The horizontal axis of the cladogram depicted below is a timeline that extends from 100,000 years ago to the present; the vertical axis represents nothing in particular. The labelled branch points on the tree (V-Z) represent various common ancestors. Let's say that only since 50,000 years ago has there been enough variation between the lineages depicted here to separate them into distinct species, and only the tips of the lineages on this tree represent distinct species.
-Which of the five common ancestors, labelled V-Z, is the common ancestor of the greatest number of species, both living and extinct?
A) V
B) W
C) Y
D) Z

Question

The horizontal axis of the cladogram depicted below is a timeline that extends from 100,000 years ago to the present; the vertical axis represents nothing in particular. The labelled branch points on the tree (V-Z) represent various common ancestors. Let's say that only since 50,000 years ago has there been enough variation between the lineages depicted here to separate them into distinct species, and only the tips of the lineages on this tree represent distinct species. 
-Which of the five common ancestors, labelled V-Z, is the common ancestor of the greatest number of species, both living and extinct?
A) V 
B) W 
C) Y 
D) Z

Quizplus · Accepted Answer

Common ancestor Y is the common ancestor of the greatest number of species, both living and extinct, as its lineage has evolved into three distinct species (X, Y1, and Y2). The other common ancestors have only given rise to two distinct species or less.

The Horizontal Axis of the Cladogram Depicted Below Is a Timeline