Age of Mammals
Mammoths
Mammoths are extinct kinds of elephant, known for their long, curved tusks and, in later species, their shaggy coats. The most familiar species, the woolly mammoth, lived in northern lands during the Pleistocene Ice Ages and finally died out only a few thousand years ago. The woolly mammoth was just one of several species, all descended from the first kind, the South African mammoth, which evolved around 5 million years ago in southern Africa. Because the bodies of many mammoths became frozen soon after their deaths, many have remained extremely well preserved tens of thousands of years later when they are discovered. This is particularly true of woolly mammoths in the vast Siberian permafrost. For this reason, we know a great deal about how these animals lived.
Mammoth evolution
Paleontologists can identify different mammoth species from the pattern, shape and number of enamel ridges on their molars, their grinding teeth. The early, primitive species of mammoth had few ridges. The number of ridges increased gradually as new species evolved and moved out of Africa and into Eurasian grasslands, where they adapted to feed on tougher grasses and sedges.
African mammoths (Mammuthus africanavus), the second oldest species of mammoth, moved north out of Africa between 3.5 and 3 million years ago, spreading out across Europe and China. There they adapted to a wide range of different environments, including forests and grasslands. A new species, the southern mammoth (Mammuthus meridionalis), split off from African mammoths around 2.5 million years ago.
In East Asia, the steppe mammoth (Mammuthus trogontherii) evolved from the southern mammoth between 2 and 1.5 million years ago. The Columbian mammoth (Mammuthus columbi) evolved from a population of steppe mammoths that crossed into North America 1.5–1 million years ago. The woolly mammoth (Mammuthus primigenius) evolved from the steppe mammoth in East Asia around 400,000 years ago. It first reached North America about 100,000 years ago.
Mammoth tusks
All species of mammoth had gigantic, curved tusks, although those in females were smaller and thinner. In males, they may have been for display, both to attract females and to intimidate rivals. They were probably also used in fighting for territory or over mates. The males may have had pushing contests, interlocking their tusks. This sometimes led to them being snapped off. The curved shape of the tusks made them unsuitable for stabbing.
Tusks are actually modified incisor teeth that grew continuously throughout the mammoth’s life, as they do in a modern elephant. The tusks grew by layers—added yearly, weekly or even daily—so that, like the rings of a tree, they contain detailed records of their owner's life history. Thick layers (rapid growth) indicate rich summer grazing, while thin ones (slow growth) reveal low winter food supplies. Levels of certain chemicals in the tusks also provide evidence of the animal’s diet and can even give an indication of the climate of the time.
Southern mammoth
The southern mammoth roamed Europe and Central Asia in the Early Pleistocene Epoch, living from 2.5–1.5 million years ago. Measuring around 4 metres (13 feet) tall at the shoulder and weighing up to 10 tonnes, the twisted-tusk southern mammoth was one of the largest mammoths to exist. It lived during a time of mild climate in mixed woodland, including, for example, oak, ash and beech, where it grazed on leaves and shrubs.
Steppe mammoth
The steppe mammoth evolved in Asia around 1.5 million years ago, in the middle of the Pleistocene Ice Ages. It stood around 4 metres (13 feet) tall at the shoulder and weighed up to 10 tonnes. It was the first type of elephant to develop a hairy coat. It roamed across cold, bleak, dry grasslands south of the ice sheet feeding on coarse grasses. A bull's tusks could grow up to 5 metres (16 feet) long.
Columbian mammoth
The Columbian mammoth lived in North America from about 1.5–1 million years ago until around 11,500 years ago. It stood around 4 metres (13 feet) tall at the shoulder and weighed up to 10 tonnes. It had very long, curved tusks (up to 5 metres / 16 feet long) and four molars, which were replaced five or six times over the course of its lifetime. When the last set of molars wore out the animal was unable to chew, and so would die of starvation—as is the case with modern elephants.
The Columbian mammoth fed on sedge, grass, leaves, pine needles and other plants in areas of the United States and Mexico to the south of the mammoth steppe, the domain of the woolly mammoth (although the ranges of the two species probably overlapped and they may have interbred). The Columbian mammoth had a covering of fur, but it was probably less dense than that of the woolly mammoth.
Columbian mammoths lived in North America at the same time as Palaeo-Indians, the ancestors of Native Americans. These people hunted the animals for food. They used their skins for clothing and their bones for making tools and shelters. The mammoths were even depicted in rock art. The Columbian mammoth disappeared around 11,500 years ago. This may have been because of habitat loss as temperatures climbed after the last Ice Age, or because of hunting—or possibly a combination of both.
Pygmy mammoth
Between 80,000 and 13,000 years ago, mammoths lived on the Channel Islands of California (which lie about 10 kilometres / 6 miles away from the mainland). They were descended from a population of Columbian mammoths which must have swum or waded across from the mainland at a time when sea levels were lower.
These mammoths stood 1.7 metres (5.6 feet) tall at the shoulders—less than half the size of their mainland relatives. They had evolved to be smaller simply because, as their realm gradually shrank in size with sea levels rising once more, there was less and less food available. Some scientists consider them to be a species distinct from Columbian mammoths and call them pygmy mammoths or Mammuthus exilis.
Woolly mammoth
Woolly mammoths, with their shaggy coats and layers of body fat, were well suited to the cold, dry, environments of the far north. Woolly mammoths evolved from steppe mammoths around 400,000 years ago and roamed the northern tundra lands (also called the mammoth steppe) of Europe, Siberia, Canada and Alaska until about 11,500 years ago, when most of them died out. A small number managed to survive on Wrangel Island off the Siberian coast until only about 3700 years ago—nearly a thousand years after the Great Pyramids were built in ancient Egypt.
The woolly mammoth co-existed with early humans, who hunted (or scavenged) it for food and clothing and also used its bones and tusks for making tools, weapons, dwellings and carvings. Complete carcasses, well preserved in ice, are still quite commonly found today. Climate change—a rapid warming of temperatures led to a severe reduction of their habitat—probably finished the woolly mammoth, but it may have been hunted to extinction by humans.
The appearance of the woolly mammoth is probably the best known of any prehistoric animal, because of the existence of so many superbly preserved frozen specimens, as well as from paintings by humans who lived at the same time. Roughly the same size as a modern African elephant, a male woolly mammoth measured 2.7–3.4 metres (8.9–11.2 feet) high at the shoulder, and weighed up to 6 tonnes; females were slightly smaller. It was covered in fur, with an outer covering of long, coarse hair and an undercoat of shorter, slightly curly hair. Preserved woolly mammoth fur is reddish-brown, but this is thought to be the result of bleaching after the animal died. Recent studies show mammoths having either dark brown or blonde coats.
The woolly mammoth's ears were far smaller than those of modern elephants. This was an adaptation for cold weather: the small ears reduced heat loss and frostbite—its tail was short (just 36 centimetres / 14 inches) for the same reason. It mammoth had a large single-domed head and a sloping back with a high shoulder hump.
The woolly mammoth had very long, tusks (up to 4.2 metres / 14 feet long) curving until the tips pointed towards each other, sometimes crossing. It had four molars, two in the upper jaw and two in the lower. Like those of the Columbian mammoth, these were replaced five or six times over the course of the animal’s lifetime—around 60 years.
Like modern elephants, woolly mammoths were social animals and lived in matriarchal (female-led) family groups. They are likely to have formed large herds of thousands of individuals when they migrated across the wide open landscape. Adult woolly mammoths could easily defend themselves from predators with their tusks, or simply by being huge. But juveniles elderly or weakened adults were vulnerable to pack hunters such as wolves, hyenas and large cats.
Food at various stages of digestion has been found in the intestines of several preserved woolly mammoths, which reveals much about their diet. They ate mainly grass and sedges, along with flowering plants, shrubs and mosses, that grew on the mammoth steppe. The two-fingered tip of their trunk enabled them to pick up the short grasses. A frozen one-month-old calf called "Lyuba”, discovered near the River Yuribey in Siberia in 2007, still had food in its stomach. This included her mother’s dung, which, like modern elephants, the juveniles ate in order to inoculate their guts with microbes in preparation for digesting plants.
The woolly mammoth chewed its food by using its powerful jaw muscles to help grind its food. The ridges on its molar were resistant to wear. They may have used their tusks as shovels to clear snow from the ground and reach the vegetation buried below.
Ice Ages
The Pleistocene Ice Ages—one of a number of ice ages that have taken place throughout the Earth’s history—began around 2.6 million years ago. Since then, on at least four occasions, global temperatures plunged and great ice sheets spread southwards from the poles across much of Europe, Asia and North America.
These events are known as glacial periods and lasted for tens of thousands of years. In between, there were periods of warmer, even subtropical, climate, called interglacials. We may be living in an interglacial today.
The last glacial period of the Pleistocene Ice Ages, which is often known (incorrectly) simply as the “Ice Age”, took place between 126,000 and 11,500 years ago. It reached its peak during what scientists call the Last Glacial Maximum, when ice sheets started advancing 33,000 years ago and reached their maximum extent 26,500 years ago. During this time, because so much water that would normally circulate between the oceans and the atmosphere was frozen, or “locked up”, in the ice, sea levels across the globe fell dramatically. Many islands—and even the continents of Asia and North America—became linked by “land bridges”, tracts of dry land that were once covered by seas.
During the Last Glacial Maximum, the mammoth steppe, a vast, cold, dry grassland lying to the south of the ice sheets, stretched from Spain across Europe and Asia (as far south as China) and over the Beringia land bridge into Alaska and the Yukon.
The ice sheets started to retreat in the Northern Hemisphere around 19,000 years ago, reaching their current positions in the polar regions about 11,500 years ago. When the ice melted, sea levels began to rise, flooding the land bridges.
Recreating mammoths
The presence of soft tissue and DNA in the well-preserved remains of woolly mammoths has led some scientists to look into whether mammoths could be recreated—brought back from extinction. Several methods have been proposed. Cloning would involve replacing the nucleus of the egg cell of a female elephant with one from woolly mammoth tissue. The new cell would then be inserted back into a female elephant. The resulting calf would then have the genes of a woolly mammoth. However, most mammoths do have not enough usable DNA for this purpose.
The most likely method (but an extremely difficult one) is to recreate a complete set of woolly mammoth genes, then add them to those of an Asian elephant. If this process were ever to be successful, elephant-woolly mammoth hybrids (mixed species) could be created, and perhaps be kept at a “Pleistocene Park” wildlife reserve in Siberia.
Consultant: Chris Jarvis