From the Horse's Mouth: Teeth Reveal Evolution
No evolution of any species is as well documented as that of the horse. The fossils are classified in dozens of genera and hundreds of species, as is shown in the figure . On the family tree above, the relationship is not accurately presented ;. The evolutionary lineage of the horse is among the best-documented in all Eohippus was, in fact, so unhorselike that its evolutionary relationship to the. But what is it that makes humans and horses so perfect for each other? and back in time to the mysterious beginnings of the horse-human relationship. Meet The Horse: The Tiny Tropical Creature That Evolved Into Our.
Mesohippus was once believed to have anagenetically evolved into Miohippus by a gradual series of progressions, but new evidence has shown its evolution was cladogenetic: Its facial fossa was larger and deeper, and it also began to show a variable extra crest in its upper cheek teeth, a trait that became a characteristic feature of equine teeth. Miohippus ushered in a major new period of diversification in Equidae. Kalobatippus probably gave rise to Anchitheriumwhich travelled to Asia via the Bering Strait land bridgeand from there to Europe.
Its third toe was stronger and larger, and carried the main weight of the body. Its four premolars resembled the molar teeth; the first were small and almost nonexistent.
Merychippus[ edit ] Merychippusan effective grazer and runner In the middle of the Miocene epoch, the grazer Merychippus flourished.
It had wider molars than its predecessors, which are believed to have been used for crunching the hard grasses of the steppes. The hind legs, which were relatively short, had side toes equipped with small hooves, but they probably only touched the ground when running. Hipparion[ edit ] Protohippus simus Three lineages within Equidae are believed to be descended from the numerous varieties of Merychippus: HipparionProtohippus and Pliohippus.
The most different from Merychippus was Hipparion, mainly in the structure of tooth enamel: A complete and well-preserved skeleton of the North American Hipparion shows an animal the size of a small pony.
They were very slim, rather like antelopesand were adapted to life on dry prairies. On its slim legs, Hipparion had three toes equipped with small hooves, but the side toes did not touch the ground. In North America, Hipparion and its relatives CormohipparionNannippusNeohipparionand Pseudhipparionproliferated into many kinds of equidsat least one of which managed to migrate to Asia and Europe during the Miocene epoch.
Pliohippus[ edit ] Pliohippus pernix Pliohippus arose from Callippus in the middle Miocene, around 12 mya. It was very similar in appearance to Equusthough it had two long extra toes on both sides of the hoof, externally barely visible as callused stubs.
The long and slim limbs of Pliohippus reveal a quick-footed steppe animal. Until recently, Pliohippus was believed to be the ancestor of present-day horses because of its many anatomical similarities. However, though Pliohippus was clearly a close relative of Equus, its skull had deep facial fossae, whereas Equus had no fossae at all. Additionally, its teeth were strongly curved, unlike the very straight teeth of modern horses. Consequently, it is unlikely to be the ancestor of the modern horse; instead, it is a likely candidate for the ancestor of Astrohippus.
It was originally thought to be monodactyl, but a fossil find in Nebraska shows some were tridactyl. Mounted skeleton of Hagerman horse Equus simplicidens Plesippus is often considered an intermediate stage between Dinohippus and the extant genus, Equus.
Horse - Evolution of the horse | pdl-inc.info
The famous fossils found near Hagerman, Idaho were originally thought to be a part of the genus Plesippus. Hagerman Fossil Beds Idaho is a Pliocene site, dating to about 3. The fossilized remains were originally called Plesippus shoshonensis, but further study by paleontologists determined the fossils represented the oldest remains of the genus Equus.
At the end of the Pliocene, the climate in North America began to cool significantly and most of the animals were forced to move south. Equus—the genus to which all modern equines, including horses, assesand zebrasbelong—evolved from Pliohippus some 4 million to 4. Equus shows even greater development of the spring mechanism in the foot and exhibits straighter and longer cheek teeth. This new form was extremely successful and had spread from the plains of North America to South America and to all parts of the Old World by the early Pleistocene the Pleistocene Epoch lasted from about 2, to 11, years ago.
Equus flourished in its North American homeland throughout the Pleistocene but then, about 10, to 8, years ago, disappeared from North and South America. Scholars have offered various explanations for this disappearance, including the emergence of devastating diseases or the arrival of human populations which presumably hunted the horse for food.
Despite these speculations, the reasons for the demise of Equus in the New World remain uncertain. The submergence of the Bering land bridge prevented any return migration of horses from Asia, and Equus was not reintroduced into its native continent until the Spanish explorers brought horses in the early 16th century.
During the Pleistocene the evolution of Equus in the Old World gave rise to all the modern members of the genus. The modern horse, Equus caballus, became widespread from central Asia to most of Europe. Origin of horse domestication Archaeological evidence indicates that the domestication of horses had taken place by approximately 6, years ago in the steppe lands north of the Black Sea from Ukraine to Kazakhstan.
Despite intensive study over a long period of time, many questions remain about the early development of the species as it underwent domestication. One crucial question involves whether domestication was limited to a single location or occurred in multiple areas.
Tied to this question of origins is whether domesticated horses spread throughout Eurasia or whether the practice of horse domestication spread to new areas, with local breeders capturing their own wild horses and introducing them to the domestic horse gene pool. Results of studies of mitochondrial DNA mtDNAwhich is inherited only from the mother, showed a great deal of diversity among individuals and strongly supported the idea that wild horses from many different geographic areas contributed to the domestic horse.
The mtDNA data clearly indicated that there were multiple sites of domestication, with a large number of mares in the first populationsand that genetic input from local wild horses had been introduced into the domestic gene pool as domesticated horses spread.
In contrast, studies have revealed that the domestic horse is dominated by a single, paternally inherited Y chromosome lineage, in which there is almost no variation. An exception was a study of horses in southwestern China that found that some southern Chinese populations of male horses possessed a Y chromosome variant that was not present in any other breeds that had been tested.
This variant may represent a different paternal lineage that survived in the region, or it may represent a recent mutation. The lack of variation on the Y chromosome would seem to indicate a very narrow origin for the domestic horse. However, the differences in variation between maternal and paternal lineages may reflect the differences in how breeders treated mares and stallions. It is possible that throughout history far more mares contributed to the founding of the domestic horse than stallions, because stallions can be difficult to handle.
In addition, most selection is directed toward the males, because at the level of the individual they can produce such a large number of offspring compared with females. In other words, it is likely that a small number of relatively cooperative stallions may have been used to impregnate large numbers of mares. Studies examining other regions of DNA have revealed a high genetic diversity in horses, which is consistent with mtDNA results.
Research at the turn of the 21st century indicated that there appears to have been an independent domestication event in the Iberian Peninsula the region containing Spain and Portugalwhich served as a refuge for many speciesincluding horses, during the Pleistocene and Holocene glaciations.
In addition, evidence indicates that humans spread domestic horses from western Eurasia and that domestic populations were supplemented with wild individuals which increased the genetic diversity of domestic horses. Body size, leg length and skull length increased and the bones of the legs grew together.
These horses stood on the tips of their toes and hooves and therefore more upright. They were more suited to run on hard ground and the flexible leg rotation was limited. Merychippus Merychippus is an example.
It looked like a 'real' horse as we know it today and lived 17 to 10 million years ago. It was not only an effective grazer but also a fast runner thanks to its long legs. Its hind legs were shorter than those of its predecessors and it was larger shoulder height 1 meter and had a longer neck. It had wider molars with a higher crown and a hard layer of cement, which were used to grind the hard grasses of the steppe. It stood on one toe, the two smaller ones with little hooves were perhaps needed for support and probably only touched the ground while the horse was running.
The brains were larger and the eyes were further back. Like with Miohippus, three lines of species arose from Merychippus as a result of which horses had a maximum variety 10 million years ago: Three-toed horses, the Hipparion group, very varied in species, both browsers and grazers. Horses with a reduced number of toes, the "true equines".
Hipparion A complete preserved skeleton of a North American Hipparion shows an animal as large as a small pony, slender as a gazelle and adapted to life on dry prairies.
On the slender legs Hipparion had three toes with small hooves, the side toes did not touch the ground. Pliohippus Pliohippus lived from about 12 million years ago and looked like the modern horse Equus. Early species still had three toes, later ones had remains of the second - and fourth toes on the outside of the remaining toe, the splint bones. The long and slender legs made Pliohippus a fleet-footed steppe animal.
The neck was long and strong. The molars were strongly curved as opposed to the straight molars of Equus. For a long time Pliohippus was assumed to be the ancestor of Equus. That is not the case, although they are closely related. On the family tree above, the relationship is not accurately presented; Dinohippus fits better as the ancestor of Equus.
Dinohippus The more heavily build Dinohippus arose 12 million years ago. A succession of different species - gradually resembling Equus more and more - has been found. This growing resemblance applies to the molars, which became straight, the legs and the skull. Monodactyly evolved twice, once in Pliohippus and once in Dinohippus.
From the Horse's Mouth: Teeth Reveal Evolution
Equus The horses of the genus Equus first appeared about 3,5 million years ago. The oldest representative has been described as zebra-like, with the head of a donkey. Equus spread rapidly in the Old World.
There is a great variety of form in Equus, hence it was thought that in the Pleistocene many species existed in America. This is not the case. In the Quaternary only three species are recognized with a plastic, flexible power to adapt to the circumstances.
The physique resembles that of the current horses and donkeys. The legs were strong, so it could run fast. The length of the legs could be shorter or longer than that of the wild horses of present times.
Evolution of the horse - Wikipedia
After the ice age, years ago, the horse died out in America, along with some other big animals like the mammoth, the woolly rhinoceros and the ground sloth. This is explained by the warming of the climate, which brought grasses with a higher content of silica, as a result of which the molars wore off faster.
The animals grew less old and could get fewer offspring. Also, grass was replaced by less edible vegetation. Hunting may also have played a role. In the Old World horses, zebras and donkeys did not die out.
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Around years ago, people in Kazakhstan began riding horses for the first time. It seems to me that the explanations for extinction are debatable. The horses had already experienced several ice ages and warmings in the lastyears.
Moreover, the number of human inhabitants of North America was small at the time of the extinction; the first humans arrived only 12, years ago. Physical characteristics In the following some trends are discussed that are obvious during the evolution of the horse. Horses grow bigger in the course of time. Sometimes there are species that are much smaller. And over a long period of time, the size may stay the same, but then the molars may change, for example.
The evolution of the horse is not a straight line. As the family tree shows it is a richly branched shrub.X and Y Shiny Horsea Evolving Into Shiny Seadra!
Branches arise and become extinct millions of years later and it is not clear why one branch continues and another stops. Different species can co-exist for a long time, - cf. Browsers and grazers can co-exist peacefully, as they have a different environment. Appearance In the course of time, horses grew bigger. Unfortunately, the image of the modern horse in the drawing above is distorted, because it is a bred horse. But even the wild horse 1. During evolution, the horse got longer legs and a longer neck.