Skeletal remains found on the ICC campus tell an ancient story.
On a cold, windy day about 18,000 years ago, an adult male mammoth lay down for the final time and died on the eastern bluff of a major river valley near what is known today as Peoria, Illinois. The climate in which he had lived was slowly warming. Glaciers that had covered northernmost Illinois with a thick sheet of ice for thousands of years were finally retreating, but Illinois was still a windy, cold place. It is likely that one of the mammoth’s last views was of the magnificent valley to his west, filled with shimmering water, ice and snow, and backed by the far western bluff of the river.
We can’t know how he died, but we can be reasonably certain that he was not killed by human hunters. Most evidence suggests that humans would not appear in his part of the world for another 3,000 to 4,000 years. Perhaps he caught a fatal disease or sustained a wound that did not heal properly. As he became sicker, he may have become easy prey for a saber-toothed cat, an American lion or a pack of dire wolves.
Eighteen thousand years later, a backhoe operator digging a trench on the campus of Illinois Central College in East Peoria discovered his skeletal remains. Most of his skeleton was gone by that time. Immediately after his passing, his remains would have been scavenged by birds, mammals, and flesh-eating insects. Undoubtedly, some of his bones were carried away by predators. What remained was covered by sand and soil, and by wind-blown glacial dust called loess. The soil covering his skeleton etched the softer bones away, leaving only the hardest parts to be discovered millennia later.
How can we know such details about an event that happened long before there were human witnesses to observe it? If all that remains are two molars and part of a tusk, how can we conclude the mammoth was a “he,” approximately 50 years old? How do we know what the environment he expired in was like, and how can we confidently make guesses about his behavior when he died?
We know for certain that a mammoth died on land that would become the campus of Illinois Central College. We know the remains were covered by soil that can be dated to about 18,000 years ago. From the pollen grains deposited around him, we know something about the plants that grew in the vicinity and the climate when he died. The rest we can deduce by scientific reasoning, based on evidence uncovered by the scientific method. What follows is how we can deduce what happened on that distant day, 18,000 years ago.
DNA Provides Context
The molecule of life, found in almost all living cells, is called deoxyribonucleic acid, or DNA, which contains the code that gives each species on Earth its distinctive characteristics. Today, we have sophisticated machinery that has completely read (or “sequenced”) all of the DNA contained in the cells of human beings. We are now moving on to sequence more species, including modern-day elephants, fossil mammoths, and their ancient “cousins,” the fossil mastodons.
We can use DNA sequences to create an evolutionary tree. Species that are closely related have few differences in their DNA, while those more distantly related have a greater number of differences. By comparing the DNA of mammoths, mastodons and modern elephants, we can build a tree of relationships that shows a surprising result. The DNA of extinct mammoths and of Asian elephants are extremely similar, indicating they are very closely related. African elephants are more distant, and mastodons are the most distant of all.
Molars Tell Our Mammoth’s Age
Mastodons, which were living in Illinois at the same time as mammoths, were a much more ancient line of elephants that had evolved in tree-filled environments. Mastodon molar teeth were very different-looking teeth, with a shape indicating they ate leafy vegetation rather than grasses. The chewing part of the tooth had two rows of big “cusps,” or bumps, which were ideal for crushing leaves.
Modern elephants have very different molar teeth, with multiple, looped ridges on their chewing surfaces, as did mammoths. This type of tooth is superbly adapted for grinding grass. Grass is a very abrasive food, and teeth wear down quickly in any grass-eating animal. Because of this, modern elephants have a succession of molar teeth that appear throughout their lives. A baby African elephant gets its first small molar at the age of two or three. This tooth is ground down quickly and replaced by a succession of ever-larger molars until the age of 40 to 50, when the last tooth in the series pushes forward in the jaw. This tooth is eventually worn down as well, after which the elephant can no longer chew and eventually starves to death. We know that mammoths were similar.
The ICC mammoth had molars of a size and shape that would have first appeared in a 45-to-50 year-old mammoth—the final set of molar teeth he would have had. However, the teeth are only moderately worn down. Thus, we can be quite sure that he was about 50 years old when he died, and certainly did not starve to death because of worn-down teeth or an inability to chew.
The Tusk Yields Clues on Gender
How do we know the ICC mammoth was a “he”? Here, we must be a bit more speculative. Although parts of the mammoth skeleton would tell us its gender with certainty, these parts—the pelvis, for example—have been lost. However, we know male mammoths had tusks that were longer, more sharply curved, and much wider than females. Mammoth tusks from males had diameters measuring well above 10 centimeters and—in the largest males—up to 20 centimeters in diameter. Tusks from fully-grown female mammoths consistently measure less than nine centimeters across.
The ICC mammoth’s tusk is broken and eroded, and it’s missing most of its outer enamel casing, but a careful examination shows the tusk is at least 14.5 centimeters in cross section. The ICC mammoth has a tusk diameter well within the range for male mammoths and well above the female upper limit. Thus, the evidence strongly supports that the ICC mammoth was a full-sized, mature male of about 50 years of age.
Behavior Allows Us to Finish the Story
We know the behavior of Asian elephants, which are closely related to mammoths, and of African elephants, which share ancestors with them. It’s reasonable to assume that any behavior common to both living species was probably also present in mammoths.
If the ICC mammoth was in fact a “he,” we can be fairly certain that he was born into a herd of closely-related female mammoths, part of a group of a few small “boys” within the larger family. Young males are tolerated by modern elephant clans only up to the age of 15, after which they are ejected for good. His mother and her female relatives would have shared responsibility for the care of the young and looked out for the welfare of the entire herd. As he grew up, he would have learned the subsonic sounds used by mammoths to communicate with one another. These vocalizations probably could be heard not only by his own group, but by mammoths as distant as several miles away.
Recently-banished young male elephants sometimes form groups of two to three, but eventually, older males become solitary wanderers. Full-sized males have little to fear from predators and often live on their own for decades, interacting with females only during the mating season. Our ICC mammoth, if male, would have lived such a life. He likely would have died alone from disease or predation in his early 50s. He lived a long, full life and when it finally ended, it is possible that other mammoths who found his remains lingered over his body, seemingly contemplating his passing. Both species of modern elephants frequently exhibit similar behavior today.
Mastodons and Mammoths Disappear
Mammoths and mastodons became extinct about 11,000 years ago. Many other mammals went extinct in North America about the same time, including saber-toothed cats, North American camels, the short-faced bear, the American lion and muskoxen. The prairie soils of central Illinois contain a rich fossil record of life—a record that was significantly diminished after these wide-scale extinctions.
Illinois Central College announced recently that it will soon begin construction of a new “sustainability” center classroom building near the site where the ICC mammoth was found. It’s possible that fossilized bones of mammoths, mastodons, giant ground sloths, saber-toothed tigers, dire wolves and other extinct creatures may be found as the earth is turned on the new construction site. If so, a very eager ICC faculty team of scientists is ready and able to examine what the site reveals. iBi
Tom Griffiths is a biology professor at Illinois Central College.
Thank you for this fascinating article, which has inspired me to learn more about these sadly extinct creatures. I never knew so much could be deduced from so little remains, quite ingenious.
Since African elephants are thought to now comprise two species (http://www.nature.com/news/2010/101221/full/news.2010.691.html), I am curious how their molar teeth might differ.
I also wonder how similar the African elephant molar tooth is to the Mammoth, Asian, and Mastadon teeth pictured, since African and Asian elephants are considered to be separate genus and species (though there is a documented case of African and Asian elephants interbreeding in 1978 described at http://www.hybridelephant.com/motty.html).