Ghosts of North America

In North America, we live surrounded by the ghosts of mastodons, saber-toothed cats, ground sloths, bear-sized beaver, and other wild giants.  These creatures died out 13,000 years ago, at the close of the last Ice Age, but new research continues to reveal fascinating details of their lives and to hint at the reasons for their mass extinction.

Fossil finds make it clear that mastodons once browsed in Manhattan, and mammoths stomped along Wilshire Boulevard in Los Angeles.  Lions—the same species still living in Africa, though the American version was about 25 percent larger—roamed the continent.

I’ve had a passion for these great beasts since I was a kid growing up in Chicago.  The sight of a mounted mastodon skeleton thrilled me: these monsters had once ambled through my own neighborhood!  I liked to imagine them rising up from beneath the pavement and rampaging down Lake Shore Drive.  As I learned more about them, I became even more enthralled.  Like living elephants, American mammoths and mastodons were social creatures, with strong family ties.

To help other people relate to these lost giants on a personal level, I tell the story of a young mother who lived in Michigan 13,000 years ago.  She had a tough life, losing 3 of her babies before they reached the age of one year.  When she died, members of an enemy tribe came along, found her body, and ate parts of it.  Once I’ve got my audience envisioning this harsh scenario, I reveal the kicker.

This young mother was not human.  She was a mastodon, one of the very last of her kind.  (We know her life story in such detail because paleontologist Dan Fisher of the University of Michigan read it in the growth lines of her tusk.)  The enemies who ate the meat from her body were some of America’s earliest human settlers, and they may have helped drive the mastodon and other native giants—known collectively as the megafauna—to extinction.

Detailed analysis of the growth rings found in mastodon tusks from the last 2,000 years of the Ice Age show that mastodons began to mate at progressively younger ages.  That trend is often a sign that a group of animals is experiencing intense hunting pressure.  Breeding earlier in life gives them more of a chance to reproduce before they are hunted down.  The last mastodons lived at a time of rapid climate change.  As glaciers receded, temperatures climbed and the environment became drier.  America’s native elephants would have been trapped at oases near water sources, where they became relatively easy targets for Stone Age hunters.

Fossil remains of mammoths and mastodons hunted and killed by people have been found scattered from Arizona to Maine, always at a water source.  The megafauna had survived the many previous warm spells that punctuated the Ice Age by roaming over great distances in search of forage.  The arrival of human hunters may have made that more difficult.

Modern megafauna—including elephants, rhinos, lions, wolves and grizzly bears–live in small islands of habitat surrounded by cities, ranches and roads.  They face a warming trend more rapid and intense than any in the history of mammalian evolution.  And they live among an unprecedented number of humans, who continue to hunt the few wild giants left standing.  What these threatened beasts need most is room to move: corridors of habitat that will allow them to navigate through a rapidly changing world dominated by people.

That understanding has inspired a movement toward international wildlife parks in Africa and the Americas, an effort to give living megafauna the space they need to adapt and survive.

Sharon Levy