Evolution

SBI 3U

February 22nd 2013

Evolution ISU Assignment #3

a) Draw a graph showing changes in the height of the horse over time.

(0 years is the modern day horse and so on)

b) Describe changes in the leg length and the width of the digits

As time progressed the length of the horses’ legs increased (aiding in the change in height displayed in the previous question). The digits became narrower as time progressed until they became dormant in the modern day horse. From the diagrams the actual resulting digit in the modern day horse ended up being wider.

c) Do horses have thumbs and fingers? Explain.

The earlier ancestors of the horse (Hyracotherium, Mesohippus and Merychippus) had multiple appendages. The modern day horses have one appendage; the hoof. During evolution the appendages began to shrink in size until they became dormant, leaving the horse with one main visible digit.

Case Study Application Questions:

1) Hydracotherium lived in a dense forest area dominated by a rich undergrowth of ferns. What do you think the advantages of small body stature might be in this type of environment?

Small body stature in this type of environment may have allowed for protection from predators in the senses that it makes it easier to evade predators; being smaller and more nimble as well as making it easier to use your surroundings to hide from predators; hiding amongst the undergrowth.

2) A change in vegetation to grasslands brought about changes in the shape of the horses legs. What changes in vegetation could have caused the evolution of the horse?

Since the environment went from eating leaves or other vegetation off of bushes and trees to eating grass this would cause a change in a horses teeth. Since grass is courser than leaves the tooth structures changed, becoming more flattened. The legs and neck of the horses were also affected because the horses that lived in the grasslands and grazed on grass needed longer necks to reach the ground where the grass...