In the spring of 2007, Siberian reindeer herder Yuri Khudi and his family excited researchers all over the world with their inadvertent discovery. They’d stumbled upon the carcass of a baby mammoth, exhumed by nature after 40,000 years of being frozen in permafrost. With the exception of some missing hair and toenails, she was almost entirely intact.
Little Lyuba, gratefully named by researchers in honor of Khudi’s wife, is the most well-preserved mammoth specimen ever found. This is incredibly exciting for researchers, as Lyuba presents opportunities we’ve never had to test our theories on something so complete. These theories include not only how mammoths and their close relatives, mastodons, lived, but what their prehistoric climate was like, and even why they went extinct.
We’ve based our theories on studies of what we do have—their elephant descendants, less well-preserved prehistoric carcasses, and a wealth of mammoth and mastodon bones, teeth and tusks. Tusks have proven to be an especially rich resource for elucidating detailed data about diet, health, life cycles—time of weaning, maturity, and reproduction—and environment. Believe it or not, all of this information is encoded in a tusk’s structure and composition.
Of Tusks and Teeth
Mammoth tusks are really just enlarged incisor teeth that, like those of their modern elephant relatives, continue to grow throughout their lives. As they grow, they form new layers of dentin, a calcified substance that is the primary component of all teeth (even your own).
If you slice open a tusk, these layers are visible as rings, like the rings of a tree, that provide a record of growth in yearly, weekly, and even daily increments. We study both the number of rings as well as their individual thickness. When a mammoth is growing quickly, indicating that it has plenty to eat and is healthy, the rings that develop at weekly intervals will be thicker than those of an animal growing more slowly.
Knowing this, we can observe some pretty interesting aspects of a mammoth’s life cycle in its tusks. For example, we’ve deduced from a number of studies that mammoth females lived separately from adult males. When a male mammoth reaches maturation, he is kicked out of the matriarchal tribe and forced to live on his own while looking for females with whom to mate. This can be observed in the tusk-growth patterns, as right around the age of maturity, the weekly interval rings suddenly become much thinner, indicating the mammoth is getting less to eat while he learns to fend for himself.
We also use isotope analysis to gather information from growth rings. Mammoths are herbivores, meaning that they eat primarily plants, and some of the carbon from these plants is incorporated in their tusks as they grow. Proportions of different isotopic forms of carbon in tusk rings can tell us what kinds of plants the mammoth was eating.
By isotopic forms, I mean different forms of the same element. As you may remember, an atom’s nucleus is composed of two kinds of particles—protons and neutrons. To be considered the same element, atoms must have the same number of protons. For example, all carbon atoms have six protons in their nucleus.
However, some atoms of the same element have more or less neutrons than others, and these variant forms are called isotopes. There are two naturally abundant stable isotopes of carbon, carbon-12 and carbon-13. Stable means that these isotopes do not decay over time. Carbon-14 is unstable, or radioactive, and is the isotope used in radiocarbon dating.
Different types of plants are known to have different proportions, or ratios, of carbon-13, which is less abundant, to carbon-12, which is more abundant. Because this proportion is preserved in tusks, we can measure the ratio of carbon-13 to carbon-12 from growth ring to growth ring to determine what kinds of plants a mammoth was eating from season to season and from year to year. And, since plant types with different ratios tend to grow in different conditions (temperature, precipitation levels, etc.) we can also infer some details about the climate in which the mammoth was living.
While these studies have told us a great deal about mammoths and mastodons, Lyuba’s discovery presents even more exciting possibilities. One is that she provides us a rare opportunity to confirm what we’ve inferred from tusks through studying other aspects of her well-preserved anatomy. For example, according to Lyuba’s tusks, she was well-fed and healthy right up to the moment of her untimely death. The rest of her body told us the same story though an ample amount of fat around her frame and a stomach full of milk, presumably her mother’s, along with other materials.
Clues to the Extinction Mystery
Studying mammoths via tusks and confirming these findings through well-preserved specimens like Lyuba give us clues as to why most mammoths went extinct some ten thousand years ago. There are several theories as to why this extinction occurred. One suspected culprit is climate change, which some researchers theorize restricted or reduced the mammoth’s food supply to a dire degree. Other scientists posit that early humans are to blame, and that they hunted mammoths to the point of extinction.
So how can we determine which of these two scenarios is more likely? Fortunately, these two options would produce opposite effects in mammoths physiologically. Take the first theory—if climate change affected the food supply so severely, the impacts on the mammoth population leading up to extinction—poor diet, high physical stress, slow growth patterns and later onset of maturity—would be easily observable in tusks.
Evidence for the second theory would be equally observable. As humans hunted and killed more and more mammoths, there would be a smaller population with which to compete for food supplies. Plentiful food would then foster faster growth and earlier maturity for those who remained.
While researchers still disagree about which theory is correct, and many more studies across different populations of mammoth and mastodons will be required to know for sure, the data we do have are consistent with the second theory—that mammoths and mastodons were over-hunted. Studies of their tusks show healthy animals and higher growth rates leading right up to extinction.
Lyuba—Shedding Light on Our Past, Present and Future
Our studies of prehistoric mammoths and mastodons provide more than just a window into our past. Ecologists studying modern-day elephants can use our methods of analyzing tusks to monitor current populations in different areas around the world. And, learning about when and why mammoths and mastodons went extinct can help ecologists determine critical points for conserving and stabilizing endangered elephant groups.
A perhaps lesser-known benefit of studying prehistoric populations is the knowledge we gather about the environments in which they lived. As we discussed briefly above, isotope analysis provides information about an animal’s diet and nutritional stressors. Likewise, proportions of oxygen isotopes recorded in their tusks tell us about aspects of the climate in which they lived.
For example, measuring the ratio of oxygen-18 to oxygen-16 from ring to ring tells us how the temperature and precipitation levels to which the mammoths were exposed changed over time. Since each tusk can provide between 30 and 50 years of data, they serve as natural high-tech recorders of our world’s climate history, and researchers can use their output to test computer-generated models of climate change. By using these models and other data, such as prehistoric temperature, carbon dioxide, and methane levels recorded in the geological record and ancient samples of glaciers derived from ice cores, researchers can observe an accurate record of our past climate. They can then use this information to make better projections of future change and its implications.
As scientists from almost any discipline will tell you, studying our past is an integral part of providing a better future. Lyuba is just one illustration of how a well-preserved glimpse into prehistoric times can tell many stories, from simply satisfying curiosities about the great animals that used to roam our Earth, to learning lessons that inform how to better protect those that still do.
You can learn more about Lyuba and her ancestors at the Field’s new exhibit, Mammoths and Mastodons: Titans of the Ice Age, which opened on March 5th and runs through September. Lyuba herself will be on display as part of a broad exploration of the evolutionary history of mammoths and mastodons, their environment, how they interacted with early humans, and how studying their lives and extinction can inform conservation today. For more information, visit the Field’s website.