Equus (modern horse).
Equus is the only surviving genus in the once diverse family of horses.
The early Equus had zebra like bodies and short donkeys like heads. They had tails although short and stiff and straight up manes. Many of the strains of horses died off for reasons unknown aside from the obvious but Equus managed to survive and is where we find the basis for the modern day horse.
Species of Equus lived from 5 million years ago until the present. Living species include horses, asses, and zebras. Fossils of Equus are found on every continent except Australia and Antarctica.
Members of Equus still retain the genes for making side toes. Usually these express themselves only as the vestigial "splint bones" of toes 2 and 4, around the large central 3rd toe. Very rarely, a modern Equus is born with small but fully-formed side toes.
The earliest known Equus species were a set of three "simple Equus" species collectively known as the Equus simplicidens group. They still had some primitive traits from Dinohippus, including a slight facial fossa. They had zebra-like bodies (relatively stocky with a straight shoulder and thick neck), and short, narrow, donkey-like skulls. They probably had stiff, upright manes, ropy tails, medium-sized ears, striped legs, and at least some striping on the back (all traits shared by modern equines). They quickly diversified into at least 12 new species in 4 different groups, in a burst of evolution reminiscent of the great merychippine radiation. All these Equus species coexisted with other one-toed horses (such as Astrohippus) and with various successful hipparions and protohippines, which had been merrily evolving on their own paths.
During the first major glaciations of the late Pliocene (2.6 Ma), certain Equus species crossed to the Old World. Some entered Africa and diversified into the modern zebras. Others spread across Asia, the Mideast, & N. Africa as desert-adapted onagers and asses. Still others spread across Asia, the Mideast, and Europe as the true horse, E. caballus. Other Equus species spread into South America. The Equus genus was perhaps the most successful perissodactyl genus that ever lived -- even before domestication by humans.
For any unknown reason, the majority of horses in Northern America has died out in the beginning of last Glacial age and during late Pleistocene an era (approximately 11000 years ago) all staying horses Northern and South America have disappeared completely. It has been attributed to climatic conditions. America remained without horses while Spaniards have not brought them in XV century.
Early Horse Groups.
Since early prehistoric Equus Caballus, four separate types have developed. All these four types had the big influence on breeds existing today.
Pony Type 1 - is thought to have lived in northwest Europe. This horse was similar to what we know as Exmoors and Icelandic breeds today and was resistant to wet and cold. They were usually brown or bay and stood 12-12.2 hands.
Pony Type 2 - was much bigger than type one. It looked very similar to the Asian Wild horses and was also very resistant to the cold. It's modern counterpart might be considered to be the Highland Pony. These guys stood around 14 to 14.2 hands tall. They had a convex profile and were quite heavy and more stocky than type one. They inhabited northern Eurasia and due to it's built would have been a better trotter than runner. They were yellow to dun in color with a dorsal stripe.
Pony Type 3 - was a desert horse living in Central Asia. He survived the droughts and was resistant to heat. The desert horse has had a profound influence on the modern day horses offering speed, stamina and agility. The counterpart of today would be breeds like the Akhal-Teke. These horses measured 14.3 with long necks and ears, thin skin, and they were goose-rumped. His body was lsab-sdied and narrow and he was a bit coarse.
Pony Type 4 - was the protype Arabian standing about 12 hands high. He was not at all coarse like type three, was fine boned with a straight profile, refined head and a slight concave in the face. This too was a heat resistant desert horse, with a silky long mane and tail and fine body hair. It was native to western Asia and was noted for it's beauty, flat top-line and high tail set.
Modern Horse Groups.
Modern day classifications have become simplified from years past, now showing three main groups.
A Heavy Horse - is what we would refer to as draft breeds like the clydesdales, and belgiums. These horses today are used in all types of disiplines but originally were used more as agriculture assistants. These breeds are called cold-blooded and usually have deep chests and short thick legs and broad hooves. They are very strong but not very fast.
The Pony - as unique porportions. The body length exceeds it's height at it's withers and it's leg length usually equals it's depth. A pony stands less than 15 hands tall. Other distinctions in horses is made based on color, temperment and defining characteristics. Not all horses fit into these categories some like the cob, polo ponies and hacks are not classified.
The Light Horse - group is separted into horse and pony. The separation is determined primarily by size with a horse being anything 60 inches , 15 hands or taller. Horses are usually porportionate to their size and leg length whereas a pony is usually stocky in build and short legged. Horses in this classification have a sloped shoulder and narrow body. Thoroughbreds, Arabians and other hot blooded horses generally fall into this category. The exception here would be the "Warmblood" where does he go, this is usually determined by physical characteristics.
Cultivated about 3,000 years ago, the horse had deep influence on a human history in such areas as movings, an agriculture, war, sports, communication, and travel.