A group of mammals went extinct thousands of years ago. Ancient bone collagen might be the key to unlocking this mystery.
Ice Age Mystery
Fifty thousand years ago, North America was once dominated by megafauna, such as mammoths, saber-toothed tigers, bison, tall camels, and giant beavers. However, sometime at the end of the Last Glacial Period, most of these giants disappeared.
What happened to these large animals remains a subject of debate. Some scientists believe the megafauna were wiped out by the arrival of humans, as they were hunted and eaten or their habitats were altered.
But other experts argue that climate change was to blame. As our planet thawed after thousands of years of glacial temperatures, the environments changed faster than megafauna could adapt.
The Ice Age mystery remains unanswered despite decades of research. Scientists do not have enough evidence to rule out one theory or the other. One reason is that most of the bones of megafauna are fragmented and are difficult to identify.
Some sites are good in preserving megafaunal remains, but the conditions at others have been harsh on the animal bones. As a result, the bones are worn down into smaller fragments which are too altered to be studied.
These problems leave experts lacking vital information about where megafaunal species were distributed when they disappeared, how they adapted to the environmental changes in the Late Pleistocene, and how they responded to the arrival of humans.
Analyzing Bone Collagen With ZooMS
In a recent study, a team of researchers set out to address this information deficit by turning their attention to the collections of the Smithsonian National Museum of Natural History in Washington, DC. The museum is a reservoir of animal bones that are deeply relevant to the mystery of megafaunal extinction.
Most of the remains in the museum are heavily fragmented and unidentifiable, so their ability to provide the long-sought answer has been limited. Fortunately, new biomolecular techniques of archeological exploration enabled the scientists to probe existing materials in the laboratory instead of heading out to excavate new sites.
One of these new techniques is called Zooarchaeology by Mass Spectrometry (ZooMS). This approach relies on the fact that while most proteins quickly degrade after the animal dies, some can preserve over long time periods, like bone collagen.
Collagen proteins differ in small ways between various taxonomic groups of animals. They can also provide a type of molecular barcode to help identify bone fragments that are otherwise unidentifiable. This means that collagen proteins extracted from small quantities of bones can be analyzed on a mass spectrometer to identify bone remnants, which traditional zooarchaeologists cannot.
In this study, the research team examined bone materials from five archaeological sites in the western US which all dated to the Late Pleistocene or earlier. The latest that had been excavated in 1981, while the earliest was in 1934.
Some of the material from the sites were identifiable, but most of it did not retain diagnostic features that can enable zooarchaeological identification. The researchers also found bone fragments which were bleached, weathered, or edge-rounded, an indication that they had been transported by water or sediment before settling at the burial site.
The team has only conducted pilot ZooMS screening on the bone fragments. Still, the experts are able to retrieve taxonomic information from 80% of the analyzed samples.
The results of the analysis emphasize the potential of bone collections in addressing the debates about when, where, and how large mammals went extinct in North America. It also shows the potential of ZooMS in providing an easy and cheap way to extract new information from ancient excavation sites.
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