The horse evolution , a mammal of the Equidae family, occurred over a geological time scale of 50 million years, transforming small, sized dogs, dwelling forests into modern horses. Paleozoologists have been able to outline the evolution of a modern horse's evolutionary line that is more complete than any other animal. Much of this evolution takes place in North America, where horses originate but became extinct about 10,000 years ago.
The horse belongs to the Perissodactyla sequence (odd otters ungulates), members who share hooved legs and odd number of toes on each leg, as well as the upper lip of the same cell phone and tooth structure. This means the horse has the same ancestor as tapir and rhinoceros. Perissodactyls appear at the end of Paleocene, less than 10 million years after the Cretaceous-Paleogene extinction event. This group of animals seems originally specific to life in tropical forests, but while tapirs and, to some extent, rhinos, retain their forest specialties, modern horses are adapted to life on more dry land, in climatic conditions much harder than steppes. Other species of Equus are adapted to various medium conditions.
The earliest ancestors of modern horses walked on several diffused toes, an accommodation for living spent walking on moist and gentle soil in ancient woods. As grass species begin to emerge and develop, dietary equids shift from the leaves to the grass, leading to larger and more durable teeth. At the same time, when the steppe begins to emerge, the horse's predecessors must be able to speed higher to run faster than predators. This is achieved by extending the limbs and lifting several toes off the ground in such a way that the body weight is gradually placed on one of the longest toes, the third.
Video Evolution of the horse
History of research
Wild horses are known from prehistory from Central Asia to Europe, with domestic horses and other equids distributed more widely in the Old World, but no horses or equids of any kind are found in the New World when European explorers reach America. When the Spanish colony brought a domestic horse from Europe, beginning in 1493, the horse that fled quickly formed a large wild herd. In the 1760s, early naturalist buffons suggested this was an indication of the low self-esteem of the New World's fauna, but then reconsidered this idea. William Clark's 1807 expedition to Big Bone Lick found the "leg bones and legs of the Horses", which were included with other fossils sent to Thomas Jefferson and evaluated by the anatomist Caspar Wistar, but did not comment on the significance of these findings.
First Old World Ecological Fossils were discovered in the gypsum mine in Montmartre, Paris, in the 1820s. The tooth was sent to the Paris Conservatory, where it was identified by Georges Cuvier, who identified it as a horse-related tapir. Sketches of all the animals fit the skeletons later found on the site.
During the Beagle survey expedition, young naturalist Charles Darwin had a tremendous success with fossil hunting in Patagonia. On October 10, 1833, in Santa Fe, Argentina, he was "astonished" when he found a horse's teeth in the same layer as a fossilized giant armadillo, and wondered whether it might have been cleared from the later layers, but concluded it was "impossible ". After the expedition back in 1836, the anatomist Richard Owen confirmed that the tooth was from an extinct species, which he later named Equus Curvidens, and commented, "This is evidence of the existence of a genus, which , in connection with South America, has become extinct, and for the second time introduced to the Continent, is not one of the most unattractive fruits of the discovery of Mr. Darwin's ontological palate. "
In 1848, a study of American horse fossils by Joseph Leidy systematically examined the Pleistocene horse fossils from various collections, including from the Academy of Natural Sciences, and concluded at least two ancient horse species had been there. North America: Equus Curvidens and others, which he named Equus americanus . A decade later, he found out the last name had been taken and renamed it Equus complicatus . That same year, he visited Europe and was introduced by Owen to Darwin.
The original sequence of species believed to have evolved into horses was based on fossils found in North America in the 1870s by Othniel pamphletologist Charles Marsh. The sequence, from Eohippus to modern horse (Equus ), was popularized by Thomas Huxley and became one of the most obvious examples of evolutionary evolution. The pedigree of horse evolution became a common feature of biological textbooks, and a series of transitional fossils assembled by the American Museum of Natural History became an exhibition that emphasized the gradual evolution of the "horizontal line" of horses.
Since then, as the number of equid fossils has increased, the actual evolutionary development of Ebiippus to Equus has been found to be much more complex and multibranched than originally thought. Straight, the direct development from the previous to the last has been replaced by a more elaborate model with many branches in different directions, where the modern horse is only one of many. George Gaylord Simpson in 1951 first admitted that modern horses are not the "purpose" of the whole lineage, but are the only genus of many surviving horse lines.
Detailed fossilized information about the distribution and rate of change of new bird species also reveals that inter-species developments are not as smooth and consistent as they once believed. Although some transitions, such as Dinohippus to Equus , are indeed gradual developments, a number of others, such as Epihippus to Mesohippus , relatively sudden in geological time, which occurs only a few million years. Both anagenesis (gradual change in the frequency of the whole population gene) and cladogenesis (populations "divide" into two distinct branches of evolution) occur, and many species coexist with "ancestral" species at various times. The change in the nature of equids is also not always the "straight line" of Ebiippus to Equus: several self-reversed features at various points in the evolution of new equid species, such as the size and presence of the face fossae , and only in retrospect can certain evolutionary trends be recognized.
Maps Evolution of the horse
Before weird faceless ungulates
Phenacodontidae
Phenacodontidae is the latest family in the order of Condylarthra which is believed to be the ancestor of the odd ungulates. It contains the genera of Almogaver , Copecion , Ectocion , Eodesmatodon , Meniscotherium , Ordathspidotherium , Phenacodus and Pleuraspidotherium . The family lived from the Early Paleocene to the Middle Eocene in Europe and the size of a sheep, with a tail that was slightly less than half their body length and unlike their ancestors, a good running skill to avoid predators.
Eocene and Oligocene: early equids
Eohippus
Eohippus appeared in Ypresian (early Eocene), about 52 mya (millions of years ago). A fox-sized animal (250-450 mm), with a relatively short head and neck and a curved and curved back. It has 44 crowned lower teeth, in a typical arrangement of omnivorous cruise mammals: three incisors, a canine tooth, four premolar teeth, and three molars on each side of the jaw. The molars are uneven, dull, and wavy, and are used primarily to grind the leaves. The cusp of the molar is slightly connected at the low peak. Eohippus explores the soft foliage and fruit, possibly running among the bushes in modern muntjac mode. It has a small brain, and has a small frontal lobe.
His limbs are relatively long on his body, already showing the beginning of adaptation to run. However, all the main leg bones are not used, leaving the legs flexible and rotatable. His wrists and hands were low to the ground. Forelimbs have developed five toes, four of which are equipped with small proto-nails; the fifth great "toe-thumb" was released from the ground. The hind legs have small toenails on three of the five toes, while the first and fifth vestigial fingers do not touch the ground. Her legs are cushioned, like dogs, but with tiny nails in the claws.
Over a span of about 20 million years, Eohippus developed with some significant evolutionary changes. The most significant changes occur in the teeth, which begin to adapt to the changing diet, as this early Equidae shifts from the fruity and fruity mixed diet to the main focus of the food exploring. During the Eocene, the Eohippus species (most likely Eohippus angustidens) branches into various new types of Equidae. Thousands of complete skeletons of fossils from these animals have been found in the Eocene layer of North America, especially in the valley of the Wind River in Wyoming. Similar fossils have also been found in Europe, such as Propalaeotherium (which is not considered a modern horse ancestor). Orohippus
About 50 million years ago, in early-to-middle Eocene, Ebiippus was smoothly diverted to Orohippus through a series of gradual changes. Although its name means "mountain horse", Orohippus is not a true horse and does not live on the mountain. It resembles Eohippus in size, but has a slimmer body, elongated head, slender forelimbs, and longer hind legs, all of which are characteristics of a good jumper. Although Orohippus is still footed, the vestigial outer edge of Eohippus is not present at Orohippus ; there are four fingers on each front foot, and three on each hind leg.
The most dramatic changes between Ezippus and Orohippus are in the teeth: the first premolars are dwarfed, the last premolar shifts in shape and serves to molar, and the emblems of teeth become more pronounced. Both of these factors provide greater Orohippus grinding ability, indicating Orohippus consuming harder plant material.
Epihippus
In the middle of the Eocene, about 47 million years ago, Epihippus, the genus that continued the evolving trend of milling gears evolved from Orohippus. Epihippus has five cheek teeth that rub against and low crown with well-formed tops. The late species of Epihippus , sometimes referred to as Duchesnehippus intermedius , have teeth similar to the Oligocene equoid, although slightly underdeveloped. Whether Duchesnehippus is a subgenus of Epihippus or a different genus is debated. Epihippus is only 2 meters away.
Mesohippus
At the end of the Eocene and early stages of the Oligocene period (32-24 mya), the North American climate becomes drier, and the earliest grass begins to evolve. The forests produce flat plains, houses for grasses and various types of brushes. In some areas, these plains are covered in sand, creating a type of environment that resembles grasslands today.
In response to a changing environment, the now alive Equidae species are also beginning to change. At the end of the Eocene, they begin to develop tougher teeth and become slightly larger and lighter, allowing for faster walking speeds in open areas, and thus to avoid predators in non-timber areas. Around 40 mya, Mesohippus ("middle horse") suddenly developed in response to a strong new selective pressure to adapt, starting with the Mesohippus celer species and soon to be followed by < i> Mesohippus westoni .
At the beginning of the Oligocene, Mesohippus is one of the broadest mammals in North America. It runs with three toes on each front and back of the foot (the first and fifth toes remain, but small and not used in walking). The third toe is stronger than the outside, and thus more weighty; the fourth toe is released to the vestigial headstone. Judging from the longer, leaner limbs, Mesohippus is a vivacious animal.
Mesohippus is slightly larger than Epihippus , about 610 mm (24 inches) across the shoulder. His back was less curved, and his face, muzzle, and neck were rather long. It has a much larger cerebral hemisphere, and has a small shallow depression on its skull called fossa, which in modern horse is quite detailed. Fossa serves as a useful marker for identifying fossil species of horses. Mesohippus has six "cheek teeth" that grind, with one premolar up front - a feature that all of Equidae's descendants will defend. Mesohippus also has the sharp teeth of Epihippus , enhancing its ability to grind perennials.
Miohippus
About 36 million years ago, soon after the development of Mesohippus Miohippus (the "little horse") appeared, the earliest species was Miohippus assiniboiensis . As with Mesohippus, the appearance of Miohippus was relatively abrupt, although some transitional fossils linking the two genera have been found. Mesohippus was previously believed to have evolved anogenically into Miohippus by a series of gradual progression, but new evidence has shown its evolution is cogogenetic: a Miohippus population split from the genus main Mesohippus , coexisted with Mesohippus for about four million years, and then over time came to replace Mesohippus.
Miohippus is significantly larger than its predecessor, and the ankle joints change subtly. Fossa's face is larger and deeper, and also begins to show extra variable spikes on his upper cheek teeth, a trait that characterizes horse teeth.
Miohippus usher in a new diversification period at Equidae. While Mesohippus died in mid-Oligocene, Miohippus continued to grow, and at the beginning of Miocene (24-5.3 mya), it began to rapidly diversify and speciation. It branches into two large groups, one of which is adapted to life in the forest once again, while others remain suitable for living in grasslands.
Miosen and Pliosen: true equines
Kalobatippus
The suitable form for forests is Kalobatippus (or Miohippus intermedius , depending on whether it is a genus or a new species), whose second and fourth index fingers are long, perfectly suited for journeys on the forest floor that is soft. Kalobatippus might bring up Anchitherium , who traveled to Asia via the Bering Strait overland bridge, and from there to Europe. Both in North America and Eurasia, the larger genera evolved from Anchitherium : Sinohippus in Eurasia and Hypohippus and Megahippus in North America. Hypohippus is extinct by the Late Miocene.
Parahippus
The remaining Miohippus population of the steppe is believed to be the ancestor of Parahippus, a North American animal the size of a small pony, with a prolonged skull and facial structure. resembles a horse today. The three legs are stronger and bigger, and carry the main body load. The four premolars resemble molars; the first small and almost non-existent. The incisors, like their predecessor teeth, have a crown (like human incisors); however, the upper incisors have a shallow crease mark that marks the beginning of the core/cup.
Merychippus
In the midst of the Miocene, grazer Merychippus developed. It has a wider molars than its predecessor, which is believed to have been used to chew steppe hard grass. The hind legs, which are relatively short, have toes equipped with tiny nails, but they may only touch the ground when running. Merychippus emits to at least 19 additional grassland species.
Hipparion
The three lineages in Equidae are believed to come from various varieties of Merychippus : Hipparion , Protohippus and Pliohippus . The most distinct of Merychippus is Hipparion , especially in tooth enamel structure: compared to the other Equidae, the inside, or the side of the tongue, has a fully isolated barrier wall. A complete and well-preserved framework from North America Hipparion shows an animal the size of a small pony. They are very slender, somewhat antelope-like, and adapt to life in dry grassland. On its slender legs, Hipparion has three toes fitted with tiny nails, but the toes do not touch the ground.
In North America, Hipparion and its relatives ( Cormohipparion , Nannippus , Neohipparion , and Pseudhipparion ), mushrooming into various types of equids, at least one that successfully migrated to Asia and Europe during the Miocene epoch. (Europe Hipparion is different from America Hipparion in its smaller body size - the most famous invention of these fossils is near Athens.)
Pliohippus
Pliohippus appears from Callippus in the middle Miocene, about 12 mya. It's very similar in appearance to Equus , although it has two extra long toes on either side of the nail, externally barely visible as a splattering bulge. Long and slender limbs from Pliohippus reveal fast-foot steppes.
Until now, Pliohippus is believed to be the ancestor of today's horses because of many anatomical similarities. However, although Pliohippus is clearly a close relative of Equus , its skull has a deep facial fossa, whereas Equus has no fos at all. In addition, his teeth are very curved, unlike a very modern straight horse's teeth. Consequently, it is impossible to be the ancestor of a modern horse; on the contrary, it is a possible candidate for the ancestors of Astrohippus .
Dinohippus
Dinohippus is the most common Equidae species in North America during the end of Pliocene. Initially considered monodactyl, but the 1981 fossil findings in Nebraska show some tridactyl.
Plesippus
Plesippus is often considered a transitional stage between Dinohippus and an extant genus, Equus .
The famous fossils discovered near Hagerman, Idaho were originally thought of as part of the genus Plesippus . Hagerman Fossil Beds (Idaho) is a Pliocene site, measuring about 3.5 mya. The fossil remains were originally called Plesippus shoshonensis , but further studies by paleontologists determined that fossils represented the oldest remains of the genus equus . Their estimated average weight is 425 kg, about the size of an Arabian horse.
At the end of Pliocene, the climate in North America began to cool significantly and most animals were forced to move south. One population of Plesippus moved across the Bering land bridge to Eurasia about 2.5 mya.
Modern horse
Equus
The Equus genus, which includes all remaining horses, is believed to have evolved from Dinohippus , through the middle form Plesippus . One of the oldest species is Equus simplicidens , described as zebra-like with donkey-shaped heads. The oldest fossil to date ~ 3.5 million years from Idaho, USA. The genus appears to have spread rapidly into the Old World, with the same age Equus livenzovensis documented from Western Europe and Russia.
The phylogeny molecule shows the newest ancestors of all modern equids (members of the genus Equus ) live ~ 5.6 (3.9-7.8) mya. The direct paleogenomic sequence of the Pleasanterian 700-year-old middle-aged Pleistocene bone from Canada implies more recent Myr 4.04 before the present date for the latest common ancestor (MRCA) in the 4.0-4.5 Myr BP range. The oldest distinctions are the Asian hemion (subgenus E. (Asinus), including the moon, onager, and kiang), followed by the African zebra (subgenera E (Dolichohippus) i> E. (Hippotigris) ). All other modern forms include the pet horse (and many forms of the Pliocene and Pleistocene fossils) belonging to a subgenus E. (Equus) that deviated ~ 4.8 (3.2-6.5) million years ago.
Pleistocene horse fossils have been established for many species, with over 50 species of horses described from the Pleistocene of North America alone, although the taxonomic validity of most of these has been questioned. Recent genetic work on fossils has found evidence for only three genetically different lineages in the Northern Pleistocene and South America. These results show that all North American caballine horse fossils (which also include European and Asian Przewalski pets and horses), and South American fossils traditionally placed in the subgenus of E. (Amerhippus) belonging to the same species : E. ferus . It remains associated with various species and incorporated as a New World legged horse (including E. Francisci , E. Tau , E. Quinni and potentially fossil Pleistocene North America was previously associated with E. cf. hemiones , and E. (Asinus) ciang kiang ) may belong to both endemic species to America The north, which although superficially similar to the species in the subgenus E. (Asinus) (and hence sometimes referred to as North American butt) is closely related to E. ferus . Surprisingly, the third species, endemic to South America and traditionally referred to as Hippidion , originally believed to be descended from Pliohippus , proved to be the third species in the genus Equus , closely linked to the New World legged horse. The temporal and regional variations in body size and morphological features in each lineage show remarkable intraspecific plasticity. Such environmental-driven adaptation changes will explain why the taxonomic diversity of the Pleistocene equis has been exaggerated on a morphoanatomical basis.
According to this result, the genus Equus evolved from the ancestor <~> Dinohippus ~ like mya ~ 4-7. It quickly spread to the Old World and there diversified into mule and zebra species. The North American lineage of the subgenus E. (Equus) evolved into a New World Legged Horse (NWSLH). Furthermore, the populations of these species entered South America as part of the Great American Interchange shortly after the formation of the Isthmus of Panama, and evolved into a form currently called the Hippidion 2.5 million years ago. Hippidion is only remotely related to morphologically similar to Pliohippus , which may become extinct during the Miocene. Both NWSLH and Hippidium show adaptation to dry, barren soil, whereas short legs Genome sequencing
In June 2013, a group of researchers announced that they had sequenced DNA of horses aged 560-780 thousand years, using material taken from leg bones found buried in permafrost in the Yukon region of Canada. Prior to this publication, the oldest nuclear genome that had been successfully sorted was 110-130 thousand years ago. In comparison, the researchers also sequenced the genome of the 43,000-year-old Pleistocene horses, the Przewalski horses, the five modern horse races, and donkeys. Analysis of the differences between these genomes shows that the last ancestors of modern horses, donkeys, and zebras aged 4 to 4.5 million years ago. The results also show that the Przewalski horse deviated from other modern horse types some 43,000 years ago, and never in its evolutionary history has been tamed.
Pleistocene extinction
Excavations in western Canada have found evidence of horse in North America up to about 12,000 years ago. However, all Equidae in North America are finally extinct. The cause of this extinction (along with the extinction of various other American megafauna) has been the subject of much debate. Given the sudden events and because these mammals have grown rapidly over the past millions of years, something very unusual must have happened. The first major hypothesis linking extinctions to climate change. For example, in Alaska, starting about 12,500 years ago, the grasses that characterize the steppes ecosystem provide a way for the tundra bush, which is covered with an unpleasant plant. Another hypothesis showing extinction is associated with overexploitation by newly arrived humans from naïve prey who are not habituated by their hunting methods. Extinction almost simultaneously with the end of the latest glacial advances and the rise of Clovis hunting-game culture. Some research suggests humans may arrive in Alaska at the same time or shortly before the local extinction of the horse. In addition, it has been proposed that the transition of stepa-tundra vegetation in Beringia may have been a consequence, not the cause, of the extinction of megafaunal grazers.
In Eurasia, fossil horses began to appear frequently on archaeological sites in Kazakhstan and southern Ukraine about 6,000 years ago. Since then, the pets, as well as the knowledge of capturing, taming, and rearing horses, may spread relatively quickly, with wild horses from some of the wild populations included in the journey.
Return to America
The horse only returned to America with Christopher Columbus in 1493. It was the first Iberian horse to be brought to Hispaniola and then to Panama, Mexico, Brazil, Peru, Argentina, and, in 1538, Florida. The first horse to return to the main continent was a specially identified 16 horses carried by HernÃÆ'¡n CortÃÆ'Â © s. The next explorers, such as Coronado and De Soto, carry a growing number, some from Spain and others from breeding grounds set up by Spaniards in the Caribbean. Later, when the Spanish mission was established on land, the horses would eventually be lost or stolen, and mushroomed into large herds of wild horses known as mustangs.
The indigenous peoples of America have no special word for horses, and come to refer them in various languages ​​as dog or deer types (in one case, "dog-deer", in other cases "big dog" or "seven dogs", referring to the weight each animal can be drawn).
Details
Fingers
The horse's ancestors came to walk only on the toes of the third and second toes. Skeletal remains indicate clear wear on the back of both sides of metacarpal and metatarsal bones, commonly called "splints". They are the rest of the second and fourth toes. Modern horses maintain the splint; they are often believed to be a useless attachment, but they actually play an important role in supporting carpal joints (front knees) and even tarsal joints (hocks).
Dental
Throughout the development of phylogenetics, horse teeth changed significantly. Types of native omnivorous teeth with short, "wavy" short teeth, with which the main members of the evolutionary line differentiate themselves, gradually transform into common teeth for herbivorous mammals. They become long (as much as 100 mm), about a molar of cubes equipped with a flat milling surface. In relation to the teeth, during the evolution of the horse, the elongation of the skull's face is apparent, and can also be observed on the back end of the eye. In addition, the relatively short horseshoe's neck becomes longer, with the same leg lengthening. Finally, body size grows as well.
Coat color
The color of the ancestral coat of E. ferus is probably uniform, consistent with the modern population of Przewalski horses. Variations of pre-domestication including black and visible have been inferred from cave wall paintings and confirmed by genomic analysis. Domestication may also cause more color variations of the mantle.
See also
- Evidence of common ancestry
Further reading
- MacFadden, Bruce J (1994). Horse Fossils: Systematics, Paleobiology, and Family Evolution Equidae . Cambridge & amp; New York: Cambridge University Press. ISBN: 0-521-47708-5 . Retrieved June 6 2010 .
References
External links
- Horse Evolution Over 55 Million Years . Tufts University. January 10, 1998 . Retrieved July 11, 2007 . Ã, : A collection of excluded images from horse fossils
- Horse Evolution
Source of the article : Wikipedia
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