This post is by Erik Ersmark, lead author of the recently published paper “Population Demography and Genetic Diversity in the Pleistocene Cave Lion“. He is a PhD candidate in the Department of Bioinformatics and Genetics at Stockholm University and the Swedish Museum of Natural History, Stockholm, Sweden.
Today’s African savannah boasts an impressive biodiversity of large mammals that is unique in the modern world. However, this kind of ecosystem was not always restricted to the grasslands of Africa. Far back in time a similar steppe stretched across the entire Eurasian continent all the way from Spain to Alaska, a huge northern savannah inhabited by huge mammals. But although similar, it was at the same time quite different: instead of wildebeests, buffalos and elephants, this steppe was home to bison, aurochs and woolly mammoths. Its fauna was well adapted to the prevailing dry and sometimes quite cold conditions, in many cases to such an extent that these animals were only found in this specific environment.
The vast mammoth steppe did not only contain mammoths, horses and other grazers. Preying on the large herbivores were large predators like wolves, sabretooth cats and lions. The lions were of a robust type, slightly larger than their modern counterparts, and although recognized as lions from their remains, no one today knows precisely what they looked like. We know that humans did encounter them far back in time, since they in some cases depicted the lions and thereby provided us with some hints of their appearance. Lions are in fact frequently occurring in Palaeolithic art, perhaps most prolifically and famously so in the cave paintings from the Chauvet cave in France, dating back some 30 thousand years. Cave sites like this have sometimes also contained the actual remains of lions, which has led to the somewhat misleading name given to them – cave lions.
Along with so many other large bodied “cave animals”, the cave lion did not survive into historical times. They went extinct at the end of the Pleistocene era around 14,000 years ago, and around this time the entire mammoth steppe was also fading and it was eventually transformed into woodland and barren tundra.
In order to better understand the population dynamics of the cave lion, we analysed remains gathered from across the former mammoth steppe. We specifically focused on north eastern Siberia, which in the Late Pleistocene was part of Beringia – a vast northern landmass bridging Eurasia and North America. Since the ground is permanently frozen throughout most of this region, the remains found there are usually very well preserved, enough so that it is even possible to extract DNA from them. Together with radiocarbon dating, this DNA provided us with data on how the genetic diversity had changed over time. After all analyses had been performed, the results could give us a glimpse of what had happened to the cave lions of Beringia.
What the results showed was something already suggested in a previous study by Barnett et al. (2009); that the Beringian cave lions had suffered a decline, long before they eventually went extinct. The genetic diversity clearly showed a pattern of a bottleneck having taken place far back in time. By running powerful simulations on our data together with those from the previous study, an estimate was obtained of a decline in population size starting almost 50,000 years ago. This decline seemed to have been both severe and long lasting, because it was not until a few thousand years before its final extinction that the cave lions started to recover.
The question we were left with was why this bottleneck had taken place. What was the underlying cause or causes? What was more, many other large mammals also seem to have suffered declines in Beringia over this time period. This period did coincide with the expansion of a new kind of predator across Eurasia – modern humans. However, there are so far no reliable human traces of that antiquity (the start of the bottleneck) from inside Beringia, which makes us less likely as suspects. Our results open up for many interpretations, but also for many further studies of the lost and diverse fauna of the mammoth steppe.
You can read the full article, completely free, in our latest issue of Open Quaternary.
- Barnett, B. Shapiro, I. Barnes, S.Y.W. Ho, J. Burger, N. Yamaguchi, T.F.G. Higham, T. Wheeler, W. Rosendahl, A.V. Sher, M. Sotnikova, T. Kuznetsova, G.F. Baryshnikov, L.D. Martin, R. Harington, J.A. Burns, A. Cooper, Phylogeography of lions (Panthera leo ssp.) reveals three distinct taxa and a late Pleistocene reduction in genetic diversity, Molecular Ecology, 18 (2009), pp. 1668–1677