Answer:
The correct answer is - Take blood samples and use DNA evidence to determine a more complete phylogenetic tree .
Explanation:
Scientists could not use DNA evidences to make a complete phylogenetic tree of Icthyosaur as there are no blood samples or other DNA molecules to create DNA printing or mapping to create phylogeny with the modern dolphins. They only can be make similarities based on the morphological characteristics of these two groups.
Thus, the correct answer is - Take blood samples and use DNA evidence to determine a more complete phylogenetic tree .