Homininae called "African hominids" or "African apes", is a subfamily of Hominidae. It includes two tribes, with their extant as well as extinct species: 1) the Hominini tribe ―and 2) the Gorillini tribe. Alternatively, the genus Pan is sometimes considered to belong to Panini. Homininae comprises all hominids; the Homininae cladogram has three main branches, which lead to gorillas, to humans and chimpanzees via the tribe Hominini and subtribes Hominina and Panina. There are two living species of Panina and two living species of gorillas, but only one extant human species. Traces of hypothetical Homo species, including Homo floresiensis and Homo denisova, have been found with dates as recent as 40,000 years ago. Organisms in this subfamily are described as hominine or hominines; until 1980, the family Hominidae meant humans only. Discoveries led to revised classifications, with the great apes united with humans as members of family Hominidae Further discoveries indicated that gorillas and chimpanzees are more related to humans than they are to orangutans, leading to their placement in subfamily Homininae as well.
The subfamily Homininae can be further subdivided into three branches: the tribe Gorillini, the tribe Hominini with subtribes Panina and Hominina. The Late Miocene fossil Nakalipithecus nakayamai, described in 2007, is a basal member of this clade, as is its contemporary Ouranopithecus, their existence suggests that the Homininae tribes diverged not earlier than about 8 million years ago. Today and gorillas live in tropical forests with acid soils that preserve fossils. Although no fossil gorillas have been reported, four chimpanzee teeth about 500,000 years old have been discovered in the East-African rift valley, where many fossils from the human lineage have been found; this shows. Homininae Udabnopithecus† Udabnopithecus garedziensis Tribe Dryopithecini† Oreopithecus Oreopithecus bambolii Nakalipithecus † Nakalipithecus nakayamai Anoiapithecus † Anoiapithecus brevirostris Dryopithecus † Dryopithecus wuduensis Dryopithecus fontani Hispanopithecus † Hispanopithecus laietanus Hispanopithecus crusafonti Neopithecus † Neopithecus brancoi Pierolapithecus† Pierolapithecus catalaunicus Rudapithecus† Rudapithecus hungaricus Samburupithecus† Samburupithecus kiptalami Tribe Gorillini Chororapithecus † Chororapithecus abyssinicus Genus Gorilla Western gorilla, Gorilla gorilla Western lowland gorilla, Gorilla gorilla gorilla Cross River gorilla, Gorilla gorilla diehli Eastern gorilla, Gorilla beringei Mountain gorilla, Gorilla beringei beringei Eastern lowland gorilla, Gorilla beringei graueri Tribe Hominini Sahelanthropus† Sahelanthropus tchadensis Orrorin† Orrorin tugenensis Subtribe Panina Genus Pan Chimpanzee, Pan troglodytes Central chimpanzee, Pan troglodytes troglodytes Western chimpanzee, Pan troglodytes verus Nigeria-Cameroon chimpanzee, Pan troglodytes ellioti Eastern chimpanzee, Pan troglodytes schweinfurthii Bonobo, Pan paniscus Subtribe Hominina Graecopithecus † Graecopithecus freybergi.
Note: Graecopithecus has been subsumed by other authors into Dryopithecus. The placement of Graecopithecus within the Hominina, as shown here, represents a hypothesis, but not scientific consensus. Ardipithecus† Ardipithecus ramidus Ardipithecus kadabba Kenyanthropus† Kenyanthropus platyops Praeanthropus†Praeanthropus bahrelghazali Praeanthropus anamensis Praeanthropus afarensis Australopithecus† Australopithecus africanus Australopithecus garhi Australopithecus sediba Paranthropus† Paranthropus aethiopicus Paranthropus robustus Paranthropus boisei Homo – immediate ancestors of modern humans Homo gautengensis† Homo rudolfensis† Homo habilis† Homo floresiensis† Homo erectus† Homo ergaster† Homo antecessor† Homo heidelbergensis† Homo cepranensis† Denisovans † Homo neanderthalensis† Homo rhodesiensis† Homo sapiens Anatomically modern human, Homo sapiens sapiens Homo sapiens idaltu† Archaic Homo sapiens † Red Deer Cave people† The age of the subfamily Homininae is estimated at some 14 to 12.5 million years.
Its separation into Gorillini and Hominini is estimated to have occurred at about 8 to 10 million years ago during the late Miocene, close to the age of Nakalipithecus nakayamai. There is evidence there was interbreeding of Gorillas and the Pan-Homo ancestors until right up to the Pan-Homo split. Recent studies of Ardipithecus ramidus and Orrorin tugenensis suggest some degree of bipedalism. Australopit
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
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
The Paleolithic or Palaeolithic is a period in human prehistory distinguished by the original development of stone tools that covers c. 99% of human technological prehistory. It extends from the earliest known use of stone tools by hominins c. 3.3 million years ago, to the end of the Pleistocene c. 11,650 cal BP. The Paleolithic is followed in Europe by the Mesolithic, although the date of the transition varies geographically by several thousand years. During the Paleolithic, hominins grouped together in small societies such as bands, subsisted by gathering plants and fishing, hunting or scavenging wild animals; the Paleolithic is characterized by the use of knapped stone tools, although at the time humans used wood and bone tools. Other organic commodities were adapted for use including leather and vegetable fibers. About 50,000 years ago, there was a marked increase in the diversity of artifacts. In Africa, bone artifacts and the first art appear in the archaeological record; the first evidence of human fishing is noted, from artifacts in places such as Blombos cave in South Africa.
Archaeologists classify artifacts of the last 50,000 years into many different categories, such as projectile points, engraving tools, knife blades, drilling and piercing tools. Humankind evolved from early members of the genus Homo—such as Homo habilis, who used simple stone tools—into anatomically modern humans as well as behaviorally modern humans by the Upper Paleolithic. During the end of the Paleolithic the Middle or Upper Paleolithic, humans began to produce the earliest works of art and began to engage in religious and spiritual behavior such as burial and ritual; the climate during the Paleolithic consisted of a set of glacial and interglacial periods in which the climate periodically fluctuated between warm and cool temperatures. Archaeological and genetic data suggest that the source populations of Paleolithic humans survived in sparsely wooded areas and dispersed through areas of high primary productivity while avoiding dense forest cover. By c. 50,000 – c. 40,000 BP, the first humans set foot in Australia.
By c. 45,000 BP, humans lived at 61°N latitude in Europe. By c. 30,000 BP, Japan was reached, by c. 27,000 BP humans were present in Siberia, above the Arctic Circle. At the end of the Upper Paleolithic, a group of humans crossed Beringia and expanded throughout the Americas; the term "Palaeolithic" was coined by archaeologist John Lubbock in 1865. It derives from Greek: παλαιός, palaios, "old"; the Paleolithic coincides exactly with the Pleistocene epoch of geologic time, which lasted from 2.6 million years ago to about 12,000 years ago. This epoch experienced important climatic changes that affected human societies. During the preceding Pliocene, continents had continued to drift from as far as 250 km from their present locations to positions only 70 km from their current location. South America became linked to North America through the Isthmus of Panama, bringing a nearly complete end to South America's distinctive marsupial fauna; the formation of the isthmus had major consequences on global temperatures, because warm equatorial ocean currents were cut off, the cold Arctic and Antarctic waters lowered temperatures in the now-isolated Atlantic Ocean.
Most of Central America formed during the Pliocene to connect the continents of North and South America, allowing fauna from these continents to leave their native habitats and colonize new areas. Africa's collision with Asia created the Mediterranean, cutting off the remnants of the Tethys Ocean. During the Pleistocene, the modern continents were at their present positions. Climates during the Pliocene became cooler and drier, seasonal, similar to modern climates. Ice sheets grew on Antarctica; the formation of an Arctic ice cap around 3 million years ago is signaled by an abrupt shift in oxygen isotope ratios and ice-rafted cobbles in the North Atlantic and North Pacific Ocean beds. Mid-latitude glaciation began before the end of the epoch; the global cooling that occurred during the Pliocene may have spurred on the disappearance of forests and the spread of grasslands and savannas. The Pleistocene climate was characterized by repeated glacial cycles during which continental glaciers pushed to the 40th parallel in some places.
Four major glacial events have been identified, as well as many minor intervening events. A major event is a general glacial excursion, termed a "glacial". Glacials are separated by "interglacials". During a glacial, the glacier experiences minor retreats; the minor excursion is a "stadial". Each glacial advance tied up huge volumes of water in continental ice sheets 1,500–3,000 m deep, resulting in temporary sea level drops of 100 m or more over the entire surface of the Earth. During interglacial times, such as at present, drowned coastlines were common, mitigated by isostatic or other emergent motion of some regions; the effects of glaciation were global. Antarctica was ice-bound throughout the preceding Pliocene; the Andes were covered in the south by the Patagonian ice cap. There were glaciers in New Tasmania; the now decaying glaciers of Mount Kenya, Mount Kilimanjaro, the Ruwenzori Range in east and central Africa were larger. Glaciers existed to the west in the Atlas mountains. In the northern hemisphere, many glaciers fused into one.
Homo is the genus which emerged in the otherwise extinct Australopithecus genus that encompasses the extant species Homo sapiens, plus several extinct species classified as either ancestral to or related to modern humans, most notably Homo erectus and Homo neanderthalensis. The genus is taken to emerge with the appearance of Homo habilis, just over two million years ago. Genus Homo, together with the genus Paranthropus is sister to A. africanus in the genus Australopithecus, which itself had split from the lineage of Pan, the chimpanzees. Homo erectus appeared about two million years ago and, in several early migrations, it spread throughout Africa and Eurasia, it was the first human species to live in a hunter-gatherer society and to control fire. An adaptive and successful species, Homo erectus persisted for more than a million years, diverged into new species by around 500,000 years ago. Homo sapiens emerges close to 300,000 to 200,000 years ago, most in Africa, Homo neanderthalensis emerged at around the same time in Europe and Western Asia.
H. sapiens dispersed from Africa in several waves, from as early as 250,000 years ago, by 130,000 years ago, the so-called Southern Dispersal beginning about 70,000 years ago leading to the lasting colonisation of Eurasia and Oceania by 50,000 years ago. Both in Africa and Eurasia, H. sapiens interbred with archaic humans. Separate archaic human species are thought to have survived until around 40,000 years ago, with possible late survival of hybrid species as late as 12,000 years ago. See Homininae for an overview of taxonomy; the Latin noun homō means "human being" or "man" in the generic sense of "human being, mankind". The binomial name Homo sapiens was coined by Carl Linnaeus. Names for other species of the genus were introduced beginning in the second half of the 19th century. Today, the genus Homo has not been properly defined. Since the early human fossil record began to emerge from the earth, the boundaries and definitions of the genus Homo have been poorly defined and in flux; because there was no reason to think it would have any additional members, Carl Linnaeus did not bother to define Homo when he first created it for humans in the 18th century.
The discovery of Neanderthal brought the first addition. The genus Homo was given its taxonomic name to suggest that its member species can be classified as human. And, over the decades of the 20th century, fossil finds of pre-human and early human species from late Miocene and early Pliocene times produced a rich mix for debating classifications. There is continuing debate on delineating Homo from Australopithecus—or, delineating Homo from Pan, as one body of scientists argue that the two species of chimpanzee should be classed with genus Homo rather than Pan. So, classifying the fossils of Homo coincides with evidence of: 1) competent human bipedalism in Homo habilis inherited from the earlier Australopithecus of more than four million years ago, as demonstrated by the Laetoli footprints. From the late-19th to mid-20th centuries, a number of new taxonomic names including new generic names were proposed for early human fossils. Many such names are now dubbed as "synonyms" with Homo, including Pithecanthropus,Protanthropus,Sinanthropus,Cyphanthropus,Africanthropus,Telanthropus,Atlanthropus, Tchadanthropus.
Classifying the genus Homo into species and subspecies is subject to incomplete information and remains poorly done. This has led to using common names in scientific papers to avoid trinomial names or the ambiguity of classifying groups as incertae sedis —for example, H. neanderthalensis vs. H. sapiens neanderthalensis, or H. georgicus vs. H. erectus georgicus. Some extinct species in the genus Homo are only discovered and do not as yet have consensus binomial names. Since the beginning of the Holocene, it is that Homo sapiens has been the only extant species of Homo. John Edward Gray was an early advocate of classifying taxa by designating families. Wood and Richmond proposed that Hominini be designated as a tribe that comprised all species of early humans and pre-humans ancestral to humans back to after the chimpanzee-human last common ancestor. Designations alternative to Hominina existed, or were offered: Australopithecinae and Preanthropinae. See Hominini and Chimpanzee–human last common ancestor for the separation of Australopithecina and Panina.
Several species, including Australopithecus garhi, Australopithecus sediba, Australopithecus africanus, Australopithecus afarensis, have been proposed as the direct ancestor of the Homo lineage. These species have morphological features that align them with Homo
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 Cambrian Period was the first geological period of the Paleozoic Era, of the Phanerozoic Eon. The Cambrian lasted 55.6 million years from the end of the preceding Ediacaran Period 541 million years ago to the beginning of the Ordovician Period 485.4 mya. Its subdivisions, its base, are somewhat in flux; the period was established by Adam Sedgwick, who named it after Cambria, the Latin name of Wales, where Britain's Cambrian rocks are best exposed. The Cambrian is unique in its unusually high proportion of lagerstätte sedimentary deposits, sites of exceptional preservation where "soft" parts of organisms are preserved as well as their more resistant shells; as a result, our understanding of the Cambrian biology surpasses that of some periods. The Cambrian marked a profound change in life on Earth. Complex, multicellular organisms became more common in the millions of years preceding the Cambrian, but it was not until this period that mineralized—hence fossilized—organisms became common; the rapid diversification of life forms in the Cambrian, known as the Cambrian explosion, produced the first representatives of all modern animal phyla.
Phylogenetic analysis has supported the view that during the Cambrian radiation, metazoa evolved monophyletically from a single common ancestor: flagellated colonial protists similar to modern choanoflagellates. Although diverse life forms prospered in the oceans, the land is thought to have been comparatively barren—with nothing more complex than a microbial soil crust and a few molluscs that emerged to browse on the microbial biofilm. Most of the continents were dry and rocky due to a lack of vegetation. Shallow seas flanked the margins of several continents created during the breakup of the supercontinent Pannotia; the seas were warm, polar ice was absent for much of the period. Despite the long recognition of its distinction from younger Ordovician rocks and older Precambrian rocks, it was not until 1994 that the Cambrian system/period was internationally ratified; the base of the Cambrian lies atop a complex assemblage of trace fossils known as the Treptichnus pedum assemblage. The use of Treptichnus pedum, a reference ichnofossil to mark the lower boundary of the Cambrian, is difficult since the occurrence of similar trace fossils belonging to the Treptichnids group are found well below the T. pedum in Namibia and Newfoundland, in the western USA.
The stratigraphic range of T. pedum overlaps the range of the Ediacaran fossils in Namibia, in Spain. The Cambrian Period was followed by the Ordovician Period; the Cambrian is divided into ten ages. Only three series and six stages are named and have a GSSP; because the international stratigraphic subdivision is not yet complete, many local subdivisions are still used. In some of these subdivisions the Cambrian is divided into three series with locally differing names – the Early Cambrian, Middle Cambrian and Furongian. Rocks of these epochs are referred to as belonging to Upper Cambrian. Trilobite zones allow biostratigraphic correlation in the Cambrian; each of the local series is divided into several stages. The Cambrian is divided into several regional faunal stages of which the Russian-Kazakhian system is most used in international parlance: *Most Russian paleontologists define the lower boundary of the Cambrian at the base of the Tommotian Stage, characterized by diversification and global distribution of organisms with mineral skeletons and the appearance of the first Archaeocyath bioherms.
The International Commission on Stratigraphy list the Cambrian period as beginning at 541 million years ago and ending at 485.4 million years ago. The lower boundary of the Cambrian was held to represent the first appearance of complex life, represented by trilobites; the recognition of small shelly fossils before the first trilobites, Ediacara biota earlier, led to calls for a more defined base to the Cambrian period. After decades of careful consideration, a continuous sedimentary sequence at Fortune Head, Newfoundland was settled upon as a formal base of the Cambrian period, to be correlated worldwide by the earliest appearance of Treptichnus pedum. Discovery of this fossil a few metres below the GSSP led to the refinement of this statement, it is the T. pedum ichnofossil assemblage, now formally used to correlate the base of the Cambrian. This formal designation allowed radiometric dates to be obtained from samples across the globe that corresponded to the base of the Cambrian. Early dates of 570 million years ago gained favour, though the methods used to obtain this number are now considered to be unsuitable and inaccurate.
A more precise date using modern radiometric dating yield a date of 541 ± 0.3 million years ago. The ash horizon in Oman from which this date was recovered corresponds to a marked fall in the abundance of carbon-13 that correlates to equivalent excursions elsewhere in the world, to the disappearance of distinctive Ediacaran fossils. There are arguments that the dated horizon in Oman does not correspond to the Ediacaran-Cambrian boundary, but represents a facies change from marine to evaporite-dominated strata — which w