Blog

50,000 years ago, North America was ruled by megafauna. Clumsy mammoths roamed the tundra, while the forests were home to towering mastodons, ferocious saber-toothed tigers and huge wolves. Bison and unusually tall camels moved in herds across the continent, while giant beavers roamed the lakes and ponds. Huge ground sloths weighing over 1,000 kg are found in 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 that the arrival of humans was key. Perhaps animals were hunted and eaten, or perhaps humans simply changed their habitats or competed for vital food sources.

But other researchers say climate change is to blame as the Earth thaws after several thousand years of glacial temperatures, changing the environment faster than the megafauna can adapt. The differences between these two schools are fierce and the debates are contentious.

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

While some sites preserve the remains of the megafauna really well, the conditions in others are hard on the animal bones, breaking them down into smaller fragments that are too altered to be identified. These decay processes include exposure, abrasion, breakage, and biomolecular degradation.

Such problems leave us without critical information about where certain species of megafauna were distributed, exactly when they became extinct, and how they responded to the arrival of humans or environmental climatic changes in the late Pleistocene.

Applying modern technology to old bones

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

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

Fortunately, recent years have seen the development of new biomolecular methods for archaeological investigation. Rather than setting out to excavate 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 an animal dies, some, such as bone collagen, can be preserved for long periods of time. Because collagen proteins often 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 otherwise unidentifiable bone fragments.

Thus, collagen protein segments extracted from small amounts of bone can be separated and analyzed on a mass spectrometer to perform identifications of residual bones that traditional zooarchaeologists cannot.

Selection of archaeological material for research

The researchers decided to use this method to review the archive material of the Smithsonian Museum. Their study was a pilot that asked the key question: Will the bones stored 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 were carried out decades ago. Although the material has been stored for the past decade or more in a state-of-the-art, climate-controlled facility, the early date of the excavation means that modern standards were not necessarily applied to its handling, processing and storage at all stages.

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

Although some of the material from the sites could be identified, much of it was highly fragmented and did not preserve diagnostic features that could allow zooarchaeological identification to species, genus, or even family. Some of the bone fragments looked extremely unpromising – they were bleached and weathered, or had rounded edges, suggesting they had been transported by water or sediment prior to burial at the site.

Discovery of excellent biomolecular storage

What they found surprised them. Despite the age of many of the collections, the unpromising appearance of much of the material, and the ancient origin of the bones themselves, they yielded excellent ZooMS results. In fact, a remarkable 80% of the bone samples taken yielded enough collagen for ZooMS identifications. 73% could be identified to genus 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 can only assign specimens to broad taxonomic groups because many North American animals do not yet have ZooMS reference libraries. These databases, which are relatively well developed for Eurasia but not for other regions, are essential for identifying the spectra that a sample produces when it is run through a mass spectrometer.

Their discoveries are of great importance to museum collections. The material the researchers are looking at is, in every way, the poor cousin of the glittery stuff on display in natural history museums.

To look at them, these highly fragmented, small and non-diagnostic animal bones are uninspiring and superficially uninformative. But like other biomolecular tools, ZooMS is revealing the wealth of information preserved in neglected specimens that have not attracted the attention of either researchers or visitors for decades.

The results also highlight the potential of such collections to address ongoing debates about 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 address long-standing questions about megafauna extinction. ZooMS offers a relatively easy, fast and inexpensive way to extract new information from long-excavated objects.

Their research also highlights the importance of preserving archaeological collections. When researchers and institutions are constrained by funding, archaeological artifacts and bones that are not glamorous or of obvious immediate utility may be overlooked or even discarded. It is extremely important that museums are provided with adequate funding to care for and preserve archaeological remains 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 get a little closer to solving the mystery of why some of Earth’s largest animals are disappeared from the landscapes of ancient North America.