Novel technique uncovers clues to disappearance of North America's large mammals 50,000 years ago

50,000 years ago, North America was ruled by megafauna. Lumbering mammoths roamed the tundra, while forests were home to towering mastodons, fierce saber-toothed tigers and enormous wolves. Bison and extraordinarily tall camels moved in herds across the continent, while giant beavers plied its lakes and ponds. Immense ground sloths weighing over 1,000 kg were found across many regions east of the Rocky Mountains.

And then, sometime at the end of the Last Ice Age, most of North America's megafauna disappeared. How and why remains hotly contested. Some researchers believe the arrival of humans was pivotal. Maybe the animals were hunted and eaten, or maybe humans just altered their habitats or competed for vital food sources.

But other researchers contend that climate change was to blame, as the Earth thawed after several thousand years of glacial temperatures, changing environments faster than megafauna could adapt. Disagreement between these two schools has been fierce and debates contentious.

Despite decades of study, this Ice Age mystery remains unsolved. Researchers simply don't have sufficient evidence at this point to rule out one scenario or the other—or indeed other explanations that have been proposed (eg disease, an impact event from a comet, a combination of factors). One of the reasons is that many of the bones through which they track the presence of megafauna are fragmented and difficult to identify.

While some sites preserve megafaunal remains really well, conditions at others have been tough on the animal bones, wearing them down into smaller fragments that are too altered to identify. These decay processes include exposure, abrasion, breakage, and biomolecular decay.

Such problems leave us lacking critical information about where particular megafaunal species were distributed, exactly when they disappeared, and how they responded to the arrival of humans or the climatic alteration of environments in the Late Pleistocene.

Applying modern technology to old bones

A new work, published in Frontiers in Mammal Science, set out to address this information deficit. To do so, they have turned their attention to the exceptional collections of the Smithsonian National Museum of Natural History in Washington, DC. Housing the findings of numerous archaeological excavations conducted over the past hundred years, the Museum is an extraordinary reservoir of animal bones that are deeply relevant to the question of how North America's megafauna went extinct.

Yet many of these remains are heavily fragmented and unidentifiable, meaning their ability to shed light on this question has, at least up until now, been limited.

Fortunately, recent years have seen the development of new biomolecular methods of archaeological exploration. Rather than heading out to excavate new sites, archaeologists are increasingly turning their attention to the scientific laboratory, using new techniques to probe existing material.

One such novel technique is called ZooMS—short for Zooarchaeology by Mass Spectrometry. The method relies on the fact that while most of its proteins degrade quickly after an animal dies, some, like bone collagen, can preserve over long time periods. Since collagen proteins frequently differ in small, subtle ways between different taxonomic groups of animals, and even individual species, collagen sequences can provide a kind of molecular barcode to help identify bone fragments that are otherwise unidentifiable.

So, collagen protein segments extracted from minute quantities of bone can be separated and analyzed on a mass spectrometer to perform the identifications of remnant bones that traditional zooarchaeologists cannot.