Imagine a scientist finds the fossils of an extinct Ichthyosaur and finds this morphological similarity of Ichthyosaurs and modern dolphins: bones indicating flippers and a tail for swimming. The scientist guesses that Ichthyosaurs may form a monophyletic group with the dolphins, based on this morphological similarity. What is one method or line of reasoning that scientists could NOT use when testing the hypothesis that dolphins and Ichthyosaurs form a monophyletic group?

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.