Why do the three species have similarities and differences in their body structures, and how can Xiao use the structures to determine if the new fossil is more closely related to hippopotamus or green iguanas?

Xiao can use these structures to create a similarity matrix that enables to differentiate between synapomorphies and homoplasies .

Explanation:

A synapomorphy is a trait that has been inherited from the same ancestor, this trait enables to establish a relation of homology between two or more species; while a homoplasy is an analog structure that doesn't have homology.

you are certainly talking about this picture:

a: is the label of the white square, it is showing the  replication fork, formed by helicase (d) ==> so it is the site of dna separation and replication 

b: is a new dna brand that is following directly the replication fork, so it is continuous ==> built continuously from 5' to 3

c: dna polymerase cannot replicate dna on its own, it needs the of their proteins, and one of them plays the role of a clamp which fixes  the dna with the dna template and increases  the processivity of the enzyme. ==>   stops polymerase from falling off the  template.

d: is the enzyme responsible for forming the replication fork (helicase) ==> unwinds and separates dna into two strands

e: is the delayed strand, it is built  in the opposite sense of the helicase, so dna will be built in fragments ==> built  fragments from 5' to 3 joins

and finally f: is the enzyme that builds  the new dna strand (dna polymerase) ==>   adds nucleotides to make a new dna helix.

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c

explanation: