The Hyracotherium: The Evolution Of Horse

Living organisms survive due to their ability to adapt to their environment through natural selection. Horses have existed for millions of years, but observing a Hyracotherium, we may have not been able to recognize it as a horse due to the changes that have occurred since the Eocene epoch. These changes in environment have changed the equine morphology to improve its fitness to the horse we understand today by changing its skull, teeth, and limbs. Hyracotherium fossils suggest that this horse lived about 55-45 million years ago during the Eocene epoch when the environment consisted of thick and closed canopy forests. According to our data, we found the skull length, rostrum length, masseter length, and the mandible depth was much smaller, …show more content…
A change in environment caused a change in favorable characteristics as the teeth and jaws of Merychippus evolved. The length of the mandible, rostrum, and masseter more than doubled from the Hyracotherium. This increase in length aids the Merychippus to chew tougher foods with more teeth. This caused the transition of the horse to become grazers over browsers. The tooth height and length also doubled and became more molarized and ridged. The increase in tooth size and change in tooth shape helped Merychippus to grind their food easier, as grass became their main food source. The change of the environment to grasslands cause the horse to evolve their jaws and teeth to adapt to their new food …show more content…
As the horse got larger, larger limbs were required to support its increasing size. From Hyracotherium to Equus, the central metatarsal length and width almost quadrupled, and the number of toes reduced from three toes to one hoof. These new characteristics allowed the horse to avoid predators in the new grassland environment better. Longer limbs allowed the horse to run faster and for longer periods of time, and with less toes, there was less muscle weight to drag their speed. These adaptations contained trade-offs, since it reduced the ability of the horse’s dexterity and agility, but since their environment no longer contained many forests and trees, they didn’t necessarily need these characteristics. A change in environment didn’t only change the diet and teeth of the horse, but it also changed the horse’s body to adapt to the ways it could move.
From Eocene to Holocene, the horse has adapted drastically from its skull, teeth, and limbs. The change from thick forests to open grasslands cause the overall size of the horse to increase. The teeth became more molar and ridged to account for better grinding of grass and the skull size allowed for more teeth. The limbs became simpler to account for the horse’s need to move faster and escape predators. These changes show how natural selection favored specific adaptations according