Giant German hippopotamuses wallowing on the banks of the Elbe are not a
common sight. Yet 1.8 million years ago hippos were a prominent part of
European wildlife, when mega-fauna such as woolly mammoths and giant
cave bears bestrode the continent. Now palaeontologists writing in Boreas,
believe that the changing climate during the Pleistocene Era may have
forced Europe’s hippos to shrink to pygmy sizes before driving them to
warmer climes.
“Species of hippo ranged across pre-historic Europe, including the giant Hippopotamus
antiquus a huge animal which often weighed up to a tonne more than
today’s African hippos,” said lead author Dr Paul Mazza from the
University of Florence. “While these giants ranged across Spain, Italy
and Germany, ancestors of the modern Hippo, Hippopotamus amphibius,
reached as far north as the British Isles.”
Hippos were a constant feature of European wildlife for 1.4 million
years, during the climatically turbulent time of the Pleistocene era,
which witnessed 17 glacial events. The experience of such environmental
changes would not have been without cost, and Dr Mazza and co-author Dr
Adele Bertini, also from Florence, investigated the impact this changing
climate may have incurred.
The research focused on fossils from across Europe, ranging from the
German town of Untermaßfeld in Thuringia, to Castel di Guido, North of
Rome, and Collecurti and Colle Lepre in Italy’s Central Eastern Marche
province. The fossils were compared to a database of measurements taken
from modern African and fossil European hippos.
“The German fossil from Untermaßfeld is the largest hippo ever found in
Europe, estimated to weigh up to 3.5 tonnes,” said Mazza. “The
Collecurti specimen was also large, but interestingly even though it was
close in both time and distance to the Colle Lepre specimen the latter
specimen was 25% smaller. A final specimen, an old female from Ortona in
central Italy, was smaller again. It was 17% smaller than the Collecurti
fossil and approximately 50% lighter.”
The team found that a clear size threshold separated hippo specimens
which heralded from different parts of the Pleistocene age. The hippos
from the early Pleistocene were the largest ever known while smaller
specimens emerged during the middle Pleistocene. Larger specimens
briefly reappeared during the late Pleistocene.
“We believe the size difference was connected to the changing
environmental conditions throughout the Pleistocene,” said Mazza. “The
Ortona hippo, the smallest of the specimens, lived in a climate where
glacial cycles turned colder, while cold steppes replaced warm ones
across the Mediterranean.”
The drop in temperature and rainfall during the Pleistocene caused
significant changes to plant life across Europe resulting in an
expansion of grassy steppes. Being grazers hippos may have been expected
to thrive in this new environment. Unexpectedly they appeared to shrink,
only re-attaining their past size during the warm periods of the late
Pleistocene, when forests and woodland re-colonised the steppes.
During their time in Europe hippos were forced to live in habitats
influenced by a general environmental trend towards cooler and drier
conditions. In response hippos achieved giant sizes during warmer and
relatively more humid stages, but became smaller, and even very small,
under non-ideal environmental conditions.
“While hippos are normally considered indicators of warm, temperate
habitats this research shows that temperature was not only the
controlling factor for their ancient ancestors,” concluded Mazza. “Our
research suggests other factors, such as food availability, were equally
important. Appreciating the importance of factors beyond temperature is
of great significance as we consider how species may adapt to future
ecological and environmental changes.”
