Were Pleistocene hippopotamuses exposed to climate-driven body size changes?

The study proposes a working hypothesis that Mediterranean hippopotamuses, and perhaps European ones as well, reduced their size, sometimes even drastically, from the “Mid-Pleistocene revolution” (MPR, ~1.2÷0.5 Ma) to the Late Pleistocene. This was a turning point for glacial/interglacial cycling: glacial phases lasted longer (up to 85 ka) and alternated with shorter interglacial phases (up to 15 ka). In the course of the Middle-Late Pleistocene relatively larger hippopotamuses have been found at warmer and somewhat more humid intervals. Data seems indicating that they might not have grown such as large under less favourable conditions, i.e., at colder and comparatively drier times. Food availability and not necessarily ambient temperature and precipitation alone can be a possible explanation of the phenomenon, but we cannot exclude possible side effects of Pleistocene habitat fragmentation. In fact, the environmental breakup during the advanced part of the Quaternary led to the isolation of megafauna populations which might have underwent some sort of insular kind of modification. Although the amount of remains available is still limited, it is nonetheless a fact that hippopotamuses changed their body size through time, normally turning comparatively smaller. If the conclusions drawn here will be confirmed, as data continue to accumulate, hippopotamuses might cast doubts on the generality of Bergmann’s rule.