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HomeScience & TechThe Buesching mastodon’s story is imprinted in his ivory

The Buesching mastodon’s story is imprinted in his ivory

There are worse fates than to end your days fighting for your very reason for being. And the Buesching mastodon’s reason for being was reproduction. The line connecting him with his ancestral past stretched back further not only than his elephantine brain could possibly have conceived, but further than any brain at all could have conceived until radiometric dating pinpointed the birth of planet Earth to a cosmic moment 4.54bn years ago.

Geologists argue about what is truly the first trace of life on Earth. But to say that living things have been around since about 4bn years ago will do as a nice, round estimate. Ever since then, the winnowing of natural selection has done its work. Only the strong have survived long enough to deliver their genes to the next generation. And boy, was he strong. Two tonnes of rippling muscle draped over a skeleton weighing the same, all powered by another four tonnes of visceral organs. And tusks. Two enormous tusks, each three metres long and weighing 40kg.

It is those tusks that best tell the Buesching mastodon’s tale. For, more than 13 millennia after his last, fateful encounter with another bull—one that proved stronger, or cleverer, or just luckier—they were discovered in 1998, along with the rest of his almost complete skeleton, in peat workings near Fort Wayne, Indiana. His biographers, Joshua Miller and Daniel Fisher, have been studying them ever since, and have just published their latest findings*.

Tusks are giant teeth. And teeth contain calcium phosphate. This is the material that strengthens them. But calcium is in the same column of the periodic table as strontium, a rarer element, so the two are chemically similar—so similar (and strontium so rare) that natural selection has never bothered to learn the difference. If the tusk-assembly process comes across a strontium atom, it incorporates it as though it were calcium, no harm done.

This harmless mistake gave Dr Miller and Dr Fisher much of what they needed to write their mastodon’s life story. Strontium comes in two isotopes (atoms of different weights). The ratio of these in plants of the sort which mastodons ate depends on their ratio in the underlying rocks. Like trees, tusks have annual growth layers. And the rocks of America’s Midwest are so well studied that their strontium ratios are well known. So the pair were able to trace with reasonable confidence whereabouts their mastodon was when a pertinent bit of a tusk was growing.

When he was there was given away by a second pair of isotopes—this time of oxygen atoms. Water molecules with the heavier version of oxygen in them are more reluctant to evaporate, so the ratio of the two isotopes in rainwater depends on the temperature, and therefore the season. And the oxygen from rainwater also ended up in mastodons via their fodder.

Where, then. And when. Reluctant to remove for isotopic analysis more that the bare minimum of material from their precious sample, Dr Miller and Dr Fisher concentrated on the years when the animal was between 11 and 16 years old, and between 31 and 34. But they had other information as well. Nutritional stress shows up in the appearance of the growth layers, as does damage caused by fighting other mastodons.

Previous studies suggest that male mastodons lived when young with their mothers, siblings, aunts and cousins, in matriarchal groups similar to those of modern-day elephants. Dr Miller and Dr Fisher did not bother to waste precious ivory confirming this. Instead, they started with the rebellious teenager.

The teenage Buesching mastodon, they found, was year by year extending his range in what are now the Midwestern states of Illinois, Indiana, Ohio and Michigan, but showed no seasonal preference for a particular place. He was also stressed by his adolescent years. At least, his tusks suggest he was not eating as well as he might have been.

At the height of his powers as a full-grown adult, though, all signs of stress are gone. Now he was migrating seasonally—returning in the early summer to a much smaller area near the centre of his range that seems to have served as a mating ground.

And he was pugnacious. Tusk damage suggests that from the age of 26 he was getting into regular scraps at this time of the year. These may reflect musth—periods of aggressive temperament experienced by modern male elephants. If they do, it suggests musth evolved a long time in the past. The last common ancestor of mastodons and modern proboscideans lived about 25m years ago.

Whatever the details, he met his match in the eighth year of these jousts. All of the procreative instincts drilled into his genes by the successful reproduction of his ancestors over the aeons—faint heart never won fair lady—culminated in the moment of his death. One of his opponent’s tusks punched through his right temporal fossa, a thin sheet of bone on the side of the skull, severing an artery. It left a hole almost 5cm across, visible to this day. That was the end of him. But previous seasons’ successes would probably have seen him get his genes into the next generation, so job done.

Nothing, though, lasts for ever—even the lines of creatures as mighty as mastodons. Palaeoanthropologists differ about when the peopling of the Americas began, but all recognise the rise of a culture called Clovis, with its suite of effective stone tools and weapons, particularly spearheads. That started shortly after the Buesching mastodon’s final, fatal fight.

Clovis weapons changed the rules of engagement between humans and the local wildlife. Mastodons, along with their proboscidean cousins the mammoths and a whole range of other large American mammals, from sabre-toothed cats to armour-plated glyptodonts, did not long survive contact with this supreme embodiment of the 4bn-year winnowing of the gene pool. All gone, their genetic lines cut off for ever. But not forgotten. At least, not while biographers like Dr Miller and Dr Fisher ply their trade.

*PNAS, Male mastodon landscape use changed with maturation (late Pleistocene, North America), J.H. Miller et al.

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