Climate change spelled doom for Woolly Rhinos 14,000 years ago, study says

Woolly rhinos went extinct at the end of the last ice age in Siberia about 14,000 years ago, and now ancient DNA is helping to shed light on what really happened to them and other large mammals. Previously, it was believed that humans hunted these giant animals as they spread across the globe. But new research has suggested that climate change is the culprit, according to a new study based on sequencing ancient DNA from the well-preserved remains of 14 woolly rhinos.

It is really amazing that the researchers can read the DNA sequences, even the entire genomes, from these long-extinct animals. It is a bit like having a time machine where they can travel back through time and study evolutionary change as it is happening in real-time. Given the climate where these animals lived and died, the cold conditions helped preserve their DNA.

While obtaining high quality DNA is difficult, the researchers are lucky to work on specimens that have been preserved in the permafrost for thousands of years. In a way, it is like opening a freezer that was closed during the last Ice Age. The study published Thursday in the journal Current Biology. Rather than disappearing due to overhunting by early humans, woolly rhino populations actually seemed to thrive and remain incredibly diverse before they went extinct.

Recent research has also shifted back the timeline for humans living in Siberia.

Originally, it was believed humans arrived between 14,000 and 15,000 years ago. New evidence has pushed human occupation back to sites that are at least 30,000 years old, so the arrival of humans no longer coincides with the demise of woolly rhinos. Instead, the DNA the researchers studied revealed more of a population boom for woolly rhinos during that time.

The DNA was retrieved from tissue, bone, and hair samples from 14 woolly rhino specimens that lived across Siberia. The scientists were able to determine information about the population sizes and genetic diversity of these woolly rhinos stretching back for tens of thousands of years before they went extinct. The researchers were surprised to discover that woolly rhinos had a much higher genetic diversity than any living rhino, woolly mammoths, or even modern humans.

The woolly rhinos also appeared to go extinct suddenly, rather than gradually, and did not experience much inbreeding. Inbreeding tends to increase as populations decline, and it occurred in the last woolly mammoths before they went extinct. The researchers also found genetic mutations in the woolly rhino DNA that helped them adapt to life in the bitterly cold weather of the last ice age, including a receptor in the skin that could sense temperature variations.

Woolly mammoths also had this adaptation.

About 29,000 years ago, the woolly rhino population swelled as the ice age intensified and remained stable with little inbreeding. The data provided by the DNA followed the woolly rhino population until about 18,500 years ago, which was about 4,500 years before they went extinct. This tells the researchers that the cause for their extinction occurred during that 4,500-year gap.

A sudden but brief period of warming temperatures occurred toward the end of the last ice age. This event, called the Bølling-Allerød interstadial, happened between 12,890 and 14,690 years ago. The temperature change was fast. Some records from ice cores taken on Greenland suggest an increase in temperature by 18 degrees Fahrenheit, possibly within as little as a few decades.

The large grasslands where the woolly rhinos roamed, called a steppe environment, would have been replaced by trees and shrubs in response to the warming as well. Like woolly mammoths, woolly rhinos were covered in thick fur and perfectly suited to their cold environment, grazing across the Siberian tundra. Both had adaptations that helped them thrive during the last ice age. But mammoths were about three times bigger, had a more flexible diet, and lived in matriarchal herds.

The woolly rhinos were likely more solitary.

And the woolly mammoths did not experience an increase in population size as the woolly rhinos did 29,000 years ago. Now the researchers want to study DNA from woolly rhinos that lived during those last 4,500 years before they went extinct. The scientists also want to investigate other large animals that had adapted to such cold conditions to see how they were affected by a warmer and less stable climate.

This includes cave lions, wolves, mammoths, horses, and steppe bison. The researchers are coming away from the idea of humans taking over everything as soon as they come into an environment. Although they can not rule out human involvement, the researchers suggest that the woolly rhinoceros’ extinction was more likely related to climate change.

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