62:3.7

These mid-mammals were the first to exhibit a definite construction propensity, as shown in their rivalry in the building of both treetop homes and their many-tunneled subterranean retreats; they were the first species of mammals ever to provide for safety in both arboreal and underground shelters. They largely forsook the trees as places of abode, living on the ground during the day and sleeping in the treetops at night.