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Hippos from Central Europe were assumed to have gone extinct around 115,000 years ago when the temperate conditions of the region transitioned into an icy one with the end of the last interglacial period and the beginning of the last Ice Age.

A published in Current Biology has rewritten the timeline of hippo history in central Europe, using radiocarbon dating on fossil remains from the Upper Rhine Graben, Germany鈥攁 fossil-rich site that serves as a natural archive of the continent's climate past.

The researchers discovered that these massive mammals didn't vanish when the climate cooled 115,000 years ago. The fossils were approximately 47,000 to 31,000 years old, suggesting that the mighty creatures held on far longer than expected, surviving deep into the last Ice Age.

The warm summers of Central Europe were soon replaced by icy days and nights during the last glacial period, known as the Weichselian glaciation, which began approximately 115,000 years ago and lasted until around 11,700 years ago.

Hippos need mild climates with plenty of vegetation and unfrozen water to survive, which is why they are often seen as a clear indicator of warm interglacial periods. Based on this, scientists long believed that hippos vanished from central Europe at the very onset of the Ice Age, when colder conditions and scarce vegetation made the region unsuitable for them.

This assumption was further strengthened by how fossil evidence was interpreted. Sites such as those in the Upper Rhine Graben were traditionally thought to capture the shift from the warm Eemian, the last interglacial period, to the cold early Weichselian. As a result, any hippo fossil discovered within these layers was automatically assigned to the Eemian period.

However, the exact timing of hippo extinction in Europe remained uncertain, largely because scientists lacked ancient DNA from these Ice Age giants. Without molecular evidence, they couldn't even determine if the extinct European populations were genetically related to their modern-day African hippos, leaving key evolutionary questions unresolved.

To solve this mystery, the researchers analyzed 19 hippo fossils found in the Upper Rhine Graben and extracted a partial paleogenome from one of the samples. They then compared the ancient genetic data against modern hippo genomes to trace the evolutionary relationships between the extinct European population and today's African hippos.

The results indicated that the Ice Age hippos were closely related to today's African common hippos.

To determine the exact time these animals lived, the team employed radiocarbon dating and amino acid geochronology. The calculations showed that instead of disappearing over 115,000 years ago, as scientists once believed, these hippos were still around as recently as 31,000 years ago, which was deep into the Ice Age. The dating of other Ice Age animals from the same site, like woolly mammoths and woolly rhinos, confirmed these results.

The hippos likely survived because the glacial period was not consistently harsh. Instead, there were periodic warm phases known as interstadials that created localized refuges in the Upper Rhine Graben, with enough unfrozen water and vegetation to support them. However, the genome revealed low diversity, indicating these hippos belonged to a small, isolated population rather than a large, interconnected one.

The researchers suggest that the survival of the hippos may not represent one population stubbornly persisting throughout the Ice Age, but rather a series of short-term recolonization events in which the creatures moved in during warmer phases and left when the conditions became inhospitable.

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