules are formed by the parallel association of thirteen protofilaments, although microtubules composed of fewer or more protofilaments have been observed in vitro.
Microtubules have a distinct polarity, critical for their biological function. Tubulin polymerizes end to end, with the β-subunits of one tubulin dimer contacting the α-subunits of the next dimer. Therefore, in a protofilament, one end will have the α-subunits exposed while the other end will have the β-subunits exposed; these ends are designated ends, respectively. The protofilaments bundle parallel to one another with the same polarity, so, in a microtubule, there is one end, the end, with only β-subunits exposed, while the other end, the end, has only α-subunits exposed. While microtubule elongation can occur at both the and ends, it is more rapid at the end; the lateral association of the protofilaments generates a pseudo-helical structure, with one turn of the helix containing 13 tubulin dimers, each from a different protofilament. In the most common "13-3" architecture, the 13th tubulin dimer interacts with the next tubulin dimer with a vertical offset of 3 tubulin monomers due to the helicity of the turn.
There are other alternative architectures, such as 11-3, 12-3, 14-3, 15-4, or 16-4, that have been detected at a much lower occurrence. Microtubules can morph into other forms such as helical filaments, which are observed in protist organisms like foraminifera. There are two distinct types of interactions that can occur between the subunits of lateral protofilaments within the microtubule called the A-type and B-type lattices. In the A-type lattice, the lateral associations of protofilaments occur between adjacent α and β-tubulin subunits. In the B-type lattice, the α and β-tubulin subunits from one protofilament interact with the α and β-tubulin subunits from an adjacent protofilament, respectively. Experimental studies have shown that the B-type lattice is the primary arrangement within microtubules. However, in most microtubules there is a seam in which tubulin subunits interact α-β; some species of Prosthecobacter contain microtubules. The structure of these bacterial microtubules is similar to that of eukaryotic microtubules, consisting of a hollow tube of protofilaments assembled from heterodimers of bacterial tubulin A and bacterial tubulin B.
Both BtubA and BtubB share features of both α- and β-tubulin. Unlike eukar
Acantharea
The Acantharea are a group of radiolarian protozoa, distinguished by their strontium sulfate skeletons. Acantharian skeletons are composed of strontium sulfate crystals secreted by vacuoles surrounding each spicule or spine. Acantharians are the only marine organisms known to biomineralize strontium sulfate as the main component of their skeletons, making them quite unique. Unlike other radiolarians, whose skeletons are made of silica, acantharian skeletons do not fossilize because strontium sulfate is scarce in seawater and the crystals dissolve after the acantharians die; the skeletons are made up of twenty radial spicules. Diametric spicules cross the center of the cell, whereas radial spicules terminate at the center of the cell where they either form a tight or flexible junction depending on species; the cell is divided into two regions: the ectoplasm. The endoplasm, at the core of the cell, contains the main organelles, including many nuclei, is delineated from the ectoplasm by a capsular wall made of a microfibril mesh.
In symbiotic species, the algal symbionts are maintained in the endoplasm. The ectoplasm consists of cytoplasmic extensions used for prey capture and contains food vacuoles for prey digestion; the ectoplasm is surrounded by a periplasmic cortex made up of microfibrils, but arranged into twenty plates, each with a hole through which one spicule projects. The cortex is linked to the spines by contractile myonemes, which assist in buoyancy control by allowing the ectoplasm to expand and contract and decreasing the total volume of the cell; the arrangement of the spines is precise, is described by what is called the Müllerian law, which can be described in terms of lines of latitude and longitude – the spines lie on the intersections between five of the former, symmetric about an equator, eight of the latter, spaced uniformly. Each line of longitude carries either two tropical spines or one equatorial and two polar spines, in alternation; the way that the spines are joined together at the center of the cell varies and is one of the primary characteristics by which acantharians are classified.
Acantharians with diametric spicules or loosely attached radial spicules are able to rearrange or shed spicules and form cysts. Holacanthida – 10 diametric spicules crossed, no central junction, capable of encystment Chaunacanthida – 20 radial spicules, loosely attached, capable of encystment Symphiacanthida – 20 radial spicules, tight central junction Arthracanthida – 20 radial spines, tight central junctionThe morphological classification system agrees with phylogenetic trees based on the alignment of ribosomal RNA genes, although the groups are polyphyletic. Holacanthida seems to have evolved first and includes molecular clades A, B, D. Chaunacanthida evolved second and includes only one molecular clade, clade C. Arthracanthida and Symphacanthida, which have the most complex skeletons, evolved most and constitute molecular clades E and F. Many acantharians, including some in clade B and all in clades E & F, host single-celled algae within their inner cytoplasm. By participating in this photosymbiosis, acantharians are mixotrophs: they acquire energy through both heterotrophy and autotrophy.
The relationship may make it possible for acantharians to be abundant in low-nutrient regions of the oceans and may provide extra energy necessary to maintain their elaborate strontium sulfate skeletons. It is hypothesized that the acantharians provide the algae with nutrients that they acquire by capturing and digesting prey in return for sugar that the algae produces during photosynthesis, it is not known, whether the algal symbionts benefit from the relationship or if they are being exploited and digested by the acantharians. Symbiotic Holacanthida acantharians host diverse symbiont assemblages, including several genera of dinoflagellates and a haptophyte. Clade E & F acantharians have a more specific symbiosis and host symbionts from the haptophyte genus Phaeocystis, although they sometimes host Chrysochromulina symbionts. Clade F acantharians host multiple species and strains of Phaeocystis and their internal symbiont community does not match the relative availability of potential symbionts in the surrounding environment.
The mismatch between internal and external symbiont communities suggests that acantharians can be selective in choosing symbionts and do not continuously digest and recruit new symbionts, maintain symbionts for extended periods of time instead. Adults are multinucleated. Reproduction is thought to take place by formation of swarmer cells. Not all life cycle stages have been observed, study of these organisms has been hampered by an inability to maintain these organisms in culture through successive generations
Test (biology)
In biology, a test is the hard shell of some spherical marine animals, notably sea urchins and microorganisms such as testate foraminiferans and testate amoebae. The anatomical term "test" derives from the Latin testa, it is distinct from the term "test" as in "examination", which derives from testis, related to the idea of testimony. The test is a skeletal structure, made of hard material such as calcium carbonate, chitin or composite materials; as such, it allows the attachment of soft flesh. The test of sea urchins is made of calcium carbonate, strengthened by a framework of calcite monocrystals, in a characteristic "stereomic" structure; these two ingredients provide sea urchins with a great solidity and a moderate weight, as well as the capacity to regenerate the mesh from the cuticle. According to a 2012 study, the skeletal structures of sea urchins consist of 92% of "bricks" of calcite monocrystals and 8% of a "mortar" of amorphous lime; this lime is constituted itself of 99.9% of calcium carbonate, with 0.1% structural proteins, which make sea urchins animals with an mineralized skeleton.
The test of foraminiferan consists of mineralized organic matter, but sometimes exogenous agglomerated particles. It can be of many types, like agglutinated, porcelain-like or hyalin. Foraminiferans develops by building new rooms in their test; these are arranged according to a geometry particular to each species: they can be rectilinear, rolled up or cyclic, every time uniserial or multiserial. These organizational types can be mixed, or more complex. Miliolids have a particular arrangement; the surface of the test can be textured. In ascidians the sheath is sometimes called test as well, is composed of a particular type of cellulose termed "tunicine". From 1845 until 1958, ascidians were believed to be the only animals. On a scientific point of view, the term "test" should be restricted to the hard shell protecting sea urchins and foraminiferans. For sessile echinoderms, the correct word is "theca". For diatomea, the term in use is "frustule", for radiolarians it should be "capsule"; the more common word "shell" is used for mollusks and turtles.
Frustule Lorica
Cretaceous
The Cretaceous is a geologic period and system that spans 79 million years from the end of the Jurassic Period 145 million years ago to the beginning of the Paleogene Period 66 mya. It is the last period of the Mesozoic Era, the longest period of the Phanerozoic Eon; the Cretaceous Period is abbreviated K, for its German translation Kreide. The Cretaceous was a period with a warm climate, resulting in high eustatic sea levels that created numerous shallow inland seas; these oceans and seas were populated with now-extinct marine reptiles and rudists, while dinosaurs continued to dominate on land. During this time, new groups of mammals and birds, as well as flowering plants, appeared; the Cretaceous ended with the Cretaceous–Paleogene extinction event, a large mass extinction in which many groups, including non-avian dinosaurs and large marine reptiles died out. The end of the Cretaceous is defined by the abrupt Cretaceous–Paleogene boundary, a geologic signature associated with the mass extinction which lies between the Mesozoic and Cenozoic eras.
The Cretaceous as a separate period was first defined by Belgian geologist Jean d'Omalius d'Halloy in 1822, using strata in the Paris Basin and named for the extensive beds of chalk, found in the upper Cretaceous of Western Europe. The name Cretaceous was derived from Latin creta; the Cretaceous is divided into Early and Late Cretaceous epochs, or Lower and Upper Cretaceous series. In older literature the Cretaceous is sometimes divided into three series: Neocomian and Senonian. A subdivision in eleven stages, all originating from European stratigraphy, is now used worldwide. In many parts of the world, alternative local subdivisions are still in use; as with other older geologic periods, the rock beds of the Cretaceous are well identified but the exact age of the system's base is uncertain by a few million years. No great extinction or burst of diversity separates the Cretaceous from the Jurassic. However, the top of the system is defined, being placed at an iridium-rich layer found worldwide, believed to be associated with the Chicxulub impact crater, with its boundaries circumscribing parts of the Yucatán Peninsula and into the Gulf of Mexico.
This layer has been dated at 66.043 Ma. A 140 Ma age for the Jurassic-Cretaceous boundary instead of the accepted 145 Ma was proposed in 2014 based on a stratigraphic study of Vaca Muerta Formation in Neuquén Basin, Argentina. Víctor Ramos, one of the authors of the study proposing the 140 Ma boundary age sees the study as a "first step" toward formally changing the age in the International Union of Geological Sciences. From youngest to oldest, the subdivisions of the Cretaceous period are: Late Cretaceous Maastrichtian – Campanian – Santonian – Coniacian – Turonian – Cenomanian – Early Cretaceous Albian – Aptian – Barremian – Hauterivian – Valanginian – Berriasian – The high sea level and warm climate of the Cretaceous meant large areas of the continents were covered by warm, shallow seas, providing habitat for many marine organisms; the Cretaceous was named for the extensive chalk deposits of this age in Europe, but in many parts of the world, the deposits from the Cretaceous are of marine limestone, a rock type, formed under warm, shallow marine circumstances.
Due to the high sea level, there was extensive space for such sedimentation. Because of the young age and great thickness of the system, Cretaceous rocks are evident in many areas worldwide. Chalk is a rock type characteristic for the Cretaceous, it consists of coccoliths, microscopically small calcite skeletons of coccolithophores, a type of algae that prospered in the Cretaceous seas. In northwestern Europe, chalk deposits from the Upper Cretaceous are characteristic for the Chalk Group, which forms the white cliffs of Dover on the south coast of England and similar cliffs on the French Normandian coast; the group is found in England, northern France, the low countries, northern Germany, Denmark and in the subsurface of the southern part of the North Sea. Chalk is not consolidated and the Chalk Group still consists of loose sediments in many places; the group has other limestones and arenites. Among the fossils it contains are sea urchins, belemnites and sea reptiles such as Mosasaurus. In southern Europe, the Cretaceous is a marine system consisting of competent limestone beds or incompetent marls.
Because the Alpine mountain chains did not yet exist in the Cretaceous, these deposits formed on the southern edge of the European continental shelf, at the margin of the Tethys Ocean. Stagnation of deep sea currents in middle Cretaceous times caused anoxic conditions in the sea water leaving the deposited organic matter undecomposed. Half the worlds petroleum reserves were laid down at this time in the anoxic conditions of what would become the Persian Gulf and the Gulf of Mexico. In many places around the world, dark anoxic shales were formed during this interval; these shales are an important source rock for oil and gas, for example in the subsurface of the North Sea. During th
Jurassic
The Jurassic period was a geologic period and system that spanned 56 million years from the end of the Triassic Period 201.3 million years ago to the beginning of the Cretaceous Period 145 Mya. The Jurassic constitutes the middle period of the Mesozoic Era known as the Age of Reptiles; the start of the period was marked by the major Triassic–Jurassic extinction event. Two other extinction events occurred during the period: the Pliensbachian-Toarcian extinction in the Early Jurassic, the Tithonian event at the end; the Jurassic period is divided into three epochs: Early and Late. In stratigraphy, the Jurassic is divided into the Lower Jurassic, Middle Jurassic, Upper Jurassic series of rock formations; the Jurassic is named after the Jura Mountains within the European Alps, where limestone strata from the period were first identified. By the beginning of the Jurassic, the supercontinent Pangaea had begun rifting into two landmasses: Laurasia to the north, Gondwana to the south; this created more coastlines and shifted the continental climate from dry to humid, many of the arid deserts of the Triassic were replaced by lush rainforests.
On land, the fauna transitioned from the Triassic fauna, dominated by both dinosauromorph and crocodylomorph archosaurs, to one dominated by dinosaurs alone. The first birds appeared during the Jurassic, having evolved from a branch of theropod dinosaurs. Other major events include the appearance of the earliest lizards, the evolution of therian mammals, including primitive placentals. Crocodilians made the transition from a terrestrial to an aquatic mode of life; the oceans were inhabited by marine reptiles such as ichthyosaurs and plesiosaurs, while pterosaurs were the dominant flying vertebrates. The chronostratigraphic term "Jurassic" is directly linked to the Jura Mountains, a mountain range following the course of the France–Switzerland border. During a tour of the region in 1795, Alexander von Humboldt recognized the limestone dominated mountain range of the Jura Mountains as a separate formation that had not been included in the established stratigraphic system defined by Abraham Gottlob Werner, he named it "Jura-Kalkstein" in 1799.
The name "Jura" is derived from the Celtic root *jor via Gaulish *iuris "wooded mountain", borrowed into Latin as a place name, evolved into Juria and Jura. The Jurassic period is divided into three epochs: Early and Late. In stratigraphy, the Jurassic is divided into the Lower Jurassic, Middle Jurassic, Upper Jurassic series of rock formations known as Lias and Malm in Europe; the separation of the term Jurassic into three sections originated with Leopold von Buch. The faunal stages from youngest to oldest are: During the early Jurassic period, the supercontinent Pangaea broke up into the northern supercontinent Laurasia and the southern supercontinent Gondwana; the Jurassic North Atlantic Ocean was narrow, while the South Atlantic did not open until the following Cretaceous period, when Gondwana itself rifted apart. The Tethys Sea closed, the Neotethys basin appeared. Climates were warm, with no evidence of a glacier having appeared; as in the Triassic, there was no land over either pole, no extensive ice caps existed.
The Jurassic geological record is good in western Europe, where extensive marine sequences indicate a time when much of that future landmass was submerged under shallow tropical seas. In contrast, the North American Jurassic record is the poorest of the Mesozoic, with few outcrops at the surface. Though the epicontinental Sundance Sea left marine deposits in parts of the northern plains of the United States and Canada during the late Jurassic, most exposed sediments from this period are continental, such as the alluvial deposits of the Morrison Formation; the Jurassic was a time of calcite sea geochemistry in which low-magnesium calcite was the primary inorganic marine precipitate of calcium carbonate. Carbonate hardgrounds were thus common, along with calcitic ooids, calcitic cements, invertebrate faunas with dominantly calcitic skeletons; the first of several massive batholiths were emplaced in the northern American cordillera beginning in the mid-Jurassic, marking the Nevadan orogeny. Important Jurassic exposures are found in Russia, South America, Japan and the United Kingdom.
In Africa, Early Jurassic strata are distributed in a similar fashion to Late Triassic beds, with more common outcrops in the south and less common fossil beds which are predominated by tracks to the north. As the Jurassic proceeded and more iconic groups of dinosaurs like sauropods and ornithopods proliferated in Africa. Middle Jurassic strata are neither well studied in Africa. Late Jurassic strata are poorly represented apart from the spectacular Tendaguru fauna in Tanzania; the Late Jurassic life of Tendaguru is similar to that found in western North America's Morrison Formation. During the Jurassic period, the primary vertebrates living in the sea were marine reptiles; the latter include ichthyosaurs, which were at the peak of their diversity, plesiosaurs and marine crocodiles of the families Teleosauridae and Metriorhynchidae. Numerous turtles could be found in rivers. In the invertebrate world, several new groups appeared, including rudists (a reef-formi
.jpg)
