Why is the "hairy monster" roaming the Eurasian continent "frozen" underground?

The mammoth-woolly rhinoceros group, which adapted to cold weather during the Late Pleistocene, was widely distributed in the high latitudes of the Northern Hemisphere [1]. As the most widespread mammal group on Earth, it was widely distributed and had a stable composition. Its main members included mammoths, woolly rhinoceros, bison, cave bears, brown bears, cave lions, moose, reindeer, saiga antelopes, and musk oxen (Figure 1). Many members of the mammoth-woolly rhinoceros group were frozen after death, leaving behind corpses that have not decayed for thousands of years. This has provided scientists with invaluable materials for exploring the biological characteristics of these extinct animals and their rise and fall history [2]. The same group of animals is also distributed in Northeast my country, where mammoths are the most widely distributed and common members of the mammoth-woolly rhinoceros group (Figure 2). The true mammoth is a true mammoth, also known as the woolly mammoth, characterized by thick hair that can be up to 8 cm thick and long incisors. The mysterious image of the true mammoth has always attracted the exploration of scientists and history enthusiasts. This article will take you into the world of true mammoths, revealing their living habits, the mystery of their extinction, and their relationship with modern elephants.

Figure 1. Main members of the mammoth fauna (A) (cited from Mol et al., 2004) and their distribution range during the Ice Age (B).

Figure 2. (Left) Fossils of members of the woolly mammoth-woolly rhinoceros fauna commonly seen in the Northeast Plain of my country, (Right) the frozen body of the mammoth "Lyuba" who was less than one year old.

1. The origin and evolution of woolly mammoths

The origin and evolution of the woolly mammoth, an ancient prehistoric giant, is full of mystery and challenges. As a member of the genus Mammuthus, the taxonomic status of the woolly mammoth has undergone many reassessments over the past few centuries. Their relationship with modern elephants once sparked heated debate in the academic community, but the progress of modern molecular biology has revealed a clearer picture for us. According to fossil records, the woolly mammoth (Mammuthus primigenius) is also known as the woolly mammoth. We now believe that the woolly mammoth originated in Africa and first appeared 3 million years ago. The subplanifrons (Mammuthus subplanifrons) is considered to be the direct ancestor of all mammoths in Eurasia. It later migrated to Eurasia and evolved into a new species. According to records of fossil bones in Europe, it evolved into the steppe mammoth (Mammuthus trogontheri) in the Middle Pleistocene, and became a fully evolved primitive mammoth about 700,000 years ago. It first appeared in Europe about 200,000 years ago. After the last ice age, the woolly mammoth spread to the high latitudes of the Northern Hemisphere, across Eurasia, and into North America. It was particularly widely distributed until 11kaBP, when the woolly mammoth disappeared from the entire Eurasian continent (except for island subspecies) [3-5].

Figure 3. Evolution and diffusion patterns of mammoths in Eurasia and North America

Scientists have been able to reconstruct the evolutionary tree of mammoths through careful study of fossil samples and in-depth analysis of ancient DNA. For example, DNA from molars of woolly mammoths discovered in Siberia in the 1970s revealed that the ancient ancestors of woolly mammoths had already begun to develop genetic traits that adapted to cold environments about 1 million years ago. These traits were optimized in woolly mammoths, enabling them to survive in extremely cold environments[6].

The origin and evolution of the woolly mammoth is a spectacular chapter in the history of life on Earth. Their adaptive characteristics not only allowed them to occupy a place in the Ice Age, but also provided us with valuable information on how organisms cope with environmental changes. At the same time, these studies also provide scientific basis and guidance for modern scientists to try to revive extinct species, such as mammoths, and open a new window for exploring biological genetics and cell biology. Although the woolly mammoth has disappeared in the long river of history, their legacy and stories will continue to inspire and lead us to explore the mysteries of life in depth.

2. Physiological characteristics and living environment of woolly mammoths

The true mammoth can reach a height of 3 to 3.7 meters and weigh up to 300 kilograms. It was a behemoth among land creatures at that time (Figure 4). Their huge size helps to slow down the loss of heat, making it more effective to maintain body temperature in cold climates. The hair of the true mammoth is one of its most notable features. They have a thick yellow-brown undercoat covering their skin, providing them with a natural barrier to keep warm. Under this undercoat, there is also a layer of fine hair, which plays an excellent role in insulation. In winter, the hair of the true mammoth will become thicker to cope with extremely low temperatures. In addition to hair, there is an extremely thick layer of fat under the skin of the true mammoth, which can be up to 10 cm thick, which not only helps to keep warm, but also stores a lot of energy to help them survive in the winter when food is scarce. This fat layer can form a hump on the back, making the true mammoth look a bit irregular, but this is one of their strategies to survive in cold environments.

Figure 4. (Left) Fossil skeleton of a woolly mammoth; (Right) Reconstructed image of a woolly mammoth

The woolly mammoth's signature feature is its pair of long, downward-curving tusks. These tusks were used not only for foraging, such as digging through the snow to find plants underground, but also as weapons to protect itself and its family. The tusks could reach 4 meters in length and weigh more than 100 kilograms, making them the largest teeth of all terrestrial mammals. Scientists speculate that the tusks may also help dissipate heat, offsetting the excess heat generated by males competing for mates. The woolly mammoths chose to live in the vast grassland tundra areas of Eurasia and North America, which were covered with ice and snow during the Ice Age, with extremely low temperatures and sparse vegetation. Their ears were relatively small and oval, which helped reduce heat loss. In addition, their wide feet helped them walk on ice-covered ground and reduced the possibility of sinking into the snow.

In such an environment, the physiological structure and behavior patterns of true mammoths reflect deep adaptation to the severe cold. They live in groups to resist the cold and the threat of predators. In the summer when food is abundant, they will accumulate a lot of nutrients to prepare for the winter. In winter, they will dig through the snow to find plants buried underneath, such as grass roots and moss, to survive.

3. Extinction of the woolly mammoth

The final extinction of the woolly mammoth is a fascinating chapter in Earth's long history. Although they were once widespread across Eurasia and North America, this once-invincible population disappeared without a trace in a short period of time, about 12,000 to 10,000 years ago. Scientists have proposed a variety of hypotheses to explain this phenomenon, including climate change, human hunting pressure, and the impact of disease.

Climate change is one of the main candidate factors for extinction. The rapid retreat of the last ice age led to the rapid expansion of tundra and grassland, which may have changed the food source and habitat of the woolly mammoths, making them unable to adapt to the new environmental conditions. In addition, climate change may have affected the growth of plants, reducing the variety and amount of plants available for the woolly mammoths to eat.

Human hunting may also be an important factor in the extinction of woolly mammoths. As humans transitioned from hunting and gathering to agricultural society, hunters' demand for large prey increased, which may have led to a sharp decline in the number of mammoths. Archaeologists have found a large number of woolly mammoth remains in Europe and North America, which have obvious signs of human hunting, providing evidence for this hypothesis.

The woolly mammoths lived and multiplied in Eurasia during the last ice age, MIS3. They migrated around 21-19 ka BP and survived only in northern Siberia and the western part of the central plains of European Russia. The reason for the reduction in the distribution range of the woolly mammoths during this period has not been found, and the woolly mammoths subsequently returned to Europe. Around 14.7-12.6 ka BP, the climate suddenly warmed, and the distribution range of the woolly mammoths in Eurasia shrank greatly, with a relatively small number. Around 12.6-11.5 ka BP, the cold climate struck again, and the distribution range of the woolly mammoths briefly spread to the eastern part of Eurasia (northeastern China). At 11.5 ka BP, the woolly mammoths disappeared from Eurasia. The exact age of the final extinction of the woolly mammoths has not been found on the Siberian continent. Only the woolly mammoths were found in the Siberian Islands at 10.7 ka, and the subspecies of the woolly mammoth, the Wrangel mammoth, lived on Wrangel Island. The extinction of woolly mammoths was probably caused by hunting by humans living at the same time. The reduction in the distribution range of woolly mammoths is believed to be mainly driven by climate. After about 200 ka BP, many temperature-adapted populations (late M. trogontherii) disappeared, leaving only the cold-adapted late Pleistocene woolly mammoths, which are more susceptible to climate warming and afforestation [4].

Modern research is still going on, trying to dig out more information about the woolly mammoth from fossils. Although the woolly mammoth has disappeared from the earth, their fossils and frozen remains provide us with valuable scientific information, helping us to understand the history and biodiversity of the earth more deeply. With the advancement of science and technology, some scientists have even proposed the idea of ​​"resurrecting" the woolly mammoth through gene editing technology. This is not only a scientific challenge, but also a profound reflection on life and nature. The story of the woolly mammoth is not only a history of biological evolution, but also a fable of the coexistence of humans and nature, reminding us to cherish every life and respect the laws of nature. While we pursue scientific and technological progress, we should also think about how to coexist harmoniously with other creatures on the earth.