Question

4) Lastly, look at the oldest known ancestor of the modern-day horse, Eohippus, and the domesticate horses we see today a. List the features these 2 species have in common. How have modern day horses retained these traits over the last 55million years? Are they beneficial in some way? Do they not impact survival at all and therefore, natural selection isn't playing a role? Give a brief explanation for each retained trait between these 2 species b. List the features that have changed over the last 55 million years. How have these features changed and what were the selective pressures that drove those changes? Has the environment changed causing the different feature to be selected for? Has the community change causing some selective pressure based off of the animal's ability to get food or avoid predators? Give a logical explanation as to why natural selection chose these differences to evolve.

Answer 1

ANSWER A :-

1. The modern horse is called as Equus cabalus and the oldest known ancestor of this modern horse is the Eohippus.
2. There are many significant changes that have occured in the body morphology of the ancestral species which provided benefits to the modern horses helping in their survival.
3. The only similarity can be seen in case of the hoof like structures that can be seen in case of both the animals. These are called as hooflets. There were 4 toes on the forelegs and 3 toes on the hindleg and these were provided with a keratinized structure which formed the hooves and this has been modified in case of the modern horses in which there is a single centrally placed structure (hoof like) and this is the structure which is similar to the ancestral horse.
4. This structure has been modified into a single hoof like structure mainly to enhance the stability of the body or to focus the body weight on a single toe which in turn helped the horses to run faster and to balance the body weight.
5. This can be considered as an example of natural selection in which the nature favours the best characters which helps the animals to adapt and survive the changing conditions. In case of the modern horses, the single hoof is located centrally and this has been evolved as a part of disappearance of the remaining hooflets in the form of vestige and all these changes were associated with the increase in the length of the limbs along with fusion of certain portions of bones and changes in the brain size and the teeth structure.
6. This retained character of hooflet is thus the source of natural selection in horses making them better at escaping the predators rather than hiding as was observed in the ancestral species.

ANSWER B :-

1. The first modification that needs to be mentioned is the length of the teeth and the availability of crowns on the teeth. This modification made the modern horses adapt to the changing land structure which was made suitable for grazing rather than the Eohippus that fed on whatever it was able to eat. The teeths were modified in a manner taking into consideration the adaptation to cut the grass blades that would ease the process of digestion.
2. The main reasons for this change include the changes in climate and the migration of the animals apart from the changes in the eating habits which have already been mentioned in the first point. The crowns of the teeth were modified in a way so as to enhance the movement of the lower jaw to cut the grass blades.
3. Another modification that needs to be mentioned is the change in the size of the brain and the size of the hindlimbs. In the ancient species, the forelimbs were shorter than the hindlimbs which in turn restricted their ability to run faster as compared to the modern equines which have modification in the length of bones of both the limbs to mediate a faster motion of the animal. The number of fissures in the brain of the modern horses indicate the changes in the brain size and the number of fissures in the modern horses. The more these structures, more will be the highlighted intelligence associated with the animal and this is associated with search for new food sites or change in eating habits which are associated with the changes in the teeth morphology.
4. As already stated above, the changes that have occured in all the above mentioned cases have occured with respect to the changes that occured in the surroundings as well as changes in the habits of the animal which lead to modification of certain structures which helped them to adapt and survive the extreme conditions which have led to the extinction of many intermediate species during the evolutionary period. As stated in the first question, changes hooves has been associated with escaping predation.

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