Question

A phylogenetic tree representing the evolutionary relationship between various vertebrates is shown below. Given this tree topology, which one or more of the following statements is/are correct?

• A. Crocodiles are more closely related to turtles than they are to dinosaurs.
• B. Mammals represent the outgroup with respect to reptiles.
• C. Dinosaurs are more closely related to crocodiles than they are to birds.
• D. Reptiles are nested within mammals.

Hint:

When interpreting phylogenetic trees, the placement of branches can reveal insights into evolutionary relationships. An outgroup helps in rooting the tree and understanding the ancestral traits and derived traits within the tree.

Answer 1

The Correct Option is B

Step 1: Understanding Outgroups. In phylogenetic trees, an outgroup is a group of organisms that serves as a reference group for determining the evolutionary relationships among the ingroup, or the main group under study. The outgroup is generally considered less closely related to all members of the ingroup. 
Step 2: Examining the Tree Topology. From the given tree, mammals are positioned as a separate branch outside of the major clade that includes reptiles (snakes, lizards, turtles, crocodiles) and birds (also considered evolutionarily as part of dinosaurs). This indicates that mammals are the outgroup with respect to the reptiles and birds, which form the ingroup in this evolutionary scenario.