evolution Homework draft

Question 1: The fossil needed to support the phylogeny is a common ancestor of both the hippo and the whale and would have characteristics of both.  Specifically it would have the pulley shaped astragalus. The common ancestor of the whale and hippo diverged and created 2 seperate species, hippo and whale, and did this by the hippo keeping its pulley shaped astragalus and the whale losing the pulley shape.  The common ancestor is some sort of combination that contains the pulley shaped astragalus but also some characteristics of the whale. The requirement for the pulley shape is because it would be near impossible for the common ancestor to evolve from a pulley shaped astragalus ancestor and then lose that trait only to gain it back in the hippo but not in the whale.  It makes much more sense to say the common ancestor contained the pulley shaped astragalus.

Question 2: The definition of homology is a characteristics that is shared or very similar among different species shared by their one common ancestor.  The definition of homoplasy which is, shared characteristics between species that wasn’t present in the common ancestor, is shown in the phylogeny when both the monotremes and the Therians both develop the unattached bone even though their common ancestor had the bone attached to the jaw.  This is a basic example of homoplasy and is likely due to living in similar conditions and having somewhat similar behaviors that benefited having an unattached bone. The phylogeny shows homology with the evolution of the 3 inner ear bones. Up until the Morganucodon the species all have the same inner ear and have it attached and to the lower jaw bone.  This shows homology because the ancestor is passing on its genes and the species has the same inner ear as their ancestor. One specific example is how the red bone keeps getting smaller, it happens to all the common ancestors as the time goes on and when the therians and monotremes both have very small red bones and a very similar shaped green bone which are both derived from their common ancestor meaning those traits are homology traits.