The image we have of glacial Europe readily evokes a white desert, populated by mammoths and reindeer, swept by cold winds from the north. However, beneath this apparent uniformity, certain valleys sheltered unsuspected ecosystems, capable of supporting unexpected fauna. It is in one of these enclaves, nestled along the Upper Rhine, that researchers have uncovered revealing clues to the past presence of hippos, thereby improving our understanding of the last ice age.
Until now, paleontologists believed that these mammals, today confined to sub-Saharan Africa, had disappeared from Europe around 115,000 years ago, at the end of the last interglacial period. However, carbon-14 dating, combined with the study of ancient DNA, revealed a very different scenario. According to results published in the journal Current Biology, hippos survived several tens of thousands of years after this date, occupying a region that offered much milder conditions than imagined.
The fossils studied mainly come from the area around Mannheim and Bobenheim-Roxheim in southwestern Germany. Despite the passage of time, their state of conservation has proven to be exceptional. The researchers were able to extract intact collagen, essential for radiocarbon analyses, and DNA fragments preserved in the bones. As SciTechDaily reports, these data show a striking genetic proximity between European hippos and those currently living in Africa, confirming that they indeed belonged to the same species.
When hippos defied the glacial cold
The presence of a tropical animal in a frigid Europe is surprising. However, the climate archives explain this paradox. During the so-called Middle Weichselian period, the Rhine valley benefited from phases of regularly milder temperatures, called interstadials. These episodes, long enough to avoid the total freezing of rivers and maintain aquatic vegetation, offered an improbable refuge to these water-dependent animals.
Analyzes of pollen and fossilized wood carried out in the same area confirm this relative softness. Tree species such as oak and pine bear witness to an alternation between temperate forests and more open landscapes, where mammoths, woolly rhinoceroses and hippos coexisted. These results revise the traditional chronology of large Pleistocene mammals. They show that the boundaries between “warm” and “cold” faunas were much more fluid than what the classic model of strict alternation between glaciations and interglacials suggested.
This specific adaptation undoubtedly reflects the ability of certain groups of hippos to move according to climatic cycles. Their populations were small, isolated and genetically not very diverse, as shown by the analysis of the ancient genome carried out by the Potsdam team. This weak mixing suggests the existence of small surviving nuclei, confined in pockets of temperate environments which then punctuated the continent.
Rewriting the history of European wildlife
This discovery calls into question the simplified vision of an icy Europe uniformly hostile to life. The Upper Rhine now appears to be a real refuge for species usually associated with tropical climates. By demonstrating that hippos survived beyond the last interglacial period, the researchers invite a reconsideration of the true age of other European fossils traditionally attributed to this warmer era.
For paleontologist Wilfried Rosendahl, director of the Reiss-Engelhorn-Museen in Mannheim, these results prove that the Ice Age was not a homogeneous block of cold, but a mosaic of microclimates with complex local dynamics. These variations shaped the distribution of species, creating refuges where certain tropical faunas were able to persist briefly before disappearing again when conditions worsened.
This rereading of the past also allows us to better understand the link between climate and biodiversity. Indeed, rapid variations in climate can modify the distribution of species in a short time. Europe during the last glaciation was therefore not just an icy desert populated by mammoths. In certain sheltered places, hippos still lived, reminding us that life always adapts, even in the face of difficult conditions.
