Land elevation and sea segregation were slowly changing the world’s weather, gradually cooling it, but the climate was still mild. Sequoias and magnolias grew in Greenland, but the subtropical plants were beginning to migrate southward. By the end of this period these warm-climate plants and trees had largely disappeared from the northern latitudes, their places being taken by more hardy plants and the deciduous trees.
There was a great increase in the varieties of grasses, and the teeth of many mammalian species gradually altered to conform to the present-day grazing type.
25,000,000 years ago there was a slight land submergence following the long epoch of land elevation. The Rocky Mountain region remained highly elevated so that the deposition of erosion material continued throughout the lowlands to the east. The Sierras were well re-elevated; in fact, they have been rising ever since. The great four-mile vertical fault in the California region dates from this time.
20,000,000 years ago was indeed the golden age of mammals. The Bering Strait land bridge was up, and many groups of animals migrated to North America from Asia, including the four-tusked mastodons, short-legged rhinoceroses, and many varieties of the cat family.
The first deer appeared, and North America was soon overrun by ruminants—deer, oxen, camels, bison, and several species of rhinoceroses—but the giant pigs, more than six feet tall, became extinct.
The huge elephants of this and subsequent periods possessed large brains as well as large bodies, and they soon overran the entire world except Australia. For once the world was dominated by a huge animal with a brain sufficiently large to enable it to carry on. Confronted by the highly intelligent life of these ages, no animal the size of an elephant could have survived unless it had possessed a brain of large size and superior quality. In intelligence and adaptation the elephant is approached only by the horse and is surpassed only by man himself. Even so, of the fifty species of elephants in existence at the opening of this period, only two have survived.
15,000,000 years ago the mountain regions of Eurasia were rising, and there was some volcanic activity throughout these regions, but nothing comparable to the lava flows of the Western Hemisphere. These unsettled conditions prevailed all over the world.
The Strait of Gibraltar closed, and Spain was connected with Africa by the old land bridge, but the Mediterranean flowed into the Atlantic through a narrow channel which extended across France, the mountain peaks and highlands appearing as islands above this ancient sea. Later on, these European seas began to withdraw. Still later, the Mediterranean was connected with the Indian Ocean, while at the close of this period the Suez region was elevated so that the Mediterranean became, for a time, an inland salt sea.
The Iceland land bridge submerged, and the arctic waters commingled with those of the Atlantic Ocean. The Atlantic coast of North America rapidly cooled, but the Pacific coast remained warmer than at present. The great ocean currents were in function and affected climate much as they do today.
Mammalian life continued to evolve. Enormous herds of horses joined the camels on the western plains of North America; this was truly the age of horses as well as of elephants. The horse’s brain is next in animal quality to that of the elephant, but in one respect it is decidedly inferior, for the horse never fully overcame the deep-seated propensity to flee when frightened. The horse lacks the emotional control of the elephant, while the elephant is greatly handicapped by size and lack of agility. During this period an animal evolved which was somewhat like both the elephant and the horse, but it was soon destroyed by the rapidly increasing cat family.
As Urantia is entering the so-called “horseless age,” you should pause and ponder what this animal meant to your ancestors. Men first used horses for food, then for travel, and later in agriculture and war. The horse has long served mankind and has played an important part in the development of human civilization.
The biologic developments of this period contributed much toward the setting of the stage for the subsequent appearance of man. In central Asia the true types of both the primitive monkey and the gorilla evolved, having a common ancestor, now extinct. But neither of these species is concerned in the line of living beings which were, later on, to become the ancestors of the human race.
The dog family was represented by several groups, notably wolves and foxes; the cat tribe, by panthers and large saber-toothed tigers, the latter first evolving in North America. The modern cat and dog families increased in numbers all over the world. Weasels, martens, otters, and raccoons thrived and developed throughout the northern latitudes.
Birds continued to evolve, though few marked changes occurred. Reptiles were similar to modern types—snakes, crocodiles, and turtles.
Thus drew to a close a very eventful and interesting period of the world’s history. This age of the elephant and the horse is known as the Miocene.