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“Lab Assignment #2 (Horse Evolution)”
Through fossil records from Hyracotherium to Mesohippus to Merychippus to Pleshippus to the Equus, one can see the development of dentition, limbs and skull based on the environment that the horses adapted to with time. Environmental changes from the Eocene to the Holocene brought about natural selection as the horses’ initial characteristics could not adapt. In order to survive, horses evolved traits such as stronger limbs, tougher teeth and others that best fit and adapted to their surroundings. In this lab, we examined these five horse evolution fossils to understand the change in equine morphology in relation to the habitat and the natural selection within the horse population. Hyracotherium, one of the fossils observed, has morphologic characteristics that suggest life in thick, closed canopy forests. The species’ dental characteristic, bunodont, is an indication of a browsers eating habit. In addition, the small skull, small rostrum and a short masseter implies a diet of easily chewable and digestible soft foods, like berries and nuts, mainly found in forests. Also, their digitgrade limbs are most adaptable to a habitat requiring more maneuverability than speed. In a thick canopy forest, speed would be unnecessary as there would be obstacles of trees, shrubs and wet grounds. Rather, maneuverability would be much more efficient in a forest where the surroundings are bushes, shrubs and trees. This type of limb also becomes easily fatigued and while that is dangerous in an open grassland, this quality is acceptable in a thick canopy forest where running is limited to short periods of time.

Beginning in the Miocene, as the climate became drier and cooler, the increase in grasslands influenced the morphology of horses teeth and jaw. Before the Miocene, horse populations showed signs of bunodont teeth that were meant for living in forests or areas plentiful of soft foods. However, the increase in grasslands evolved the...
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