With its thick fleece to ward off the cold, the woolly rhinoceros is, like the woolly mammoth, an emblematic species of the Ice Age. Extinct about 10,000 years ago, for reasons that remain unclear, it was once legion: remains of this mammal have been unearthed in Europe as well as in northeastern Siberia.
What was his background? When did it occupy each of the two regions at the extremities of Eurasia? These are riddles that DNA analysis is now beginning to solve.
Not without difficulty, for geneticists. While the ancient DNA that lies dormant in the icy soil of northern Asia is relatively well preserved, it does not tolerate our temperate climates very well. For this reason, the DNA of European woolly rhinos has never been exploited until now. Until use... fossilized hyena droppings.
In a study published Wednesday in the journal Biology Letters, Peter Seeber's team from the University of Konstanz in Germany says they have analysed coprolites (the name given to these droppings that have survived through the ages) discovered in two caves in the ultra-Rhine region.
A 'technical feat'
Apart from the DNA of the cave hyena, also extinct, they found that of the woolly rhinoceros, a delicacy of choice for this cousin of the felines, which would prove to be a rich source of information. Who says small animals don't eat big ones?
"It's a technical feat to differentiate between the different types of DNA, that of the predator and its prey, because the hyena had consumed several different species, drunk water in which there were organisms, breathed pollen... That was a bunch of genetic information. Succeeding in separating them is a very interesting step forward," says Antigone Uzunidis, a palaeontologist at the University of Aix-Marseille.
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As this specialist points out, the hyena coprolite is not a spur like any other for those who investigate the distant past of animals: "This carnivore eats bones that will be dissolved by the acid in its stomach and will form a gangue that will protect the smallest elements inside." So these droppings, and even the fossilized vomit of hyenas, are ancient DNA's best friends.
Caution on interpretation
One of the samples was particularly instructive. It has made it possible to reconstruct for the first time the so-called "mitochondrial" genome of a European woolly rhinoceros, a DNA sequence that is only transmitted by the mother and makes it possible to trace female lineages back to the origin of species.
Thus, the study suggests that the European woolly rhinoceros and its Siberian counterpart separated very early, about 450,000 years ago. However, the fossils found in Europe seem to tell the same story. "Their model and interpretation match well with palaeontology data," comments Jean-Philip Brugal, research director at the CNRS, who nevertheless points out a number of shortcomings in the study.
"What this may mean is that rhinos have been able to adapt over a long period of time to Europe's changing environmental conditions," says Uzunidis, who also cites preliminary results.
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The authors of the study themselves caution against over-interpreting their analyses, which are certainly promising, but obtained using a single sample. Finding woolly rhinoceros in hyena droppings was not their original goal. As Laura Epp from the University of Konstanz explains, they were primarily looking for DNA data to allow them to carry out "environmental reconstruction", in particular by guessing which plants grew there: "We are completing this work to allow a better understanding of the environment in which the Neanderthals of the region also evolved."