eFfing Fossil Friday: Frozen Femur

A 45,000 year old human femur from Siberia provides new information about genetic mutation rates and modern human origins. As Quiaomei Fu and colleagues report in this week’s issue of Nature, this seemingly simple leg bone carries so much information, not because of its gross anatomy, but because of the ancient DNA it preserves.

The femur wasn’t discovered by paleontologists, but by an artist/historian looking for fossils around the Irtysh River. The bone came from from a site called Ust’-Ishim, only some 650 km north of the snowy capital where I work in Kazakhstan:

Ust'-Ishim

The site in question, Ust’-Ishim is marked by the yellow star. The red and blue sites to the southeast are other Upper Paleolithic sites. Okladnikov (3) and Denisova (4) have also yielded fossils preserving ancient DNA. Modified from Fu et al. figure 1.

The bone was directly radiocarbon dated to around 45,000 years ago. With a fairly precise age of the bone, Fu et al. could estimate the rate at which genetic mutations arise, by counting the number of new mutations in recent humans that aren’t shared by the Ust’-Ishim femur. This led to an estimate of around 0.43×10−9  new mutations per site per year. This is a relatively low rate compared to estimates based on geologically older fossils, but consistent with more recent estimates that directly compare parents and offspring.

The Ust’-Ishim individual had levels of Neandertal ancestry comparable to living Eurasians (~2.3% of the genome), but there is no evidence of any Denisovan ancestry. Because this individual lived closer to the date of modern-Neandertal admixture, the Neandertal segments of its genome are longer than in modern people (recombination over generations breaks these regions apart into shorter segments). Knowing about recombination rates, Fu et al. could infer that admixture between Neandertal and modern human populations occurred between 50-60,000 years ago.

This eFfing Friday fossil provides more tantalizing evidence for DNA-bearing human fossils just across the Kazakhstan border. With Ust’-Ishim to the north, Denisova and Okladnikov caves to the east, and Teshik Tash to the south, my colleagues and I are very keen to find similar sites here on the KZ side.

Reference: Fu et al. 2014. Genome sequence of a 45,000-year-old modern human from Siberia. Nature 514: 445–449. doi:10.1038/nature13810.

Advertisements

Kazakhstan Paleolithic fieldwork: Valikhanova

Last week, I left my home in Astana for southern Kazakhstan, to rendezvous with researchers based in Kazakhstan, the United States and Germany. This is the beginning of a collaborative effort to understand the underappreciated importance of Kazakhstan in hominin evolution.

Post-fieldwork meal. From foreground clockwise: Zhaken Taimagambetov (1), Tyler (2), Saya (1), Jason (2), Adam (3), Radu (4), Mica (2), Kat (5), Katie (2), and Rinato (1). Not pictured: Me (6) and Jean-Marc (1). Numbers indicate school affiliations, at the end of the post.

We just returned from a brief stint of soil sampling at, and site surveying around, the Paleolithic site of Valikhanova, near the town of Zhanatas. This site was excavated decades ago, and has yielded a number of stone tools interpreted as transitional between Middle and Upper Paleolithic industries. This is a fascinating period for ‘modern’ human origins, but unfortunately the site has not yielded any human fossils to the best of my knowledge.

Valikhanova. The excavation site is the layered earth exposure on the right, our camp site on the left.

But there are other important questions that can be asked about the nature of the site and its inhabitants. First, the geological layers (“strata”) of the site have not been reliably dated, so soil samples were collected to be analyzed by a dating technique called optically stimulated luminescence (this is the work of Dr. Kat Fitzsimmons). Second, aspects of climate and ecology can be inferred from soil chemistry, which is the focus of team members from Colorado State University. Combining this information, we can begin to understand when and why humans (Neandertal and/or more ‘modern’ looking) inhabited the area – e.g., was it only between major glacial periods, how much time does the site span, etc?

And it’s a pretty amazing area. The site is nestled in a depression, creating an ecosystem somewhat protected from harsh winds and temperatures blowing around surrounding the mountains. That said, the night we arrived we were welcomed by extremely high-speed winds and heavy rains. My tent was the only casualty of the storm, forcing me to flee to the comforting confines of our sturdy truck and cups of vodka. The storm was short lived, and soon the sky opened up to a panoramic harlequin sunset.

Palette after the storm. Left to right covers from West to East. The excavation and North are at the center.

Also there was a rainbow.

My main activity here was survey, the search for other places that could potentially yield fossil and additional cultural materials. Survey basically involves a fairly targeted scouring of a landscape, searching for specific features. Our survey took us over and across gorgeous landscapes. We found a number of possible fossil/artifact accumulations and possible caves/rock shelters for future investigation, but no human fossils turned up (this was not terribly surprising, as human fossils are quite rare).

Atop one big hill, Drs. Jason LaBelle and Adam Van Arsdale discuss one of many stone tools we found littering the area around Valikhanova.

One neat surprise did come when scanning the ground above a rocky outcrop over a filled-in cave. At first glance, I seem to be holding some kind of a jaw bone fragmentwith two teeth. Close inspection shows this just to be a rock with a coincidentally-molar-like calcification. Bummer. However, we were able to trick one expert into thinking for a minute that we found some kind of pig or other mammal fossil.

Fossil bovid, equid or suid? Meganthropus?! Just a rock? Osteology students & paleontologists, beware faux-ssils…

We’re briefly back in Almaty to recharge, and on Tuesday we’ll head out to explore Charyn Canyon for a few days. Stay tuned for more about our adventures!

*Affiliations from Fig. 1 above:
1. Kazakh National University, 2. Colorado State University, 3. Wellesley College, 4. Römisch-Germanisches Zentralmuseum, 5. Max Planck Institute. 6. Nazarbayev University.