Clues to the mysterious disappearance of large mammals from North America 50,000 years ago have been discovered in ancient bone collagen

50,000 years ago, North America was ruled by megafauna. Lumbering mammoths roamed the tundra, while the forests were home to towering mastodons, ferocious saber-toothed tigers, and enormous wolves. Extraordinarily large bison and camels moved in herds across the continent, while giant beavers roamed its lakes and ponds. Huge ground sloths weighing more than 1,000 kg have been found in many areas east of the Rocky Mountains.

And then, at the end of the last ice age, most of North America’s megafauna disappeared. How and why remain very controversial. Some researchers believe the arrival of humans was crucial. Perhaps the animals were hunted and eaten, or perhaps humans simply altered their habitats or competed for vital food sources.

But other researchers say climate change was to blame, as Earth thawed after several thousand years of glacial temperatures, changing environments faster than megafauna could adapt. The disagreements between these two schools were fierce and the debates controversial.

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

While some sites preserve megafauna remains very well, at others conditions have been harsh on animal bones, reducing them to smaller fragments too altered to identify. These disintegration processes include exposure, abrasion, rupture, and biomolecular degradation.

Such problems leave us without crucial information about where certain megafauna species were distributed, when exactly they went extinct, and how they responded to the arrival of humans or climatic alteration of environments in the Late Pleistocene.

Applying modern technology to old bones

A new work, published in Frontiers of mammal science, has undertaken to remedy this information gap. To do this, they turned to the exceptional collections of the Smithsonian National Museum of Natural History in Washington, DC. Home to findings from numerous archaeological digs conducted over the past hundred years, the Museum is an extraordinary repository of animal bones deeply connected to the question of how North America’s megafauna became extinct.

Yet 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, recent years have seen the development of new biomolecular methods of archaeological exploration. Rather than embarking on the excavation of new sites, archaeologists are increasingly turning to the scientific laboratory, using new techniques to probe existing material.

One of these new techniques is called ZooMS, short for Zooarchaeology by Mass Spectrometry. The method relies on the fact that although most of its proteins degrade quickly after an animal dies, some, such as bone collagen, can be preserved for long periods of time. Since collagen proteins often differ in small and subtle ways between different taxonomic groups of animals, and even between individual species, collagen sequences can provide a kind of molecular barcode for identifying fragments of bones that would otherwise be unidentifiable.

Thus, segments of collagen proteins extracted from tiny amounts of bone can be separated and analyzed on a mass spectrometer to perform identification of remaining bones that traditional zooarchaeologists cannot.

Selection of archaeological material to study

The researchers decided to use this method to revisit archived documents from the Smithsonian Museum. Their study was a pilot study that asked the key question: Would the bones stored at the Smithsonian Museum retain enough collagen for us to learn more about the fragmented bones in its stores?

The answer was not obvious, as many excavations had taken place decades ago. Although the materials had been stored for around ten years in a state-of-the-art, climate-controlled facility, the early date of the excavations meant that modern standards were not necessarily applied to their handling, processing and storage on the premises. all the steps.

The team examined bone material from five archaeological sites. The sites were all dated to the Late Pleistocene/Early Holocene (approximately 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 preserve diagnostic characteristics that could allow zooarchaeological identification of a species, genus, or even family. Some bone fragments looked very unpromising: they were bleached and weathered, or their edges were rounded, suggesting that they had been transported by water or sediment before being buried at the site.

Discover excellent biomolecular preservation

What they found surprised them. Despite the age of most of the collections, the unpromising appearance of much of the material, and the ancient origins of the bones themselves, they yielded excellent ZooMS results. In fact, 80% of sampled bones produced sufficient collagen for ZooMS identifications. 73% could be identified at the gender level.

The taxa they identified using ZooMS included Bison, Mammuthus (the genus to which mammoths belong), Camelidae (the camel family), and possibly Mammut (the genus to which mastodons belong). In some cases, they were only able to assign the specimens to 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 essential for identifying the spectra produced by a sample when it is analyzed on a mass spectrometer.

Their findings have major implications for museum collections. The material studied by the researchers is in every way the poor cousin of the glamorous material displayed in natural history museums.

To look at, these very fragmentary, small, and non-diagnostic animal bones are uninteresting and superficially uninformative. But like other biomolecular tools, ZooMS reveals the wealth of information preserved in neglected specimens that have attracted neither the attention of researchers nor visitors for decades.

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

Their research also highlights the importance of preserving archaeological collections. When researchers and institutions are strapped for funding, archaeological objects and bones that are not prestigious or have a clear immediate benefit may be neglected or even discarded. It is essential that museums have adequate funding to maintain and house archaeological remains over the long term.

As their analysis shows, such ancient materials can find new life in unexpected ways – in this case, allowing us to use tiny fragments of bone to help us get one step closer to solving the mystery of disappearance of some of the largest animals ever seen on Earth from the landscapes of ancient North America.