Threshold of the Quaternary
At the start of the Ice Age a three-toed species of horse called Hipparion roamed the grass plains of Africa, Asia and Europe.
Glaciation and Melting Changing climate Scientists call the period in the Earth’s history between 2.6 million and 11,000 years ago the Pleistocene epoch. This period of over two and a half million years is popularly known as the Ice Age. During this time, the last wave of glaciation began when the ice sheets covered large areas of the planet. However, the climate during the Pleistocene was not always the same. Colder phases called glacial periods alternated with warmer interglacial periods. One reason for this is thought to be changes in the Earth’s orbit around the Sun over tens or hundreds of thousands of years, which means that at times the Earth moves closer to and then moves further away from the Sun. During the glacials it was further from the Sun, which caused the temperature to drop and resulted in a cool, dry climate. The polar regions and large continental areas were covered by thick ice sheets. In warmer periods, the ice sheets receded due to the rainier temperate climate. At present we are living during a pleasant interglacial phase, and scientists believe the next glaciation may begin 3,000 years from now. Interglacial in Europe 2.5 million years ago
In glacial periods the continental ice sheet reached up to 3 km thick in places. The glaciers, large slowly moving rivers of ice, in mountain valleys also grew and carved the landscape in their path with the large stones they carried with them down to the valley.
Migrating ice and flora In glacial periods the polar ice sheets expanded towards the equator, and the glaciation extended as far as the Alps and the Carpathians in Europe and the Great Lakes in North America. Because of the cooler climate, the vegetation zones shifted southwards. Most of Eurasia was covered in tundra with dwarf willows, birch, mosses and lichens. Around the Mediterranean the temperate climate produced grassland with a sparse covering of trees and bushes. As the climate grew warmer, the ice sheets shrank and forests sprang up on the grass plains. As glacials and interglacials alternated, the vegetation zones migrated to the north and south accordingly.
The world of giants
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Homo sapiens, or “wise man”, appeared during the first epoch of the Quaternary period, the Pleistocene. We are living in the second, recent epoch called the Holocene.
Glacial period in Europe 18,000 years ago
Ice Age > Threshold of the Quaternary > Glaciation and Melting
As the vegetation zones shifted when the ice sheet began to expand, animals lost TRIASSIC 251 million their habitats and they also had to struggle with the cold and lack of food. Sessile years ago organisms and slow-moving animals were unable to adapt and perished. Faster moving species migrated south or found refuge in small ice-free areas. Individuals of the same kind of animal found sanctuary in different places and each group began to evolve in isolation from each other. When the ice eventually receded, the separately evolved animal groups returned to their original habitat but were no longer able to breed with each other, that is to say they had become different species. The constant migration probably played an important role in the development of the migration of birds. Even today migratory birds fly south from the advancing cold and from the shortage of food, and return with the warmer weather in spring.
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The 3 metre tall Aepyornis, also known as elephant bird, weighed 400 kg and was the world’s largest bird.
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Beringia
Signs of the past
Migratory route Looking at a map of the Arctic today shows that Asia and America are separated by sea. Nowadays the distance between the two continents seems impossible to cross, but these two landmasses have been linked by a land bridge several times over the last 70 million years of the history of the Earth. This also happened in the Pleistocene. In the glacial periods the snow and ice accumulated on the continents and did not melt for a long time. This made the sea level fall by over 100 metres and the beds of the shallow Bering and Chukchi Seas became dry land in part. This created the Bering land bridge linking America and Asia, in places up to 1,000 km wide, which provided a migratory route for land animals. Camelids and equids crossed from North America to Asia, while musk ox, bison and mammoths, which evolved in Asia, as well as most probably humans went in the opposite direction.
Arctic ground squirrel
Triumphal march of the camelids An important part of the evolution and development of the species of the camel family took place in North America. The first camelids lived well before the Pleistocene and were the size of rabbits. Later, larger species reached South America, where they evolved into llamas and related species. The animals in this family which migrated across the Bering land bridge were the ancestors of one- and two-humped camels. Although today camels are desert animals, in the Ice Age five species lived in the tundra and grass plains of North America. One of them was the camelops, which lived in small family groups foraging in herds of 5 to 20 animals. In winter they grew a thicker coat and fed on fruit and leaves as well as grass. Although camelids are now extinct in their place of origin, North America, they survive today in Asia and Africa thanks to the Bering land bridge.
Reindeer evolved some one and a half million years ago in the North American part of Beringia and spread to Eurasia by crossing the Bering land bridge.
With a body length of 2.5 metres, the American lion was the largest land predator in North America during the Pleistocene. Its ancestor was probably the cave lion, which migrated to the continent via the Bering land bridge.
The spread of equids Equids, the members of the horse family, originated in North America. The earliest known horse, Eohippus, was the size of a fox and lived in the marshy forests of North America 60 million years ago. It still had toes and grazed on foliage. Over the next few ten million years the horse-like animals that evolved from it took possession of open grassy areas, switched to eating grasses and developed hooves instead of toes. By the Ice Age, two evolutionary lines had come into being in North America. One included smaller animals with thin legs resembling the Asiatic wild donkey and the other had characteristics pointing towards the modern horse. Some of the latter crossed the Bering land bridge from North America at the start of the Ice Age and populated Eurasia and Africa. Their descendants are the wild asses, zebras and wild horses. At the end of the Pleistocene equids went extinct in North America and horses were only reintroduced by Europeans in the 16th century. Asia
Forest musk ox, woolly mammoth and steppe bison migrated from Asia to America, and the Arctic camel and wild horse went in the opposite direction.
America
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Ice Age > Threshold of the Quaternary > Beringia
Bering land bridge
Great American Interchange
Titanis is the only known terror bird genus which migrated to North America during the faunal interchange and whose fossil remains have only been found there.
The Isthmus of Panama For millions of years life evolved separately in North and South America. A deep-water channel between the two continents linked the Atlantic and Pacific Oceans. As two plates met in this area deep beneath the ocean, there was volcanic activity when they rubbed together. Over time, a number of volcanic islands rose from the sea, and sediment coming from the two continents and deposited by ocean currents gradually filled the channels between the islands. This created a narrow strip of land, the Isthmus of Panama, 3 million years ago, which connects North and South America today. The formation of the land bridge had two major consequences. The ocean currents which had previously flowed through the channel altered direction, contributing to a change in the climate and the onset of the Ice Age. The other important change was that land animals were free to move from one continent to the other, starting the Great American Faunal Interchange.
The body of Toxodon, a 2.7 metre long herbivore of the South American grasslands, resembled that of a rhinoceros, while it had the head of a hippopotamus. Sabre-toothed cats coming from the north may have been a factor in its extinction.
Before the Great American Faunal Interchange the main enemies of the South American herbivorous Macrauchenia were terror birds, but later Smilodon, a sabre-toothed cat, also had this role.
The isolated continent For 150 million years South America was an island. This allowed many primitive animal groups to survive there for a long time. One example was the Phorusrhacidae family, commonly called terror birds, which filled the role of the apex predator on the continent. These flightless birds reached a height of 2.5 metres, running at 65 km per hour in pursuit of their prey and downing victims with their huge hooked beaks. The herbivores were also large. For instance, Glyptodon, a giant armadillo, was up to 3.3 metres long, the size of a car. Its relatives that are living today such as the nine-banded armadillo are far smaller. At the time of the faunal interchange armadillos, porcupines and, among the marsupials, opossum migrated northwards from the southern continent and are now part of the fauna of North America.
North America
Among other animals, sabre-toothed cats, tapir, deer, peccary and Cuvieronius, a member of the Gomphotheriidae family, migrated to South America, while Megalonyx, an early sloth, armadillos, capybara and porcupines left their home and arrived in North America.
Because North America was joined to Eurasia by Beringia on a number of occasions, most groups of modern animals were already present in the fauna before the interchange. Species in the rabbit, mouse, fox, bear, cat, peccary, tapir and camel families, animals that are typical of the fauna today, all made their way south from here. The new arrivals from the north adapted to their southern habitat so successfully that they account for half the mammals of South America. However, not all managed to establish themselves in the long term. Such a case is the mastodon, an elephant-like herbivore with tusks and a trunk. Perhaps the biggest change was caused by the predators which arrived from the north: the jaguar and puma, which survive to this day, and the extinct sabre-toothed cats and American lion, which became serious rivals to terror birds that went extinct.
The world’s largest rodent
South America
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Ice Age > Threshold of the Quaternary > Great American Interchange
Home of the modern mammal
Overview of the Pleistocene
In the Lower Pleistocene most of Europe was covered in vegetation that formed part of the mammoth steppe whose wildlife seems exotic compared to today’s. Besides the southern mammoth, Etruscan rhinoceros, Stenon zebra (Equus stenonis), gazelle (Gazellospira torticornis), giant tortoise (Cheirogaster) and an extinct relative of the raccoon dog Nyctereutes Megamastoides lived there.