Scientists are studying the evolutionary history of two closely related mammal species. They identify the earliest known evidence of each species and the most recent bones of the presumed common ancestor. The data is recorded in the chart.
|Common Ancestor Bones||Species 1 Bones||Species 2 Bones|
|Location||Asia and North America||North America||Asia|
Based on the data, which of the following is a reasonable estimate of when populations of the common ancestor became reproductively isolated?