In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring by sexual reproduction. Other ways of defining species include their karyotype, DNA sequence, behaviour or ecological niche. In addition, paleontologists use the concept of the chronospecies since fossil reproduction cannot be examined. While these definitions may seem adequate, when looked at more they represent problematic species concepts. For example, the boundaries between related species become unclear with hybridisation, in a species complex of hundreds of similar microspecies, in a ring species. Among organisms that reproduce only asexually, the concept of a reproductive species breaks down, each clone is a microspecies. All species are given a two-part name, a "binomial"; the first part of a binomial is the genus.
The second part is called the specific epithet. For example, Boa constrictor is one of four species of the genus Boa. None of these is satisfactory definitions, but scientists and conservationists need a species definition which allows them to work, regardless of the theoretical difficulties. If species were fixed and distinct from one another, there would be no problem, but evolutionary processes cause species to change continually, to grade into one another. Species were seen from the time of Aristotle until the 18th century as fixed kinds that could be arranged in a hierarchy, the great chain of being. In the 19th century, biologists grasped. Charles Darwin's 1859 book The Origin of Species explained how species could arise by natural selection; that understanding was extended in the 20th century through genetics and population ecology. Genetic variability arises from mutations and recombination, while organisms themselves are mobile, leading to geographical isolation and genetic drift with varying selection pressures.
Genes can sometimes be exchanged between species by horizontal gene transfer. Viruses are a special case, driven by a balance of mutation and selection, can be treated as quasispecies. Biologists and taxonomists have made many attempts to define species, beginning from morphology and moving towards genetics. Early taxonomists such as Linnaeus had no option but to describe what they saw: this was formalised as the typological or morphological species concept. Ernst Mayr emphasised reproductive isolation, but this, like other species concepts, is hard or impossible to test. Biologists have tried to refine Mayr's definition with the recognition and cohesion concepts, among others. Many of the concepts are quite similar or overlap, so they are not easy to count: the biologist R. L. Mayden recorded about 24 concepts, the philosopher of science John Wilkins counted 26. Wilkins further grouped the species concepts into seven basic kinds of concepts: agamospecies for asexual organisms biospecies for reproductively isolated sexual organisms ecospecies based on ecological niches evolutionary species based on lineage genetic species based on gene pool morphospecies based on form or phenotype and taxonomic species, a species as determined by a taxonomist.
A typological species is a group of organisms in which individuals conform to certain fixed properties, so that pre-literate people recognise the same taxon as do modern taxonomists. The clusters of variations or phenotypes within specimens would differentiate the species; this method was used as a "classical" method of determining species, such as with Linnaeus early in evolutionary theory. However, different phenotypes are not different species. Species named in this manner are called morphospecies. In the 1970s, Robert R. Sokal, Theodore J. Crovello and Peter Sneath proposed a variation on this, a phenetic species, defined as a set of organisms with a similar phenotype to each other, but a different phenotype from other sets of organisms, it differs from the morphological species concept in including a numerical measure of distance or similarity to cluster entities based on multivariate comparisons of a reasonably large number of phenotypic traits. A mate-recognition species is a group of sexually reproducing organisms that recognize one another as potential mates.
Expanding on this to allow for post-mating isolation, a cohesion species is the most inclusive population of individuals having the potential for phenotypic cohesion through intrinsic cohesion mechanisms. A further development of the recognition concept is provided by the biosemiotic concept of species. In microbiology, genes can move even between distantly related bacteria extending to the whole bacterial domain; as a rule of thumb, microbiologists have assumed that kinds of Bacteria or Archaea with 16S ribosomal RNA gene sequences more similar than 97% to each other need to be checked by DNA-DNA hybridisation to decide if they belong to the same species or not. This concept was narrowed in 2006 to a similarity of 98.7%. DNA-DNA hybri
A trace fossil ichnofossil, is a geological record of biological activity. Ichnology is the study of such traces, is the work of ichnologists. Trace fossils may consist of impressions made on or in the substrate by an organism: for example, borings, urolites and feeding marks, root cavities; the term in its broadest sense includes the remains of other organic material produced by an organism — for example coprolites or chemical markers — or sedimentological structures produced by biological means - for example, stromatolites. Trace fossils contrast with body fossils, which are the fossilized remains of parts of organisms' bodies altered by chemical activity or mineralization. Sedimentary structures, for example those produced by empty shells rolling along the sea floor, are not produced through the behaviour of an organism and not considered trace fossils; the study of traces - ichnology - divides into paleoichnology, or the study of trace fossils, neoichnology, the study of modern traces. Ichnological science offers many challenges, as most traces reflect the behaviour — not the biological affinity — of their makers.
Accordingly, researchers classify trace fossils into form genera, based on their appearance and on the implied behaviour, or ethology, of their makers. Traces are better known in their fossilised form than in modern sediments; this makes it difficult to interpret some fossils by comparing them with modern traces though they may be extant or common. The main difficulties in accessing extant burrows stem from finding them in consolidated sediment, being able to access those formed in deeper water. Trace fossils are best preserved in sandstones, they may be found in shales and limestones. Trace fossils are difficult or impossible to assign to a specific maker. Only in rare occasions are the makers found in association with their tracks. Further different organisms may produce identical tracks. Therefore, conventional taxonomy is not applicable, a comprehensive form of taxonomy has been erected. At the highest level of the classification, five behavioral modes are recognized: Domichnia, dwelling structures reflecting the life position of the organism that created it.
Fodinichnia, three-dimensional structures left by animals which eat their way through sediment, such as deposit feeders. Fossils are further classified into form genera, a few of which are subdivided to a "species" level. Classification is based on shape and implied behavioural mode. To keep body and trace fossils nomenclatorially separate, ichnospecies are erected for trace fossils. Ichnotaxa are classified somewhat differently in zoological nomenclature than taxa based on body fossils. Examples include: Late Cambrian trace fossils from intertidal settings include Protichnites and Climactichnites, amongst others Mesozoic dinosaur footprints including ichnogenera such as Grallator and Anomoepus Triassic to Recent termite mounds, which can encompass several square kilometers of sediment Trace fossils are important paleoecological and paleoenvironmental indicators, because they are preserved in situ, or in the life position of the organism that made them; because identical fossils can be created by a range of different organisms, trace fossils can only reliably inform us of two things: the consistency of the sediment at the time of its deposition, the energy level of the depositional environment.
Attempts to deduce such traits as whether a deposit is marine or non-marine have been made, but shown to be unreliable. Trace fossils provide us with indirect evidence of life in the past, such as the footprints, burrows and feces left behind by animals, rather than the preserved remains of the body of the actual animal itself. Unlike most other fossils, which are produced only after the death of the organism concerned, trace fossils provide us with a record of the activity of an organism during its lifetime. Trace fossils are formed by organisms performing the functions of their everyday life, such as walking, burrowing, boring, or feeding. Tetrapod footprints, worm trails and the burrows made by clams and arthropods are all trace fossils; the most spectacular trace fossils are the huge, three-toed footprints produced by dinosaurs and related archosaurs. These imprints give scientists clues as to. Although the skeletons of dinosaurs can be reconstructed, only their fossilized footprints can determine how they stood and walked.
Such tracks can tell much about the gait of the animal which made them, what its stride was, whether or not the front limbs touched the ground. However, most trace fossils are rather less conspicuous, such as the trails made by segmented worms or nematodes; some of these worm castings are the only fossil record. Fossil footprints made by tetrapod vertebrates are difficult to identify to a particular species of animal, but they can provide valuable information such as the speed and behavior of the organism that made them; such trace fossils are formed when amphibians, mammals or birds walked across soft mud or sand which hardened sufficiently to retain the impressions before the next layer of sedimen
In typography, italic type is a cursive font based on a stylised form of calligraphic handwriting. Owing to the influence from calligraphy, italics slant to the right. Italics are a way to emphasise key points in a printed text, to identify many types of creative works, or, when quoting a speaker, a way to show which words they stressed. One manual of English usage described italics as "the print equivalent of underlining"; the name comes from the fact that calligraphy-inspired typefaces were first designed in Italy, to replace documents traditionally written in a handwriting style called chancery hand. Aldus Manutius and Ludovico Arrighi were the main type designers involved in this process at the time. Different glyph shapes from Roman type are used – another influence from calligraphy – and upper-case letters may have swashes, flourishes inspired by ornate calligraphy. An alternative is oblique type, in which the type is slanted but the letterforms do not change shape: this less elaborate approach is used by many sans-serif typefaces.
Italic type was first used by Aldus Manutius and his press in Venice in 1500. Manutius intended his italic type to be used not for emphasis but for the text of small carried editions of popular books, replicating the style of handwritten manuscripts of the period; the choice of using italic type, rather than the roman type in general use at the time, was made to suggest informality in editions designed for leisure reading. Manutius' italic type was cut by his punchcutter Francesco Griffo, it replicated handwriting of the period following from the style of Niccolò de' Niccoli even Manutius' own. The first use in a complete volume was a 1501 edition of Virgil dedicated to Italy, although it had been used in the frontispiece of a 1500 edition of Catherine of Siena's letters. In 1501, Aldus wrote to his friend Scipio: We have printed, are now publishing, the Satires of Juvenal and Persius in a small format, so that they may more conveniently be held in the hand and learned by heart by everyone. Manutius' italic was different in some ways from modern italics, being conceived for the specific use of replicating the layout of contemporary calligraphers like Pomponio Leto and Bartolomeo Sanvito.
The capital letters were upright capitals on the model of Roman square capitals, shorter than the ascending lower-case italic letters, were used at the start of each line followed by a clear space before the first lower-case letter. While modern italics are more condensed than roman types, historian Harry Carter describes Manutius' italic as about the same width as roman type. To replicate handwriting, Griffo cut at least sixty-five tied letters in the Aldine Dante and Virgil of 1501. Italic typefaces of the following century reduced numbers of ligatures. Italic type became popular and was imitated; the Venetian Senate gave Aldus exclusive right to its use, a patent confirmed by three successive Popes, but it was counterfeited as early as 1502. Griffo, who had left Venice in a business dispute, cut a version for printer Girolamo Soncino, other copies appeared in Italy and in Lyons; the Italians called the character Aldino. Italics spread rapidly; some printers of Northern Europe used home-made supplements to add characters not used in Italian, or mated it to alternative capitals, including Gothic ones.
Besides imitations of Griffo's italic and its derivatives, a second wave appeared of "chancery" italics, most popular in Italy, which Vervliet describes as being based on "a more deliberate and formal handwriting longer ascenders and descenders, sometimes with curved or bulbous terminals, only available in the bigger sizes." Chancery italics were introduced around 1524 by Arrighi, a calligrapher and author of a calligraphy textbook who began a career as a printer in Rome, by Giovanni Antonio Tagliente of Venice, with imitations appearing in France by 1528. Chancery italics faded as a style over the course of the sixteenth century, although revivals were made beginning in the twentieth century. Chancery italics may have backward-pointing serifs or round terminals pointing forwards on the ascenders. Italic capitals with a slope were introduced in the sixteenth century; the first printer known to have used them was Johann or Johannes Singriener in Vienna in 1524, the practice spread to Germany and Belgium.
Influential in the switch to sloped capitals as a general practice was Robert Granjon, a prolific and precise French punchcutter renowned for his skill in cutting italics. Vervliet comments that among punchcutters in France "the main name associated with the change is Granjon's."The evolution of use of italic to show emphasis happened in the sixteenth century and was a clear norm by the seventeenth. The trend of presenting types as matching in typefounders' specimens developed over this period. Italics developed stylistically over the following centuries, tracking changing tastes in calligraphy and type design. One major development that became popular from the end of the seventeenth century was a switch to an open form h matching the n, a development seen in the Romain du roi type of the 1690s, replacing the folded, closed-form h of sixteenth- and seventeenth-century italics, sometimes simplification of the entrance stroke. Here is an example of normal and true italics text: Here is the same text as oblique text: True italic styles are traditi
A makhtesh (Hebrew: מַכְתֵּשׁ, plural: מַכְתְּשִׁים is a geological landform considered typical for the Negev desert of Israel and the Sinai peninsula of Egypt. A makhtesh has steep walls of resistant rock surrounding a deep closed valley, drained by a single wadi; the valleys have limited vegetation and soil, containing a variety of different colored rocks and diverse fauna and flora. The best known and largest makhtesh is Makhtesh Ramon. Although referred to as "craters", these formations are "erosion cirques". Craters are formed by the impact of a meteor or volcanic eruption, whereas makhteshim are created by erosion; the word makhtesh is the Hebrew word for a mortar grinder. The geological landform was given this name because of its similarity to a grinding bowl. Where a hard outer layer of rock covers softer rocks, erosion removes the softer minerals quickly, they are washed away from under the harder rock; the harder rocks collapse under their own weight, a crater-like valley structure is formed.
In Negev and Sinai makhteshim, the hard rocks are limestone and dolomite, while the inner softer rocks are chalk or sandstone. The center of the Negev is dominated by northeast-southwest anticlinal ridges; the crests of four ridges host five deep valleys surrounded by steep walls. The upper half consists of hard limestone and dolomite, the bottom of friable sandstone; each valley, known as a makhtesh, is drained by a narrow river bed. The Negev has five makhteshim: Makhtesh Ramon, Makhtesh Gadol, Makhtesh Katan, two small makhteshim on Mount Arif, south of Makhtesh Ramon. Makhtesh Ramon is exceptional, it is the largest makhtesh at over 40 km long, 2 -- 10 over 500 m deep. The rocks in this makhtesh contain thousands of ammonite fossils, as well as volcanic and metamorphic rocks. Makhtesh Gadol. At the time of naming, Makhtesh Ramon was uncharted, so this was thought to be the largest makhtesh, at 5 km by 10 km. Makhtesh Katan is the smallest major makhtesh at 5 km by 7 km and was charted in 1942 by Jewish explorers.
The two makhteshim in Sinai, have no names for the basin, but their walls have several names including Jabal al-Manzur or Gebel Maghara. Many similar geological formations are found in Wadi Rum in southern Jordan. Mazor and Krasnov, editors "The Makhteshim Country - a Laboratory of Nature". Pensoft Publishers, Sofia, 2001, 411 pages. ISBN 954-642-135-9
Bird ichnology is the study of avian life traces in ornithology and paleontology. Such life traces can include footprints, nests and coproliths. Scientists gain insight about the diversity of birds by studying such evidence. Ichnofossils are important for clarifying the evolution and prehistoric diversity of taxa; these cannot be associated with a particular genus, let alone species of bird, as hardly they are associated with fossil bones. But it is possible to group them into ichnotaxa based on their morphology. In practice, the details of shape that reveal the birds' behavior or biologic affinity are given more weight in ichnologic classification; these fossil traces of birds are sometimes hard to interpret especially when they are from the Mesozoic when the birds' dinosaurian relatives were still in existence. Nests at least of Neornithes are quite easy to identify as such due to the unique structures of their eggshells. Mesozoic fossil footprints are hardest to attribute. "Proto-bird" and related theropod feet were much alike.
Under the creationist dogma, scientists would believe that e.g. rheas had been around for all eternity. In the Jurassic and Early Cretaceous, juvenile non-avian theropods left birdlike footprints. Towards the end of the Cretaceous, the tracks of aquatic birds are recognizable due to the presence of webbing between the toes. However, giant flightless birds existed by that time, as evidenced by Gargantuavis; such footprints may resemble those of non-avian theropod or ornithopod dinosaurs. Among the former, the Ornithomimiformes were convergent to ratites in many respects, including the feet, it is impossible to tell if some large bird-like footprints from the Late Cretaceous are from an ornithomimiform or a giant bird, without associated bone material. There exist documented tracks that appear avian since the Late Triassic, by some 55 million years predating the first proper evidence that birdlike theropods were present; the Late Triassic and early-mid Jurassic tracks have been assigned to the ichnogenera Trisauropodiscus and Aquatilavipes.
Few scientists would go as far though to consider these traces evidence that birds evolved much earlier than believed, not from theropod dinosaurs as per today's mainstream opinion. In fact, it seems that the initial dating of these ancient bird-like tracks was in error, they seem to date from a much time when modern birds were known from bone fossils. Footprints of at least Neornithes can be distinguished by several features: if a hallux is present, it is directed straight backwards or nearly so; the second to fourth toes have a wide angle between them due to Neornithes having a fused tarsometatarsus they have no heel pads It is notable that Heterodontosauridae are known from the localities and times when the first avian-looking footprints started to appear. These small ornithopod dinosaurs were unbirdlike, except for their ornithischian pelvis and a tarsometatarsus convergent to that of Enantiornithes. Though some details remain unresolved, it is far more plausible that Trisauropodiscus etc. were made by a Heterodontosaurus-like animal rather than some sort of bird.
†Trisauropodiscus Avian? Non-avian theropod? Heterodontosaurid?†Archaeornithipus No hallux. Toes long, small webs. Avian: Patagopteryx? shorebird?†Fuscinapedis 35 × 35 cm. Toes long, wide. Avian: giant flightless bird?†Goseongornipes – Geongsangornipes is lapsus4-4.5 × 3-3.5 cm. Toes long, thin, T3-T4 small webs, T2 shorter. Avian: shorebird†Jindongornipes 6.5–7.5 × 5–6 cm. Toes long, unwebbed, T2 shorter. Avian: shorebird†Koreanaornis 2.5–3.5 × 2.5-3 cm. Toes long, unwebbed. Avian: shorebird†Ichnogen. Indet. 2.3 × 3.5 cm. Toes narrow, unwebbed, T2+T4 shorter. Avian? perching bird?†Magnoavipes 25 × 20 cm. Toes long thin. Avian?†Pullornipes 3.3–5.1 × 3.3–4.7 cm. Toes long, unwebbed. Avian
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
An artifact, or artefact, is something made or given shape by humans, such as a tool or a work of art an object of archaeological interest. In archaeology, the word has become a term of particular nuance and is defined as: an object recovered by archaeological endeavor, which may be a cultural artifact having cultural interest. However, modern archaeologists take care to distinguish material culture from ethnicity, more complex, as expressed by Carol Kramer in the dictum "pots are not people". Examples include stone tools, pottery vessels, metal objects such as weapons, items of personal adornment such as buttons and clothing. Bones that show signs of human modification are examples. Natural objects, such as fire cracked rocks from a hearth or plant material used for food, are classified by archeologists as ecofacts rather than as artifacts. Artifacts can come from any archaeological context or source such as: Buried along with a body From any feature such as a midden or other domestic setting Votive offerings Hoards, such as at wellsArtifacts are distinguished from the main body of the archaeological record such as stratigraphic features, which are non-portable remains of human activity, such as hearths, deposits, trenches or similar remains, from biofacts or ecofacts, which are objects of archaeological interest made by other organisms, such as seeds or animal bone.
Natural objects that humans have moved but not changed are called manuports. Examples include seashells moved inland, or rounded pebbles placed away from the water action that made them; these distinctions are blurred. For instance, a bone removed from an animal carcass is a biofact, but a bone carved into a useful implement is an artifact. There can be debate over early stone objects that could be either crude artifacts or occurring and happen to resemble early objects made by early humans or Homo sapiens, it can be difficult to distinguish the differences between actual man-made lithic artifacts and geofacts – occurring lithics that resemble man-made tools. It is possible to authenticate artifacts by examining the general characteristics attributed to man-made tools and local characteristics of the site. In ethnography and archaeology, a category of "ancestral artifact" has been proposed, defined as "any object of natural raw material made by a people following a lifestyle based on foraging and/or basic agriculture or pastoralism".
Artifact Collection at the Royal Military College of Canada Museum in Kingston, Ontario