The Megafauna Mystery: Scientists Uncover New Clues to What Happened to North America’s Largest Animals

New research explores the unsolved mystery of the extinction of North America’s ancient megafauna, highlighting new research using ZooMS to analyze fragmented bones from the Smithsonian’s collections. It highlights the importance of preserving archaeological collections for uncovering details of past lives and extinctions.

Dr. Mariya Antonosyan, a molecular archaeologist at the Max Planck Institute of Geoanthropology, Dr. Torben Rick, curator at the Smithsonian National Museum of Natural History, and Prof. Nicole Boivin, also of the Max Planck Institute, collaborated on a recent article published in Frontiers in mammal science. Using innovative methods, they analyzed fossil bone fragments at the Smithsonian’s National Museum of Natural History. Their research provides new insights that could advance our understanding of the factors and consequences associated with large mammal extinctions.

50,000 years ago, North America was ruled by megafauna. Lumbering mammoths roamed the tundra, while the forests were home to towering mastodons, ferocious sabre-tooth tigers and enormous wolves. Bison and extremely large camels roamed the continent in herds, while giant beavers roamed the lakes and ponds. Huge ground sloths weighing more than 2,000 pounds (1,000 kg) were found in many areas east of the Rocky Mountains.

And then, sometime near the end of the last ice age, most of North America’s megafauna disappeared. The how and why remain hotly contested. Some researchers believe that the arrival of humans was crucial. Perhaps the animals were hunted and eaten, or perhaps humans simply changed their habitat or competed for vital food resources. But other researchers argue that climate change was the cause, because the Earth thawed after several thousand years of icy temperatures, changing the environment faster than the megafauna could adapt. The disagreement between these two schools was fierce and the debates were controversial.

Despite decades of research, this ice age mystery remains unsolved. We simply don’t have enough evidence at this point to rule out one scenario or the other – or even other explanations that have been proposed (e.g. disease, a comet impact event, a combination of factors). One reason is that many of the bones we use to map the presence of megafauna are fragmented and difficult to identify. While in some locations the remains of megafauns are very well preserved, in other locations conditions have been harsh on the animals’ bones, causing them to be worn down into smaller fragments that are too altered to identify. These decay processes include exposure, wear, fracture and biomolecular decay.

Such problems leave us lacking critical information about where certain megafaunals are located kind were distributed, exactly when they disappeared, and how they responded to the arrival of humans or the climate change of Late Pleistocene environments.

Applying modern technology to ancient bones

Our work aims to address this information gap. To do this, we turned our attention to the exceptional collections of the Smithsonian National Museum of Natural History in Washington, DC. The museum houses the findings of numerous archaeological digs conducted over the past hundred years and is an extraordinary reservoir of animal bones of great importance 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, new biomolecular methods for archaeological research have 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 of those new techniques is called ZooMS – an abbreviation of Zooarchaeology by Mass Spectrometry. The method is based on the fact that while most proteins are broken down quickly after an animal dies, some, such as bone collagen, can be stored for long periods. Because collagen proteins often differ in small, subtle ways among 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. Collagen protein segments extracted from minute amounts of bone can thus be separated and analyzed on a mass spectrometer to make the identifications of surviving bones that traditional zooarchaeologists cannot.

Selecting archaeological material for study

We decided to use this method to revisit the Smithsonian Museum’s archived materials. Our study was a pilot study that asked the most important question: Would the bones at the Smithsonian Museum retain enough collagen so that we can learn more about the fragmented bone material in the storage areas? The answer was not obvious, because many of the excavations had taken place decades ago. Although the material had been stored in a state-of-the-art, climate-controlled facility for the past decade, the early date of the excavations meant that modern standards were not necessarily applied to its handling, processing and storage. all phases.

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

Although some of the material from the sites was identifiable, much of it was highly fragmented and did not retain diagnostic features that would allow zooarchaeological identification of species, genera, or even families. Some bone fragments looked unpromising: they were bleached and weathered, or had a rounded edge, indicating that they had been transported by water or sediment to the site before burial.

Discovering excellent biomolecular preservation

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

The taxa we identified using ZooMS are 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, we were only able to assign the specimens to broad taxonomic groups, as many North American animals still do not 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 we run it on a mass spectrometer.

Our findings have major implications for museum collections. The material we have been looking at is, for all intents and purposes, the poor cousin of the glamorous material on display in natural history museums. At first glance, these very fragmentary, small and non-diagnostic animal bones are uninspiring and superficially uninformative. But like other biomolecular tools, ZooMS reveals the rich information held in neglected specimens that have not attracted the attention of researchers or visitors for decades.

Our results also highlight the potential of such collections to inform ongoing debates about when, where, and how exactly megafauna became extinct. By opening itself up to analysis of the fragmented bone material that makes up much of the megafaunal record, ZooMS has the potential to help provide much new research data to answer long-standing questions about megafaunal extinction. ZooMS provides a relatively easy, fast and inexpensive way to extract new information from long-excavated sites.

Our research also underlines the importance of preserving archaeological collections. When researchers and institutions are strapped for cash, archaeological artifacts and bones that are not glamorous or do not provide a clear immediate benefit may be neglected or even thrown away. It is crucial that museums receive sufficient funding to care for and house archaeological remains in the long term. As our analysis shows, such ancient material can find new life in unexpected ways – in this case, we can use tiny bone fragments to get a little closer to solving the mystery of why some of the largest animals ever to walk the planet have disappeared from the landscape of ancient North America.

Reference: “A new legacy: potential of zooarchaeology through mass spectrometry in the analysis of North American megafaunal remains” by Mariya Antonosyan, Eden Hill, Margaret Jodry, Noel Amano, Samantha Brown, Torben Rick and Nicole Boivin, April 24, 2024, Frontiers in mammal science.
DOI: 10.3389/fmamm.2024.1399358

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