Paper 61 Overview: The Mammalian Era on Urantia

The mammalian era on Urantia spans almost fifty million years, beginning with the appearance of placental mammals and concluding with the end of the ice age. During this Cenozoic age, earth's landscape showcased rolling hills, broad valleys, wide rivers, and great forests, with the Panama isthmus and Bering Strait land bridge rising and falling multiple times. This period witnessed the successive dynasties of mammals evolving and competing for dominance across a changing world of shifting continents and climate patterns.

The mammalian era chronicles the rise of mammals from their reptilian ancestors through various evolutionary stages, leading eventually to the precursors of human beings. The era concludes with the ice age, which dramatically shaped earth's surface and created the conditions that would influence early human development. Through six distinct glacial periods spanning two million years, ice sheets advanced and retreated across North America, Europe, and parts of Asia, creating the Great Lakes and other significant geological features that remain today.

The era of mammals extends from the origin of placental mammals to the end of the ice age, covering a period of slightly less than fifty million years. During this Cenozoic age, the world presented an attractive appearance with rolling hills, broad valleys, wide rivers, and great forests, while the Panama isthmus and Bering Strait land bridge repeatedly rose and fell. The animal world thrived with varied species, with birds swarming in trees and the entire planet functioning as an animal paradise despite the constant struggle for supremacy among evolving animal species.

The accumulated deposits from the five periods of this fifty-million-year era contain fossil records that document the successive mammalian dynasties. These records trace evolutionary development straight through to the appearance of humans, providing evidence of the gradual progression from early mammals to the emergence of human beings. These fossil layers tell the story of life's advancement during what scientists call the Cenozoic era.

Fifty million years ago, the land areas of the world were generally above water or only slightly submerged, with formations and deposits from this period being both land and marine in origin. Land gradually rose while simultaneously being eroded and washed down to lower levels and toward the seas. Early in this period, placental mammals suddenly appeared in North America, constituting the most important evolutionary development up to that time, springing directly from pre-existent reptilian ancestors that had persisted through the dinosaur decline.

Mammals possessed significant survival advantages over other life forms, including their ability to bear relatively mature offspring, protect and nurture their young with affection, employ superior brain power, utilize increased agility to escape enemies, and apply superior intelligence to environmental adaptation. As this period progressed, many new mammalian species developed, including small horses, rhinoceroses, tapirs, primitive pigs, squirrels, lemurs, and monkey-like animals, all adapted to living in mountain forests. These early Cenozoic mammals inhabited land, water, air, and treetops, possessed multiple mammary glands, were covered with hair, developed two sets of teeth, and had large brains relative to their body size.

This period featured rapid evolution of placental mammals, with more progressive forms of mammalian life developing from earlier species. Although early placental mammals descended from carnivorous ancestors, herbivorous branches soon developed, followed by omnivorous families. Most modern land flora, including the majority of present-day plants and trees, had already appeared during earlier periods and now provided food for the rapidly increasing mammals.

Over time, more than one hundred species of primitive mammals became extinct as evolution favored animals with larger brains and greater agility rather than armor and size. Various mammalian groups emerged during this period, including the ancestors of dogs, cats, rodents like beavers and squirrels, and hoofed grazing animals. Some placental mammals even abandoned land for ocean life, becoming the ancestors of modern whales, dolphins, and seals. By the close of this Oligocene period, which lasted ten million years, plant life and land animals had largely evolved to forms very similar to those existing today, with subsequent epochs mainly characterized by specialization of already established types.

Land elevation and sea segregation slowly changed the world's weather, gradually cooling it, though the climate remained mild. Warm-climate plants began migrating southward, and by the period's end, subtropical plants had largely disappeared from northern latitudes, replaced by hardier plants and deciduous trees. Grasses increased in variety, causing many mammalian species to develop teeth adapted for grazing as land continued rising and climate patterns shifted.

Twenty million years ago marked the golden age of mammals, with the Bering Strait land bridge enabling animal migrations between Asia and North America. Huge elephants with large brains dominated most of the world except Australia, while North America became home to ruminants like deer, oxen, camels, bison, and rhinoceroses. The horse brain ranked second only to elephants in animal intelligence, though horses never fully overcame their instinct to flee when frightened. This period also saw the evolution of true monkeys and gorillas in central Asia, though neither species was directly involved in the ancestral line that would later lead to humans. The biologic developments during this era contributed significantly toward setting the stage for humanity's eventual appearance.

This period witnessed widespread preglacial land elevation across North America, Europe, and Asia, dramatically altering topography with new mountain ranges, changed stream courses, and isolated volcanic activity worldwide. For a brief time, all land on earth was connected except for Australia, enabling the last great worldwide animal migration. North America linked with both South America and Asia, allowing free exchange of animal life, with Asian sloths, armadillos, antelopes, and bears entering North America while North American camels migrated to China.

Life from the preceding period generally continued to evolve and spread, with the cat family dominating animal life while marine life remained relatively static. Five million years ago, the horse evolved to its modern form and spread worldwide from North America, though it later became extinct on its continent of origin. Climate gradually cooled, causing land plants to move southward and eventually stopping animal migrations over northern land bridges. Soon after, the land connection between Africa and South America submerged, isolating the Western Hemisphere as we know it today. This ten-million-year period concluded without the appearance of human ancestors, and is known scientifically as the Pliocene.

By the previous period's end, northeastern North America and northern Europe had risen significantly, with some North American areas elevated up to 30,000 feet. These northern regions had previously enjoyed mild climates with ice-free arctic waters, but shifting ocean currents and seasonal winds created constant precipitation over the northern highlands. Snow accumulated on these elevated, cool regions until reaching depths of 20,000 feet, eventually metamorphosing into solid, creeping ice that formed massive glacial sheets.

The glacial ice was distributed with half in North America, one-fourth in Eurasia, and one-fourth elsewhere, primarily Antarctica. Northern regions experienced six distinct ice invasions with numerous advances and recessions associated with each sheet. The first North American glacier began its southern advance two million years ago, taking nearly one million years to complete its cycle of advance and retreat. Subsequent glaciers followed, with varying degrees of coverage and impact on the landscape. Between glacial periods, the climate was milder than today, while during active glaciation, enormous icebergs slid off coastal regions into the surrounding seas, dramatically affecting regional environments.

The great event of this glacial period was the evolution of primitive humans. Slightly west of India, on land now submerged, dawn mammals appeared among descendants of North American lemur types. These small animals primarily walked on their hind legs and possessed large brains proportionate to their size. Through successive mutations, mid-mammals emerged, followed by the Primates, and finally human beings. This evolutionary sequence occurred alongside a parallel development that produced the simian ancestry, with human lineage always advancing while simian tribes remained stationary or retrogressed.

One million years ago, a mutation within the progressing Primates suddenly produced two primitive human beings, the actual ancestors of mankind. This momentous development coincided with the beginning of the third glacial advance, placing humanity's birth in a challenging, invigorating environment. Early humans were not present in the Western Hemisphere until near the ice age's conclusion. During interglacial periods, they migrated westward around the Mediterranean and gradually spread across Europe, leaving evidence of their presence in western European caves where human bones have been found alongside remains of both tropical and arctic animals.

Throughout the glacial period, while ice activity dominated northern latitudes, other geological processes continued worldwide. Glaciers left distinctive evidence across the landscape, including boulders, surface cleavages, lakes, displaced stones, and rock flour. They created surface undulations called drumlins, displaced rivers, and completely transformed the terrain, leaving behind ground, lateral, and terminal moraines as telltale signs of their movement and reach. The fourth ice sheet, uniting the North American central and eastern fields, extended as far south as Illinois and Pennsylvania.

The sixth and final glaciation began 250,000 years ago, representing the period of greatest snow deposition despite the beginning subsidence of northern highlands. This massive ice sheet coalesced from three centers into one vast mass, with western mountains participating in the glacial activity. During its retreat, this glacier carved out the present North American Great Lakes system, which initially drained into the Mississippi valley, then eastward into the Hudson valley, and finally northward through the St. Lawrence route, which began functioning 37,000 years ago. The ice age formally ended about 35,000 years ago except in polar regions, roughly corresponding to the arrival of a Material Son and Daughter and the beginning of the Adamic dispensation, marking the start of the Holocene or post-glacial period.