For the first time, scientists have deciphered the genetic sequence of an extinct species. After painstaking work, scientists at the U.S. Department of Energy (DOE) Joint Genome Institute (JGI) have unveiled the DNA fingerprint of an extinct species of Pleistocene cave bear. The species, Ursus spelaeus, disappeared more than 10,000 years ago. The extinct carnivore is related to both modern-day brown bears (Ursus arctos) and polar bears (Ursus maritimus). The fossil specimens used in the study were recovered from Austria and are estimated to be 40,000 years old.

Piecing together ancient DNA is fraught with challenges. When an animal dies, its DNA begins to degrade immediately. As the carcass decays, microorganisms take over, breaking down the remains and leaving behind their own traces of DNA. When the fossilized remains are finally recovered, anyone who touches them can inadvertently leave behind little touches of their own DNA as well. The result is a mish-mash of genetic material that scientists must sort through in order to extract the DNA of the fossilized beast.

Prior to this study, most genetic research on extinct species focused on mitochondrial DNA. Mitochondrial DNA helps reveal evolutionary relationships among species, but it falls short when trying to describe how an extinct animal differs from related species still alive today.

For this reason, scientists focused not on the bear's mitochondrial DNA but instead on its genomic DNA--DNA that lies at the heart of the fossilized cells: the nucleus. The research team put their lab's computing and DNA extraction skills to work and isolated the bear's DNA. They then compared the bear DNA to dog DNA (dogs share as much as 92 percent of their genetic sequence). This comparison served as a template, a guide for the researchers as they reconstructed bits of bear DNA, placing each fragment in the proper sequence.

But cave bears, though intriguing, are not the ultimate goal of this research. The team has its sights set on another extinct species, one more entwined with our own past: Neandertals. In a press release, Eddy Rubin (DOE JGI director and head of the lab that conducted the sequencing) states:

"We picked cave bear as an initial test case ancient DNA target because the samples we used in the study are roughly the same age as Neandertals. Our real interest is in hominids which include humans and the extinct Neandertal—the only other hominid species that we have to compare with humans. Our nearest living relative is the chimp and that's five million years of divergence. Although we are very similar on a sequence level, there are obvious phenotypic differences. Next, we would like to access and evaluate genomic information about other hominid species, Neandertals in particular, as they represent probably our closest prehistoric relative." ~ Eddy Rubin, DOE JGI director.

Find out more:

• Ancient Bear DNA Mapped (National Geographic)
• DOE JGI Sequences DNA from Extinct Cave Bear (DOE JGI)
• Genomic Sequencing of Pleistocene Cave Bears (Science)