Geological evidence indicates that two landmasses became separated by a deep ocean channel 45 million years ago and have been moving apart ever since. You are studying a group of organisms that is widespread as a native part of the biota on both of the landmasses. What can you conclude about the group's evolutionary history?
A)The group's ancestors were definitely present on the original landmass.
B)The group's ancestors cannot have been present on the original landmass.
C)If the group's ancestors could not move across the open ocean, it is very likely that they were present on the original landmass.
D)The group's ancestors must have independently colonized each of the landmasses from a third location within the past 45 million years.

Question

Quizplus · Accepted Answer

If the group of organisms is native to both landmasses and separated by a deep ocean channel, it is unlikely that they would have colonized the second landmass via long-distance dispersal. It is more likely that the group's ancestors were already present on the original landmass and were able to move across the channel before it became too deep or too wide to cross. Therefore, it is very likely that the group's ancestors were present on the original landmass if they are native to both landmasses.

Geological Evidence Indicates That Two Landmasses Became Separated by a Deep