Question

Based on the phylogenetic tree in Figure 28.2, which of the following statements is correct?

(A) The most recent common ancestor of Excavata is older than that of SAR.

(B) The most recent common ancestor of SAR is older than that of Unikonta.

(C) The most basal (first to diverge) eukaryotic supergroup cannot be determined.

(D) Excavata is the most basal eukaryotic supergroup.

Short answer

1. The statement “the most recent common ancestor of Excavata is older than that of SAR” isincorrect.

2. The statement “the most recent common ancestor of SAR is older than that of Unikonta” isincorrect.

3. The statement “the most basal (first to diverge) eukaryotic supergroup cannot be determined” is correct.

4. The statement “Excavata is the most basal eukaryotic supergroup” is incorrect.

Step-by-step solution

Excavata

Excavata is a division of the eukaryotic supergroup. These organisms possess an excavated groove in the body, and hence they are named excavates. The three clades of organisms that are found within excavate include parabasalids, diplomonads, and euglenozoans.

Explanation of option ‘(A)’

The most recent form of excavata is those that possess flagellates. These organisms are often referred to as euglenozoans. These organisms are not older than SAR as they have evolved, and then these organisms developed flagella to enable locomotion.

Thus, flagellates are not older than SAR.

Therefore, the given statement is incorrect.

Explanation of option ‘(B)’

Unikonata is an organism that is placed under Excavata of the eukaryotic supergroup. These organisms are very ancient forms that diverged; they were one of the oldest forms to arise. Therefore, SAR cannot be older than Unikonata.

Thus, Unikonata is the most primitive Excavata.

Therefore, the given statement is incorrect.

Explanation of option ‘(C)’

The most basal or the first organism to diverge to produce a eukaryotic supergroup cannot be determined easily. This is because evolution might have caused many traits that were present in the past to go missing, and hence tracing back in time following the traits could be inappropriate.

Thus, the most primitive eukaryotic supergroup cannot be determined easily.

Therefore, the given statement is correct.

Explanation of option ‘(D)’

Excavates were one of the first groups to arise from as eukaryotes as they bridged a gap between eukaryotes. However, these organisms cannot be considered the most basal organisms because no evidence has been provided.

Many organisms that evolved prior to this might have become extinct and might not have left traces.

Thus, excavata is not the most basal eukaryotic supergroup.

Therefore, the given statement is incorrect.