Examination of fossil records for trees and small mammals in North America for the past 20,000 years revealed which of the following (choose all that apply) ?
a) Many species that occur in the same community today, did not occur together during prehistoric times
b) As Ice Ages came and went, species changed their geographic range independently of other species
c) Many species that occurred in the same community during prehistoric times, do not occur in the same community today.
d) Some species experienced significant evolutionary changes in response to climate shifts over the past 20,000 years.