Clues to mysterious disappearance of North America’s large mammals 50,000 years ago found in ancient bone collagen

50,000 years ago megafauna ruled North America. Lumbering mammoths roamed the tundra, while the forests were home to towering mastodons, ferocious saber-toothed tigers, and huge wolves. Bison and exceptionally tall camels roamed the continent in herds, while giant beavers roamed its lakes and ponds. Huge ground sloths weighing over 1000 kg have been found in many areas east of the Rockies.

And then, sometime at the end of the last ice age, most of North America’s megafauna disappeared. How and why is still a matter of great controversy. Some scientists believe that the arrival of humans was the key. Maybe the animals were hunted and eaten, or maybe people just changed their habitats or competed for vital food sources.

But other scientists say climate change was to blame, as the Earth was melting after several thousand years of icy temperatures and the environment was changing faster than the megafauna could adapt. The disagreements between the two schools were fierce and the debates contentious.

Despite decades of study, this Ice Age mystery remains unsolved. Researchers simply don’t have enough evidence at this point to rule out one scenario or the other—or even the other explanations that have been proposed (eg, disease, comet impact, combination of factors). One reason is that many of the bones through which they monitor the presence of megafauna are fragmented and difficult to identify.

While some sites preserve megafaunal remains really well, at others the conditions were harsh on the animal bones, wearing them down into smaller fragments that are too altered to be identified. These degradation processes include exposure, abrasion, breakage, and biomolecular breakdown.

Such problems leave us with critical information about where individual megafaunal species were distributed, when exactly they disappeared, and how they responded to the arrival of humans or to environmental climatic changes in the late Pleistocene.

Application of modern technologies to old bones

New work, published in Frontiers in Mammal Science, decided to solve this information deficit. To do so, they turned their attention to the exceptional collections of the Smithsonian National Museum of Natural History in Washington, DC. The museum, which contains findings from numerous archaeological excavations carried out over the past hundred years, is an extraordinary reservoir of animal bones that are deeply relevant to the question of how North America’s megafauna became extinct.

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

Fortunately, new biomolecular methods of archaeological research have been developed in recent years. Rather than excavating new sites, archaeologists are increasingly turning their attention to the scientific laboratory, using new techniques to examine existing material.

One such new technique is called ZooMS – short for Zooarchaeology by Mass Spectrometry. The method relies on the fact that while most of its proteins break down quickly after the animal’s death, some, such as bone collagen, can be preserved for a long time. Because collagen proteins often differ in small, subtle ways between different taxonomic groups of animals and even within 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 tiny amounts of bone can be separated and analyzed on a mass spectrometer to make identifications of bone remains that traditional zooarchaeologists cannot.

Selection of archaeological material for study

The researchers decided to use this method to revisit the Smithsonian Museum’s archived material. Their study was a pilot that asked a key question: would the bones housed in the Smithsonian Museum preserve enough collagen for us to learn more about the fragmented bone material in its stores?

The answer was not obvious because many of the excavations took place decades ago. While the material has been stored in a state-of-the-art climate-controlled facility for the past decade, the early date of the excavation meant that modern standards were not necessarily applied to its handling, processing and storage. all phases.

The team examined bone material from five archaeological sites. All sites were dated to the late Pleistocene/early Holocene (about 13,000 to 10,000 calendar years before present) or earlier and were located in Colorado in the western United States. The first was excavated in 1934, the last in 1981.

Although some of the material from the sites was identifiable, much of it was highly fragmented and did not retain diagnostic characters that would allow zooarchaeological identification to species, genus, or even family. Some of the bone fragments looked very unpromising – they were bleached and weathered or rounded, suggesting they had been transported by water or sediment before being buried at the site.

Discovering superior biomolecular protection

What they found surprised them. Despite the high age of many collections, the unpromising appearance of much of the material, and the ancient origin of the bones themselves, ZooMS yielded excellent results. In fact, a remarkable 80% of the bones collected yielded enough collagen for ZooMS identification. 73% could be identified to genus level.

The taxa they identified using ZooMS included Bison, Mammuthus (the genus that includes mammoths), Camelidae (the family of camels), and possibly Mammut (the genus that includes mastodons). In some cases, they could only place specimens into broad taxonomic groups because many North American animals still lack ZooMS reference libraries. These databases, which are relatively well developed for Eurasia but not for other regions, are necessary to identify the spectra that a sample produces when run on a mass spectrometer.

Their findings have a major impact on museum collections. The material the researchers looked at is in every way a poor cousin to the glamorous material on display in natural history museums.

On the face of it, these highly fragmentary, small and undiagnosed animal bones are uninspiring and superficially uninformative. But like other biomolecular tools, ZooMS is uncovering rich information preserved in neglected specimens that have not attracted the attention of researchers or visitors for decades.

The results also highlight the potential of such collections to resolve ongoing debates about exactly when, where and how megafauna became extinct. By making the fragmented bone material that makes up much of the megafauna record available for analysis, ZooMS has the potential to help provide a wealth of new research data to address long-standing questions about megafauna extinction. ZooMS offers a relatively easy, fast and inexpensive way to extract new information from long-excavated sites.

Their research also highlights the importance of preserving archaeological collections. When researchers and institutions are strapped for funding, archaeological artifacts and bones that are not glamorous or have no obvious immediate benefit may be neglected or even discarded. It is very important that museums have sufficient financial resources to care for archaeological remains and store them in the long term.

As their analysis shows, such old material can find new life in unexpected ways—in this case, allowing us to use tiny bone fragments to help us get closer to solving the mystery of why some of the largest animals ever to appear on Earth disappeared from the landscape. of ancient North America.