The Origin of Horses From the Very Beginning

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To begin, horses are a member of the taxonomic family known as Equidae, fossils indicate the very first ancestor to have lived a little over 52 million years ago. Beginning in the Eocene Epoch which ranged between 36 to 56 million years ago, the modern day horses’ first ancestor was believed to be the Eohippus, also known as the “dawn horse”. The Eohippus is a part of ‘early equids’ which ranges from the Eohippus to the Miohippus. They mostly resided in North America but fossils show they also lived as far as in Europe.

Unlike the large, muscular, and fast horses we know today these mammals were much smaller and were compared to be the size of modern day foxes. But, they did have longer hind limbs which were early signs of adaptations to running. Then came the Orohippus, and Epihippus, which were similar in size. It wasn’t until the Mesohippus and Miohippus that we see a slightly larger size, a less arched back, and changes in muscles and joints.

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Moreover with the passage of time, came the group of ‘true equines’ which ranged between the Kalobatippus to the Plesipuss. These mammals lived between the Miocene which was a little over 23 million years ago to the Pliocene which was over 5 million years ago. The mammals within Kalobatippus, Parahippus and later Pliohippus resembled the size of a small pony. They slowly began to resemble the size of modern day horses, especially the populations of Dinohippus and Plesippus. Dinohippus was considered to be close to the horse as its body mass ranged from 500 to 1300 lbs, unlike previous generations.

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The Plesippus was the most recent ancestor, and its body mass was similar to that of an Arabian horse, it was sketched to be a hybrid of a zebra and horse.

As a result, this brings the modern day horse. It lies within the genus of Equus, and contains some relatives including the zebra and donkey. Modern day horses evolved from the small fox like mammal to the much larger and taller animal we know today. As a result of the slow evolution in size, it is evident horses adapted to their outside environment. The change from stockier legs to slimmer legs, and slimmer torsos can be held accountable for advancement in their agility and speed. These mammals evolved from a much smaller, almost donkey like form, to a much stronger and taller body. They evolved both in size and shape, especially within their limbs and necks being slimmer and stretched out more. This demonstrates how over time the modern day horse has evolved as a result of changes in body size.

Four of which were small proto hooves, and the thumb was off the ground. On its hind limbs it had small hooves on three of its five toes, while the thumb was also off the ground. Changes could then be seen in the Orohippus when it maintained the padded foot but lost its vestigial toes, so now it had four toes on each forelimb and three toes on each hindlimb. Then the gradual changes of having only three toes on each limb resulted in the mammal developing a stronger middle toe where it put most of its weight and strength into. This is demonstrated in the fossils of the Mesohippus up until the modern day horse.

Furthermore the changes in toe number can be attributed to the changes in their environment. For instance in prairie-dwelling species they developed hooves and longer legs to help them run faster from predators. As opposed to forest-dwelling species who developed shorter legs and three toes to allow them to walk a softer ground. It is believed that over 30 million years ago a drastic change in weather patterns caused for the populations of mammals with longer limbs and fewer toes to survive. This largely illustrates how the horse’s ancestors once had more toes but overtime developed less in response to the environment they lived in. Horses now mainly have one strong middle toe or hoove with the two side toes. Similar to dogs, you can find the fourth toe sometimes but it is no longer in use so it is very small, just like a dogs thumb which usually hangs above their paw.

Similarly, the most notable form of evidence for the evolution of horses is a result of their molars and skull structure. Many who studied the evolutionary history of the horse, were able to see similarities in species and draw connections due to horse teeth fossils. A large portion of researchers found that teeth evolved over time as a result of climate change which changed the vegetation available for the mammals to eat. For example, during primitive Eocene horses had short, dull, and bumpy crowned teeth used for eating soft vegetation. The Eohippus had 44 crowned teeth, four premolars, and three molars on each side of the jaw. The most dramatic change came with the Orohippus, which its last premolars moved and developed into molars. Researchers believe this was a result of eating tougher plant material. Millions of year later with the Epihippus, Mesohippus, Miohippus, they began to develop tougher teeth and had slowly developed well formed crests on their teeth.

Overtime, the ‘true equines’ had developed teeth that resembled more of the modern day horse. Beginning with the Parahippus, they had much more prolonged faces and its four premolars were similar to horses molars. Their incisor teeth also developed crown crests similar to humans. A few million years later came the Merychippus, had wider molars which were believed to have been a result of grazing. A large number of horses evolved high crowned teeth used for grazing a more extensive type of grass. As soon as, high crowned teeth evolved, a large number of horses underwent a second phase of adaptation, grazers became mixed feeders. This type of adaptation was found through fossils which contained carbon isotopes, demonstrating that the horse evolved and changed due climate and diet.

As a result, if the climate underwent change, so did the horses’ diet which can be seen through the development of their teeth. They lived in forested environments filled with warm and moist air, but as they moved from their environment, their diets changed. Resulting in sharper points in their teeth associated with a diet of leaves which is what today’s horses’ diets consist of. With such changes in the teeth, horses underwent changes in their bone structure particularly in the skull, to accommodate larger teeth. Horses developed longer faces and a deep mandible.

Updated: Jan 26, 2022
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The Origin of Horses From the Very Beginning. (2021, Dec 11). Retrieved from https://studymoose.com/the-origin-of-horses-from-the-very-beginning-essay

The Origin of Horses From the Very Beginning essay
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