Kingdom: Animalia | Phylum: Chordata | Class: Mammalia | Order: Perrisodactyla | Family: Equidae
Genus: Equus | Species: Caballus
Genus: Equus | Species: Caballus
The pentadactyl limb is made up five digits on each leg but can appear different in many species that have one. They will appear different according to the animals’ environment, food source and means of travelling. The horse is a prime example of how the pentadactyl limb has evolved and adapted to its environment. The earliest ancestor which roamed the earth 60 million years ago was extremely small compared to the modern horse. It stood approximately 0.4 metres tall and was called the Eohippus, it had three main toes on the front feet with an additional toe further up the limb and three on the back feet. Each toe had a formation of ‘hooflets’ which at this point was the only main link to the modern horse. The Eohippus lived in marsh lands, jungles and rocky slopes of America which was difficult for grip and walking across but made easier with their separate toes. However their limbs did have a disadvantage which was lacking the ability to run fast.
Their front legs were shorter than the back making running difficult so their only way of escaping predators was to hide amongst the trees and foliage of the jungle. During the ice age a lot of the jungles had decreased in size making most lands open which for the slowest of the Eohippus didn’t work in their favour. A lot of them died out, leaving the faster of their species left. As the environment changed, evolution of the horse took over; over millions of years horses began to grow bigger, faster and stronger with better equipped senses. The Eohippus formed into the Miohippus and then to the Mesohippus whose toes were smaller. Because the ground was firmer during and after the ice age the horse began to walk on their toes which allowed them to reach greater speeds than that of the Eohippus, as well as turn quicker which was ideal if they were preyed upon.
The Mesohippus then evolved further into the Parahippus which was much larger in size and then into the Merichippus which was starting to look more horse like in figure. Due to their toes being used, the middle toe in particular they started to form the hoof and the outer toes began to disappear. The Pliohippus which has evolved from the Merichippus, only had one toe which was a fully formed hoof, this made it much easier and hard wearing to walk and gallop on the harder grounds that they roamed upon. The Pliohippus grew much taller and formed into the modern horse Equus, which stands 52 inches high, with long legs, large hooves to spread out the weight, thick neck and a long mane.