In 1998, outside of Fort Wayne, Indiana, a hydraulic excavator at Buesching’s Peat Moss & Mulch stripped back a layer of peat and struck bone in the underlying marl. Bone is the right word: This bone belonged to a mastodon, and mastodons are still fresh bodies in the dirt, not petrified fossils entombed in the rock. Although they might be popularly imagined living way back with the dinosaurs, the Ice Age megafauna went extinct only moments ago, in staggered waves over human history. The last mammoth, for instance, died after the first pyramids were built. Yet we know little of the lives of these animals with which we shared the planet for hundreds of thousands of years.
The mastodon pulled from the Indiana muck now lives in the state museum, looming over visitors, a stand-in for his entire species and epoch. Such relics rarely get to speak of their own lives. That this animal, nicknamed Fred, might have had his own biography is betrayed only by the ominous hole on the underside of his skull. “It got a tusk tip into the cheek,” says the University of Michigan paleontologist Daniel Fisher, grimly signaling to the roof of his mouth. That is, the mastodon was probably killed by another one. But inscribed in Fred’s own bowed tusks scientists have found a “ticker-tape record of his entire life.” Written in bone are 13,200-year-old memories of a mastodon living in the twilight days of his species. He migrated across the Midwest with the seasons, living in a world about to change forever.
This is Fred’s story, as best as Fisher and his colleagues can tell.
By all indications, Fred was a happy young mastodon, his welfare secured by a doting mother and the watchful aegis of his aunts. The planet had been emerging from the depths of the last ice age for thousands of years, and where there were once ice sheets, chalky-blue glacial lakes, and barren plains of gravel carved by braided rivers of meltwater there was now only the memory of the moraines that the ice sheets had left behind. The taiga forest trailed the ice, and then the deciduous trees moved in during this age of climate change. But mastodons don’t live on millennial timescales, and all Fred knew was that he was well cared for by his herd, and that he had plenty to eat in the forest. Walnut, hickory, oak, maple, and black and white spruce trees lined the great marshes of the Midwest. Fred picked from lakeside sedges beside stag moose, camels, and giant beavers as the matriarch kept watch for dire wolves. His tusks grew vigorously in these youthful salad days.
“There’s a time when they’re young and life is wonderful,” Fisher told me. “Particularly if they have the good luck to be the calf of the matriarch, every effort is made to see that they get good food, starting with extra milk.” Because of the cruel math of mastodon reproduction, male calves would have been nursed longer than females. Although females were likely to have mating success in their lives, competition for mates among the males was a winner-take-all blood sport in which male mastodons would likely sire many offspring or none at all. Preparation for the sorts of battles that would ultimately take Fred’s life, then, began in the nursery.
This was Fred’s story until age 12. His tusks grew robustly each year until—well, they suddenly didn’t. In adolescence, Fred likely started acting like a jerk. Fred had to go.
“Sometimes they get way too rowdy, and they’re trying to sort of ‘practice mate’ with their cousins and siblings—not that they would get anywhere—but … they don’t know when it should stop,” Fisher said of the similar adolescent angst seen in modern elephants. “So they will actually get kicked out of the herd. All of a sudden you see a year where the tusk grows half of what it did before. You think the sky must have fallen. What happened to these guys?”
At this point, isotopes in Fred’s tusks began recording a mastodon bildungsroman of sorts, as the animal struggled to come to terms with onrushing adulthood.
To unravel this coming-of-age story, Fisher and his colleagues, led by Joshua Miller at the University of Cincinnati, targeted two of the subtle signals recorded in the animal’s tusks, which grew layer by layer from the base outward, over the course of his life and which were made from the world around him.
We move through life picking up the signatures of the places we visit, unknowingly sampling from a palette of isotopes distilled by mountain ranges, by the vastness of the continent, and by the changing of the seasons. And because we are what we eat and drink, we reflect this porous exchange with the geosphere in our tissues and in our bones. Spend time far from the ocean, drinking water filtered by the long, evaporative journey overland, and your hair will know. Pluck the feather from a peregrine falcon or the barnacle from a humpback, read its isotopes, and you will learn of lengthy migrations over land and sea, recorded in years past. Even the heights of soaring mountain ranges, long since eroded to nothing, are preserved in the isotopes where they once stood, the measurable lightness of the ancient water that once capped their peaks in snow persisting in the rocks left behind.
Amazingly, the shifting signature of isotopes in Fred’s tusks provides a rough map of the animal’s movements thousands of years ago. Earth’s continents are mosaics of old granite magma chambers, frozen lakes of basalt, ancient limestone seafloors, the coals of bygone swamps, the sandstones of erstwhile deserts and beaches, and so on—all lathed by erosion, each lending its own isotopic flavor to the local environment. This isotopic landscape has been mapped in detail by geochemists, so when Fred sampled from this surface geology over the course of his lifetime, drinking from lakes or patiently gnawing at spruce twigs, the strontium in his tusks recorded an approximate geochemical GPS of his wanderings.
What this signal reveals is a home range that hardly budged in Fred’s early adolescence, while the hale and hearty growth rates of childhood dramatically fell off. Kicked out of the herd but unprepared to strike out on his own, Fred was likely extraordinarily stressed. The crisis is familiar to those who study the mastodons’ modern relatives. “The elephant will just stand maybe a mile away from the herd,” Fisher said. ”They know they can’t come close or the matriarch will shoo them away. They can’t have what they want, but they don’t know how to strike out for themselves yet. So they just stand and bawl and bellow at the margin of the matriarchal herd until finally they realize, There’s nothing for me here.”
That is, until they finally accept that childhood is over, and it’s time to go. This was a painful time—a time of privation.
“Once they’ve left the herd, it takes them a few years to learn how to feed themselves, and they don’t get back on their former trajectory until two to three years later,” Fisher said.
Only at this point does the strontium in Fred’s tusks indicate a growing range, as he set out from home, moving hundreds of miles over the landscape, learning to live on his own.
Migrating across the Midwest, his range potentially reaching from Illinois to Ohio, Fred plucked water lilies from the great marshes in the early autumn. He spent winter nights trudging through the fresh snowfall in moonlit clearings. Perhaps he thought back to his herd in the quieter moments. He gently wrapped his trunk around maple leaves and stripped spruce tips and buds from branches in the early spring. But this was a dangerous time as well: Males on their own are more vulnerable to accidental death than females, and if Fred had fallen into the muck, his aunts would not have been there to help pull him out. Nevertheless, after years of successful independent living, his growing confidence marked by a range that came to span more than 100 miles, Fred would pick up a new obsession: visiting northern Indiana at the same time each year. In the early summer, for at least the last eight years of his life, he would return here for explosions of mastodon-on-mastodon violence.
“Again and again and again every year—slam, slam—always at the same time of year, and always at the same season,” Fisher said, “which ultimately became the season of death.”
This cycle of violence was revealed by a second signal in Fred’s tusks, encoded in oxygen isotopes, which tracked the steady sawtooth tick of the seasons passing by and provided a kind of calendar kept in dentin. (Water with lighter oxygen would evaporate and precipitate in the brutally cold Pleistocene winters; heavier oxygen in the tusks, meanwhile, signaled the return of the ancient summer.) Combined with the isotopic record of Fred’s location, one that reveals regular migrations to northern Indiana near the end of his life, and the trauma recorded in annual scars in his tusks, these signals indicate to Miller that Fred’s dangerous early-summer pilgrimages were made in search of mates.
“Towards his death, when he is big enough and strong enough and hormonally enriched enough, he’s going through these annual cycles where he’s finding this region he’s only going to in the summer, and that includes the place where he’s found at death,” Miller told me. “It’s an annual migration to what we think are the mating grounds.”
Given mastodons’ remarkably long gestation times of about 22 months, and the extreme seasonal climate of the late Pleistocene, reproduction had to be exceptionally well timed so that their offspring could be born at the right time of year to maximize survival. This had the effect of concentrating competition over mates into an extraordinarily intense window. And so, each year Fred would return to the mastodon colosseum of greater Fort Wayne for incredibly violent rounds of combat.
“I have to say, it’s an almost shocking part of their biology,” Fisher said. “Elephants do do this to an extent, but I think mastodons did it even more than elephants. Elephant bones by comparison are gracile, slender—they’re like twigs compared to mastodons. We have evidence of mastodons just beating each other apart.”
The fact that Fred survived as many years as he did suggests that, until he met his grisly end, he fought well and likely found mating success, Fisher said. But evolution doesn’t make allowance for graceful exits. And so, Fred the mastodon was kicked out of his herd at age 12, roamed the Midwest, and was gored and died at 34, about 13,200 years ago.
This was one of the last of the elephant kin in North America. Fred’s species had millions of years in its rearview and mere millennia until extinction. He had lived the kind of boisterous, peripatetic, and ultimately tragic life that was perhaps typical of a venerable lineage that had survived wild climate swings, hundred-millennia-long planetary winters paced by the sinuous changes of northern sunlight, and the tug of celestial bodies. But where the planet had rocketed out of ice ages before and the megafauna had kept up, now an unprecedented actor stepped on the landscape.
“If you look at past deglaciations, some of which were even larger in magnitude, you don’t see extinctions,” the University of Nebraska at Lincoln biologist Kate Lyons told me. “Mammals were able to track their climate with no problem. There’s nothing different about this time, other than the arrival of humans.”
Though he was killed by another mastodon, Fred’s body bears witness to this growing presence of humans. He didn’t merely fall into the bog that ultimately preserved him for posterity; he was packaged for the future, his carcass carefully stashed in the mire, the meat carved off his bones, his tusks lovingly laid side by side. As the ice retreated, as it had many times before, the mastodons would fall away, and the humans who buried them would inherit the Holocene. Our own populations were swelling, and megafauna extinctions that had already hit Eurasia, Australia, and even Africa in the tens of millennia before were now sweeping the Americas.
“If you look at the selectivity of the extinctions at the end of the Pleistocene, what you see is that every time Homo sapiens arrive in a new landmass, the average body size of mammals there drops, usually by an order of magnitude or more,” Lyons said. “Going into an area and killing large-bodied mammals and driving them to extinction actually seems to be a signature of our species.”
In North America, where the extinctions that took the mastodons struck during a broader, millennia-long period of deglaciation, this background climate stress—which had proved survivable many times without humans on the landscape—suddenly became lethal. In our own time, as the climate is changing with a rapidity almost unknown in the geologic record, it’s an open question whether life could keep up without us in the way—much less with the patchwork of human infrastructure and farmland that now carpets the continents.
“We’re changing climate as much in 100 years as it changed over a couple thousand years over the past deglaciations. But to me the bigger problem is actually the barriers to dispersal that we put up,” Lyons said. “At least some elephant populations we know … will migrate thousands of kilometers. But for many of them, they’re essentially fenced into these game preserves. And there’s a lot of human conflicts when they get out.”
For this reason, Joshua Miller, Fisher’s colleague, calls animal migration of the sort revealed in Fred’s isotopes perhaps “the most endangered behavioral type” on our modern planet. He plans to put his forensic tools to work not only in deciphering the ranges of extinct animals but on elephant tusks going back centuries to reconstruct what remains an unknown baseline for the animals, even in historical times.
“We really have very little understanding of their requirements for landscape use,” he said. “What does an elephant really need to be happy?”
After the humans arrived, Fred stayed in his lightless bog for millennia as the land was worked above, the forests shaped by fire and the fields sowed with corn, beans, and squash. Then, in the moments before he was dug up, disease swept the continent, and guns followed. Where mastodons once battled, humans now slaughtered one another. The crops were burned, the great marshes of Indiana were drained, and many of the people were sent on a Trail of Death. In the centuries since, the forests and marshes have mostly been replaced by a checkerboard of soybeans and corn. Coal made from strange jungles that grew hundreds of millions of years earlier was pulled up from deep under the Midwest and ignited. Now the seaside dunes of northern Indiana, at the edge of the great glacial lakes, breathe fire from iron bellows, and the future of all elephants on Earth is threatened by the same processes that transformed this world in a matter of centuries. But when it’s over, this story will still be written in bone.
from Hacker News https://ift.tt/mtwedrP
No comments:
Post a Comment
Note: Only a member of this blog may post a comment.