Body mass estimate and in-vivo reconstruction of Hippopotamus antiquus from Figline, Upper Valdarno (Tuscany)

Hippopotamus antiquus was an extinct semiaquatic megaherbivore foraging mainly on aquatic vegetation, with a biochronological range in the Italian peninsula spanning from around 2.2 to 0.4 Ma. Considering its large body size, and its lifestyle considered to be more aquatic than the current form H. amphibius, a correct estimate of the body mass is interesting to correctly interpret various biological aspects of this extinct megaherbivore. In this contribution, we propose an estimate of the body mass of H. antiquus by comparing the results obtained with classical regression formulae with the values obtained through a new 3D volumetric approach. For both approaches, we used the mounted specimen on display at the Museum of Geology and Palaeontology of the University of Florence. As already found in recent contributions, the estimates obtained with the regression methods provide very high ranges compared to the volumetric approach, with minimum estimates of 200 kg and maximum estimates of over 6 tons, completely incompatible with a tetrapod of this size. The new volumetric estimate provides an average value for the BM in H. antiquus of approximately 3170 tons, thus confirming a body weight approximately double compared to the average values in the extant species H. amphibius.