A chordate is an animal constituting the phylum Chordata. During some period of their life cycle, chordates possess a notochord, a dorsal nerve cord, pharyngeal slits, an endostyle, a post-anal tail: these five anatomical features define this phylum. Chordates are bilaterally symmetric; the Chordata and Ambulacraria together form the superphylum Deuterostomia. Chordates are divided into three subphyla: Vertebrata. There are extinct taxa such as the Vetulicolia. Hemichordata has been presented as a fourth chordate subphylum, but now is treated as a separate phylum: hemichordates and Echinodermata form the Ambulacraria, the sister phylum of the Chordates. Of the more than 65,000 living species of chordates, about half are bony fish that are members of the superclass Osteichthyes. Chordate fossils have been found from as early as the Cambrian explosion, 541 million years ago. Cladistically, vertebrates - chordates with the notochord replaced by a vertebral column during development - are considered to be a subgroup of the clade Craniata, which consists of chordates with a skull.
The Craniata and Tunicata compose the clade Olfactores. Chordates form a phylum of animals that are defined by having at some stage in their lives all of the following anatomical features: A notochord, a stiff rod of cartilage that extends along the inside of the body. Among the vertebrate sub-group of chordates the notochord develops into the spine, in wholly aquatic species this helps the animal to swim by flexing its tail. A dorsal neural tube. In fish and other vertebrates, this develops into the spinal cord, the main communications trunk of the nervous system. Pharyngeal slits; the pharynx is the part of the throat behind the mouth. In fish, the slits are modified to form gills, but in some other chordates they are part of a filter-feeding system that extracts particles of food from the water in which the animals live. Post-anal tail. A muscular tail that extends backwards behind the anus. An endostyle; this is a groove in the ventral wall of the pharynx. In filter-feeding species it produces mucus to gather food particles, which helps in transporting food to the esophagus.
It stores iodine, may be a precursor of the vertebrate thyroid gland. There are soft constraints that separate chordates from certain other biological lineages, but are not part of the formal definition: All chordates are deuterostomes; this means. All chordates are based on a bilateral body plan. All chordates are coelomates, have a fluid filled body cavity called a coelom with a complete lining called peritoneum derived from mesoderm; the following schema is from the third edition of Vertebrate Palaeontology. The invertebrate chordate classes are from Fishes of the World. While it is structured so as to reflect evolutionary relationships, it retains the traditional ranks used in Linnaean taxonomy. Phylum Chordata †Vetulicolia? Subphylum Cephalochordata – Class Leptocardii Clade Olfactores Subphylum Tunicata – Class Ascidiacea Class Thaliacea Class Appendicularia Class Sorberacea Subphylum Vertebrata Infraphylum incertae sedis Cyclostomata Superclass'Agnatha' paraphyletic Class Myxini Class Petromyzontida or Hyperoartia Class †Conodonta Class †Myllokunmingiida Class †Pteraspidomorphi Class †Thelodonti Class †Anaspida Class †Cephalaspidomorphi Infraphylum Gnathostomata Class †Placodermi Class Chondrichthyes Class †Acanthodii Superclass Osteichthyes Class Actinopterygii Class Sarcopterygii Superclass Tetrapoda Class Amphibia Class Sauropsida Class Synapsida Craniates, one of the three subdivisions of chordates, all have distinct skulls.
They include the hagfish. Michael J. Benton commented that "craniates are characterized by their heads, just as chordates, or all deuterostomes, are by their tails". Most craniates are vertebrates; these consist of a series of bony or cartilaginous cylindrical vertebrae with neural arches that protect the spinal cord, with projections that link the vertebrae. However hagfish have incomplete braincases and no vertebrae, are therefore not regarded as vertebrates, but as members of the craniates, the group from which vertebrates are thought to have evolved; however the cladistic exclusion of hagfish from the vertebrates is controversial, as they ma
The Smithsonian Institution, founded on August 10, 1846 "for the increase and diffusion of knowledge," is a group of museums and research centers administered by the Government of the United States. The institution is named after British scientist James Smithson. Organized as the "United States National Museum," that name ceased to exist as an administrative entity in 1967. Termed "the nation's attic" for its eclectic holdings of 154 million items, the Institution's nineteen museums, nine research centers, zoo include historical and architectural landmarks located in the District of Columbia. Additional facilities are located in Arizona, Massachusetts, New York City, Texas and Panama. More than 200 institutions and museums in 45 states, Puerto Rico, Panama are Smithsonian Affiliates; the Institution's thirty million annual visitors are admitted without charge. Its annual budget is around $1.2 billion with two-thirds coming from annual federal appropriations. Other funding comes from the Institution's endowment and corporate contributions, membership dues, earned retail and licensing revenue.
Institution publications include Air & Space magazines. The British scientist James Smithson left most of his wealth to his nephew Henry James Hungerford; when Hungerford died childless in 1835, the estate passed "to the United States of America, to found at Washington, under the name of the Smithsonian Institution, an Establishment for the increase & diffusion of knowledge among men", in accordance with Smithson's will. Congress accepted the legacy bequeathed to the nation, pledged the faith of the United States to the charitable trust on July 1, 1836; the American diplomat Richard Rush was dispatched to England by President Andrew Jackson to collect the bequest. Rush returned in August 1838 with 105 sacks containing 104,960 gold sovereigns. Once the money was in hand, eight years of Congressional haggling ensued over how to interpret Smithson's rather vague mandate "for the increase and diffusion of knowledge." The money was invested by the US Treasury in bonds issued by the state of Arkansas, which soon defaulted.
After heated debate, Massachusetts Representative John Quincy Adams persuaded Congress to restore the lost funds with interest and, despite designs on the money for other purposes, convinced his colleagues to preserve it for an institution of science and learning. On August 10, 1846, President James K. Polk signed the legislation that established the Smithsonian Institution as a trust instrumentality of the United States, to be administered by a Board of Regents and a Secretary of the Smithsonian. Though the Smithsonian's first Secretary, Joseph Henry, wanted the Institution to be a center for scientific research, it became the depository for various Washington and U. S. government collections. The United States Exploring Expedition by the U. S. Navy circumnavigated the globe between 1838 and 1842; the voyage amassed thousands of animal specimens, an herbarium of 50,000 plant specimens, diverse shells and minerals, tropical birds, jars of seawater, ethnographic artifacts from the South Pacific Ocean.
These specimens and artifacts became part of the Smithsonian collections, as did those collected by several military and civilian surveys of the American West, including the Mexican Boundary Survey and Pacific Railroad Surveys, which assembled many Native American artifacts and natural history specimens. In 1846, the regents developed a plan for weather observation; the Institution became a magnet for young scientists from 1857 to 1866, who formed a group called the Megatherium Club. The Smithsonian played a critical role as the U. S. partner institution in early bilateral scientific exchanges with the Academy of Sciences of Cuba. Construction began on the Smithsonian Institution Building in 1849. Designed by architect James Renwick Jr. its interiors were completed by general contractor Gilbert Cameron. The building opened in 1855; the Smithsonian's first expansion came with construction of the Arts and Industries Building in 1881. Congress had promised to build a new structure for the museum if the 1876 Philadelphia Centennial Exposition generated enough income.
It did, the building was designed by architects Adolf Cluss and Paul Schulze, based on original plans developed by Major General Montgomery C. Meigs of the United States Army Corps of Engineers, it opened in 1881. The National Zoological Park opened in 1889 to accommodate the Smithsonian's Department of Living Animals; the park was designed by landscape architect Frederick Law Olmsted. The National Museum of Natural History opened in June 1911 to accommodate the Smithsonian's United States National Museum, housed in the Castle and the Arts and Industries Building; this structure was designed by the D. C. architectural firm of Hornblower & Marshall. When Detroit philanthropist Charles Lang Freer donated his private collection to the Smithsonian and funds to build the museum to hold it, it was among the Smithsonian's first major donations from a private individual; the gallery opened in 1923. More than 40 years would pass before the next museum, the Museum of History and Technology, opened in 1964.
It was designed by the world-renowned firm of Mead & White. The Anacostia Community Museum, an "experimental store-front" museum created at the initiative of Smithsonian Secretary S. Dillon Ripley, opened in the Anacostia neighborhood of
The simians or Anthropoids are the monkeys, incl. apes, cladistically including: the New World monkeys or platyrrhines, the Catarrhine clade consisting of the Cercopithecidae and apes. The simians are sister to the tarsiers; the radiation occurred about 60 million years ago. 40 million years ago, simians from Afro-Arabia colonized South America, giving rise to the New World monkeys. The remaining simians split 25 million years ago into Cercopithecidae. In earlier classification, New World monkeys, Old World monkeys and humans—collectively known as simians or anthropoids—were grouped under Anthropoidea, while the strepsirrhines and tarsiers were grouped under the suborder "Prosimii". Under modern classification, the tarsiers and simians are grouped under the suborder Haplorhini while the strepsirrhines are placed in suborder Strepsirrhini. Strong genetic evidence for this is that five SINEs are common to all Haplorhines whilst absent in Strepsirrhines - one being coincidental between tarsiers and simians would be quite unlikely.
Despite this preferred taxonomic division, prosimian is still found in textbooks and the academic literature because of familiarity, a condition likened to the use of the metric system in the sciences and the use of customary units elsewhere in the United States. In Anthropoidea, evidence indicates that the Old and the New World primates went through parallel evolution. Primatology, paleoanthropology, other related fields are split on their usage of the synonymous infraorder names and Anthropoidea. According to Robert Hoffstetter, the term Simiiformes has priority over Anthropoidea because of the taxonomic term Simii by van der Hoeven, from which it is constructed, dates to 1833. In contrast, Anthropoidea by Mivart dates to 1864, while Simiiformes by Haeckel dates to 1866, leading to counterclaims of priority. Hoffstetter argued that Simiiformes is constructed like a proper infraorder name, whereas Anthropoidea ends in -oidea, reserved for superfamilies, he noted that Anthropoidea is too confused with "anthropoïdes", which translates to "apes" from several languages.
Extant simians are split into three distinct groups. The New World monkeys in parvorder Platyrrhini split from the rest of the simian line about 40 mya, leaving the parvorder Catarrhini occupying the Old World; this group split about 25 mya between the apes. There are some lines of extinct simian, either placed into Eosimiidae and sometimes in Amphipithecidae, thought to originate in the Early Oligocene. Additionally, Phileosimias is sometimes placed in the Eosimiidae and sometimes categorised separately; the following is the listing of the various simian families, their placement in the order Primates: Order Primates Suborder Strepsirrhini: non-tarsier prosimians Suborder Haplorhini: tarsiers + monkeys, including apes Infraorder Tarsiiformes Infraorder Simiiformes Parvorder Platyrrhini: New World monkeys Family Callitrichidae: marmosets and tamarins Family Cebidae: capuchins and squirrel monkeys Family Aotidae: night or owl monkeys Family Pitheciidae: titis and uakaris Family Atelidae: howler and woolly monkeys Parvorder Catarrhini Superfamily Cercopithecoidea Family Cercopithecidae Superfamily Hominoidea Family Hylobatidae: gibbons Family Hominidae: great apes, including humans †Amphipithecidae †EosimiidaeBelow is a cladogram with some of the extinct simian species with the more modern species emerging within the Eosimiidae.
The Simians originated in Asia. It is indicated how many million years ago the clades diverged into newer clades; the Ekgmowechashalidae are considered to be Strepsirrhini, not Haplorhini. A 2018 study places Eosimiidae as a sister to the crown haplorhini. In a section of their 2010 assessment of the evolution of anthropoids entitled'What Is An Anthropoid', Williams and Kirk set out a list of biological features that are common to all or most anthropoids, including genetic similarities, similarities in eye location and the muscles close to the eyes, internal similarities between ears, dental similarities, similarities on foot bone structure. Simia, Carl Linnaeus's original classification of these primates. BioMed Central Full text Gene conversion and purifying selection of a placenta-specific ERV-V envelope gene during simian evolution ADW Simiiformes Classification Taxonomy browser Late middle Eocene epoch of Libya yields earliest known radiation of African anthropoids Mouse-Sized Primates Shed Light on Human Origins
Homo erectus is a species of archaic humans that lived throughout most of the Pleistocene geological epoch. Its earliest fossil evidence dates to 1.8 million years ago. A debate regarding the classification and progeny of H. erectus in relation to Homo ergaster, is ongoing, with two major positions: 1) H. erectus is the same species as H. ergaster, thereby H. erectus is a direct ancestor of the hominins including Homo heidelbergensis, Homo antecessor, Homo neanderthalensis, Homo Denisova, Homo sapiens. Some paleoanthropologists consider H. ergaster to be a variety, that is, the "African" variety, of H. erectus. H. Erectus became extinct throughout its range in Africa and Asia, but developed into derived species, notably Homo heidelbergensis; as a chronospecies, the time of its disappearance is thus a matter of contention. The species name proposed in 1950 defines Java Man as the type specimen. Since there has been a trend in palaeoanthropology of reducing the number of proposed species of Homo, to the point where H. erectus includes all early forms of Homo sufficiently derived from H. habilis and distinct from early H. heidelbergensis.
In this wider sense, H. erectus had been replaced by H. heidelbergensis by about 300,000 years ago, with possible late survival in Java as late as 70,000 years ago. The discovery of the morphologically divergent Dmanisi skull 5 in 2013 has reinforced the trend of subsuming fossils given separate species names under H. erectus considered as a wide-ranging, polymorphous species. Thus, H. ergaster is now well within the accepted morphological range of H. erectus, it has been suggested that H. rudolfensis and H. habilis should be considered early varieties of H. erectus. The Dutch anatomist Eugène Dubois, inspired by Darwin's theory of evolution as it applied to humanity, set out in 1886 for Asia to find a human ancestor. In 1891–92, his team discovered first a tooth a skullcap, a femur of a human fossil on the island of Java, Dutch East Indies. Excavated from the bank of the Solo River at Trinil, in East Java, he first allocated the material to a genus of fossil chimpanzees as Anthropopithecus erectus the following year assigned his species to a new genus as Pithecanthropus erectus —from the Greek πίθηκος and ἄνθρωπος —based on the proposal that the femur suggested that the creature had been bipedal, like Homo sapiens.
Dubois' 1891 find was the first fossil of a Homo-species found as result of a directed expedition and search. The Java fossil from Indonesia aroused much public interest, it was dubbed by the popular press as Java Man. Most of the spectacular discoveries of H. erectus next took place at the Zhoukoudian Project, now known as the Peking Man site, in Zhoukoudian, China. This site was first discovered by Johan Gunnar Andersson in 1921 and was first excavated in 1921, produced two human teeth. Davidson Black's initial description of a lower molar as belonging to a unknown species prompted publicized interest. Extensive excavations followed, which altogether uncovered 200 human fossils from more than 40 individuals including five nearly complete skullcaps. Franz Weidenreich provided much of the detailed description of this material in several monographs published in the journal Palaeontologica Sinica. Nearly all of the original specimens were lost during World War II. Similarities between Java Man and Peking Man led Ernst Mayr to rename both Homo erectus in 1950.
Throughout much of the 20th century, anthropologists debated the role of H. erectus in human evolution. Early in the century, due in part to the discoveries at Java and Zhoukoudian, the belief that modern humans first evolved in Asia was accepted. A few naturalists—Charles Darwin most prominent among them—theorized that humans' earliest ancestors were African: Darwin pointed out that chimpanzees and gorillas, humans' closest relatives and exist only in Africa; the derivation of the genus Homo from Australopithecina took place in East Africa after 3 million years ago. The inclusion of species dated to just before 2 million years ago, Homo habilis and Homo rudolfensis, into Homo is somewhat contentious; as H. habilis appears to have coexisted with H. ergaster/erectus for a substantial period after 2 Mya, it has been proposed that ergaster may not be directly derived from habilis. Homo erectus emerged about 2 million years ago. Fossils dated close to 1.8 million years ago have been found both in
The Hominidae, whose members are known as great apes or hominids, are a taxonomic family of primates that includes eight extant species in four genera: Pongo, the Bornean and Tapanuli orangutan. Several revisions in classifying the great apes have caused the use of the term "hominid" to vary over time, its original meaning referred only to their closest extinct relatives. That restrictive meaning has now been assumed by the term "hominin", which comprises all members of the human clade after the split from the chimpanzees; the current, 21st-century meaning of "hominid" includes all the great apes including humans. Usage still varies and some scientists and laypersons still use "hominid" in the original restrictive sense. Within the taxon Hominidae, a number of extant and known extinct, that is, genera are grouped with the humans and gorillas in the subfamily Homininae; the most recent common ancestor of all Hominidae lived 14 million years ago, when the ancestors of the orangutans speciated from the ancestral line of the other three genera.
Those ancestors of the family Hominidae had speciated from the family Hylobatidae 15 million to 20 million years ago. In the early Miocene, about 22 million years ago, there were many species of arboreally adapted primitive catarrhines from East Africa. Fossils at 20 million years ago include fragments attributed to Victoriapithecus, the earliest Old World monkey. Among the genera thought to be in the ape lineage leading up to 13 million years ago are Proconsul, Dendropithecus, Nacholapithecus, Nyanzapithecus, Afropithecus and Kenyapithecus, all from East Africa. At sites far distant from East Africa, the presence of other generalized non-cercopithecids, that is, non-monkey primates, of middle Miocene age—Otavipithecus from cave deposits in Namibia, Pierolapithecus and Dryopithecus from France and Austria—is further evidence of a wide diversity of ancestral ape forms across Africa and the Mediterranean basin during the warm and equable climatic regimes of the early and middle Miocene; the most recent of these far-flung Miocene apes is Oreopithecus, from the fossil-rich coal beds in northern Italy and dated to 9 million years ago.
Molecular evidence indicates that the lineage of gibbons, the lesser apes, diverged from that of the great apes some 18–12 million years ago, that of orangutans diverged from the other great apes at about 12 million years. There are no fossils that document the ancestry of gibbons, which may have originated in a still-unknown South East Asian hominoid population. Species close to the last common ancestor of gorillas and humans may be represented by Nakalipithecus fossils found in Kenya and Ouranopithecus found in Greece. Molecular evidence suggests that between 8 and 4 million years ago, first the gorillas, the chimpanzees split off from the line leading to the humans. Human DNA is 98.4% identical to that of chimpanzees when comparing single nucleotide polymorphisms. The fossil record, however, of gorillas and chimpanzees is limited. Other hominins adapted to the drier environments outside the African equatorial belt; the wet equatorial belt contracted after about 8 million years ago, there is little fossil evidence for the divergence of the hominin lineage from that of gorillas and chimpanzees—which split was thought to have occurred around that time.
The earliest fossils argued by some to belong to the human lineage are Sahelanthropus tchadensis and Orrorin tugenensis, followed by Ardipithecus, with species Ar. kadabba and Ar. ramidus. The classification of the great apes has been revised several times in the last few decades; the original meaning of the term referred to only humans and their closest relatives—what is now the modern meaning of the term "hominin". The meaning of the taxon Hominidae changed leading to a different usage of "hominid" that today includes all the great apes including humans; the term hominid is confused with a number of similar words: A hominoid called an ape, is a member of the superfamily Hominoidea: extant members are the gibbons and the hominids. A hominid is a member of the family Hominidae, the great apes: orangutans, gorillas and humans. A hominine is a member of the subfamily Homininae: gorillas and humans. A hominin is a member of the tribe Hominini: humans. A homininan, following a suggestion by Wood and Richmond, would be a member of the subtribe Homin
Binomial nomenclature called binominal nomenclature or binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, both of which use Latin grammatical forms, although they can be based on words from other languages. Such a name is called a binomen, binominal name or a scientific name; the first part of the name – the generic name – identifies the genus to which the species belongs, while the second part – the specific name or specific epithet – identifies the species within the genus. For example, humans belong within this genus to the species Homo sapiens. Tyrannosaurus rex is the most known binomial; the formal introduction of this system of naming species is credited to Carl Linnaeus beginning with his work Species Plantarum in 1753. But Gaspard Bauhin, in as early as 1623, had introduced in his book Pinax theatri botanici many names of genera that were adopted by Linnaeus; the application of binomial nomenclature is now governed by various internationally agreed codes of rules, of which the two most important are the International Code of Zoological Nomenclature for animals and the International Code of Nomenclature for algae and plants.
Although the general principles underlying binomial nomenclature are common to these two codes, there are some differences, both in the terminology they use and in their precise rules. In modern usage, the first letter of the first part of the name, the genus, is always capitalized in writing, while that of the second part is not when derived from a proper noun such as the name of a person or place. Both parts are italicized when a binomial name occurs in normal text, thus the binomial name of the annual phlox is now written as Phlox drummondii. In scientific works, the authority for a binomial name is given, at least when it is first mentioned, the date of publication may be specified. In zoology "Patella vulgata Linnaeus, 1758"; the name "Linnaeus" tells the reader who it was that first published a description and name for this species of limpet. "Passer domesticus". The original name given by Linnaeus was Fringilla domestica; the ICZN does not require that the name of the person who changed the genus be given, nor the date on which the change was made, although nomenclatorial catalogs include such information.
In botany "Amaranthus retroflexus L." – "L." is the standard abbreviation used in botany for "Linnaeus". "Hyacinthoides italica Rothm. – Linnaeus first named this bluebell species Scilla italica. The name is composed of two word-forming elements: "bi", a Latin prefix for two, "-nomial", relating to a term or terms; the word "binomium" was used in Medieval Latin to mean a two-term expression in mathematics. Prior to the adoption of the modern binomial system of naming species, a scientific name consisted of a generic name combined with a specific name, from one to several words long. Together they formed a system of polynomial nomenclature; these names had two separate functions. First, to designate or label the species, second, to be a diagnosis or description. In a simple genus, containing only two species, it was easy to tell them apart with a one-word genus and a one-word specific name; such "polynomial names" may sometimes look like binomials, but are different. For example, Gerard's herbal describes various kinds of spiderwort: "The first is called Phalangium ramosum, Branched Spiderwort.
The other... is aptly termed Phalangium Ephemerum Virginianum, Soon-Fading Spiderwort of Virginia". The Latin phrases are short descriptions, rather than identifying labels; the Bauhins, in particular Caspar Bauhin, took some important steps towards the binomial system, by pruning the Latin descriptions, in many cases to two words. The adoption by biologists of a system of binomial nomenclature is due to Swedish botanist and physician Carl von Linné, more known by his Latinized name Carl Linnaeus, it was in his 1753 Species Plantarum that he first began using a one-word "trivial name" together with a generic name in a system of binomial nomenclature. This trivial name is what is now known as specific name; the Bauhins' genus names were retained in many of these, but the descriptive part was reduced to a single word. Linnaeus's trivial names introduced an important new idea, namely that the function of a name could be to give a species a unique label; this meant. Thus Gerard's Phalangium ephemerum virginianum became Tradescantia virgi
Acheulean, from the French acheuléen, is an archaeological industry of stone tool manufacture characterized by distinctive oval and pear-shaped "hand-axes" associated with Homo erectus and derived species such as Homo heidelbergensis. Acheulean tools were produced during the Lower Palaeolithic era across Africa and much of West Asia, South Asia, Europe, are found with Homo erectus remains, it is thought that Acheulean technologies first developed about 1.76 million years ago, derived from the more primitive Oldowan technology associated with Homo habilis. The Acheulean includes at least the early part of the Middle Paleolithic, its end is not well defined, depending on whether Sangoan is included, it may be taken to last until as late as 130,000 years ago. In Europe and Western Asia, early Neanderthals adopted Achaeulean technology, transitioning to Mousterian by about 160,000 years ago; the type site for the Acheulean is Saint-Acheul, a suburb of Amiens, the capital of the Somme department in Picardy, where artifacts were found in 1859.
John Frere is credited as being the first to suggest a ancient date for Acheulean hand-axes. In 1797, he sent two examples to the Royal Academy in London from Hoxne in Suffolk, he had found them in prehistoric lake deposits along with the bones of extinct animals and concluded that they were made by people "who had not the use of metals" and that they belonged to a "very ancient period indeed beyond the present world". His ideas were, ignored by his contemporaries, who subscribed to a pre-Darwinian view of human evolution. Jacques Boucher de Crèvecœur de Perthes, working between 1836 and 1846, collected further examples of hand-axes and fossilised animal bone from the gravel river terraces of the Somme near Abbeville in northern France. Again, his theories attributing great antiquity to the finds were spurned by his colleagues, until one of de Perthe's main opponents, Dr Marcel Jérôme Rigollot, began finding more tools near Saint Acheul. Following visits to both Abbeville and Saint Acheul by the geologist Joseph Prestwich, the age of the tools was accepted.
In 1872, Louis Laurent Gabriel de Mortillet described the characteristic hand-axe tools as belonging to L'Epoque de St Acheul. The industry was renamed as the Acheulean in 1925. Providing calendrical dates and ordered chronological sequences in the study of early stone tool manufacture is accomplished through one or more geological techniques, such as radiometric dating potassium-argon dating, magnetostratigraphy. From the Konso Formation of Ethiopia, Acheulean hand-axes are dated to about 1.5 million years ago using radiometric dating of deposits containing volcanic ashes. Acheulean tools in South Asia have been found to be dated as far as 1.5 million years ago. However, the earliest accepted examples of the Acheulean known come from the West Turkana region of Kenya and were first described by a French-led archaeology team; these particular Acheulean tools were dated through the method of magnetostratigraphy to about 1.76 million years ago, making them the oldest not only in Africa but the world.
The earliest user of Acheulean tools was Homo ergaster, who first appeared about 1.8 million years ago. Not all researchers use this formal name, instead prefer to call these users early Homo erectus. From geological dating of sedimentary deposits, it appears that the Acheulean originated in Africa and spread to Asian, Middle Eastern, European areas sometime between 1.5 million years ago and about 800 thousand years ago. In individual regions, this dating can be refined; however more recent research demonstrated that hand-axes from Spain were made more than 900,000 years ago. Relative dating techniques suggest that Acheulean tools followed on from earlier, cruder tool-making methods, but there is considerable chronological overlap in early prehistoric stone-working industries, with evidence in some regions that Acheulean tool-using groups were contemporary with other, less sophisticated industries such as the Clactonian and later with the more sophisticated Mousterian, as well, it is therefore important not to see the Acheulean as a neatly defined period or one that happened as part of a clear sequence but as one tool-making technique that flourished well in early prehistory.
The enormous geographic spread of Acheulean techniques makes the name unwieldy as it represents numerous regional variations on a similar theme. The term Acheulean does not represent a common culture in the modern sense, rather it is a basic method for making stone tools, shared across much of the Old World; the earliest Acheulean assemblages contain numerous Oldowan-style flakes and core forms and it is certain that the Acheulean developed from this older industry. These industries are known as the Developed Oldowan and are certainly transitional between the Oldowan and Acheulean. In the four divisions of prehistoric stone-working, Acheulean artefacts are classified as Mode 2, meaning they are more advanced than the Mode 1 tools of the Clactonian or Oldowan/Abbevillian industries but lacking the sophistication of the Mode 3 Middle Palaeolithic technology, exemplified by the Mousterian industry; the Mode 1 industries created rough flake tools by hitting a suitable stone with a hammerstone. The resulting flake that broke off would have a natural sharp edge for cutting and could afterwards be sharpened further by striking another smaller flake from the edge if necessary