One of the best known and best studied of the paleontological evidence for evolution is the phylogenetic series of modern ungulates. Multiple paleontological finds and identified transitional forms create a scientific evidence base for this series. The phylogenetic series of the horse, described by the Russian biologist Vladimir Onufrievich Kovalevsky back in 1873, remains today an “icon” of evolutionary paleontology.
Evolution through the ages
In evolution, phylogenetic series are successive transitional forms that led to the formation of modern species. By the number of links, the series can be complete or partial, however, the presence of successive transitional forms is a prerequisite for their description.
The phylogenetic series of the horse is considered evidence of evolution precisely because of the presence of such successive forms,replacing each other. The multiplicity of paleontological finds endows it with a high degree of reliability.
Examples of phylogenetic series
The row of horses is not the only one among the examples described. The phylogenetic series of whales and birds is well studied and has a high degree of reliability. And controversial in scientific circles and most used in various populist insinuations is the phylogenetic series of modern chimpanzees and humans. Disputes about the intermediate links missing here do not subside in the scientific community. But no matter how many points of view, the importance of phylogenetic series as evidence of the evolutionary adaptability of organisms to changing environmental conditions remains indisputable.
Connecting the evolution of horses with the environment
Multiple studies of paleontologists have confirmed the theory of O. V. Kovalevsky about the close relationship of changes in the skeleton of the ancestors of horses with changes in the environment. The changing climate led to a decrease in forest areas, and the ancestors of modern single-toed ungulates adapted to living conditions in the steppes. The need for rapid movement provoked modifications in the structure and number of fingers on the limbs, changes in the skeleton and teeth.
First link in the chain
In the early Eocene, more than 65 million years ago, the first great ancestor of the modern horse lived. This is a “low horse” or Eohippus, which was the size of a dog (up to 30 cm), relied on the entire foot of the limb, on which there were four (front) and three (rear) fingers withlittle hooves. Eohippus fed on shoots and leaves and had tuberculate teeth. Brown coloration and sparse hair on a mobile tail - such is the distant ancestor of horses and zebras on Earth.
Intermediates
About 25 million years ago, the climate on the planet changed, and steppe expanses began to replace forests. In the Miocene (20 million years ago), mesogippus and parahippus appear, already more similar to modern horses. And the first herbivorous ancestor in the phylogenetic series of the horse is considered to be merikgippus and pliogippus, which enter the arena of life 2 million years ago. Hipparion - the last three-fingered link
This ancestor lived in the Miocene and Pliocene on the plains of North America, Asia and Africa. This three-toed horse, resembling a gazelle, did not yet have hooves, but could run fast, ate grass, and it was she who occupied vast territories.
One-toed horse - pliogippus
These one-toed representatives appear 5 million years ago in the same territories as the hipparions. Environmental conditions are changing - they are becoming even drier, and the steppes are growing significantly. This is where single-fingeredness turned out to be a more important sign for survival. These horses were up to 1.2 meters high at the withers, had 19 pairs of ribs and strong leg muscles. Their teeth acquire long crowns and folds of enamel with a developed cement layer.
The horse we know
The modern horse as the final stage of the phylogenetic series appeared at the end of the Neogene, and at the end of the last ice age (about 10 thousandyears ago) millions of wild horses were already grazed in Europe and Asia. Although the efforts of primitive hunters and the reduction of pastures made a wild horse a rarity already 4 thousand years ago. But two of its subspecies - the tarpan in Russia and the Przewalski's horse in Mongolia - managed to hold out much longer than all the others.
Wild horses
Today there are practically no real wild horses left. The Russian tarpan is considered an extinct species, and the Przewalski's horse does not occur naturally. Herds of horses that graze freely are feral domesticated forms. Such horses, though quickly returning to wild life, are still different from truly wild horses.
They have long manes and tails, and they are variegated. Exclusively tan horses of Przewalski and mouse tarpans have, as it were, trimmed bangs, manes and tails.
In Central and North America, wild horses were completely exterminated by the Indians and appeared there only after the arrival of Europeans in the 15th century. The feral descendants of the horses of the conquistadors gave rise to numerous herds of mustangs, the number of which is now controlled by shooting.
Besides mustangs, there are two types of wild island ponies in North America - on Assateague and Sable Islands. Semi-wild herds of Camargue horses are found in the south of France. In the mountains and swamps of Britain, you can also find some wild ponies.
Our favorite horses
Man tamed the horse and bred more than 300 of its breeds. From heavyweights to miniature ponies and handsome race breeds. About 50 breeds of horses are bred in Russia. The most famous of them is the Oryol trotter. Exceptionally white color, excellent lynx and agility - these qualities were so appreciated by Count Orlov, who is considered the founder of this breed.
