Hippopotamus antiquus

Hippopotamus antiquus is an extinct species of the genus Hippopotamus that ranged across Europe during the Early and Middle Pleistocene. It was considerably larger than the living hippopotamus (Hippopotamus amphibius).

Evolution
H. antiquus is suggested to be closely related to the African species Hippopotamus gorgops, and may be a descendant of that species. The oldest records of H. antiquus date to the Early Pleistocene, around 2.1-2 million years ago, which are found in Italy and Greece. The earliest specimens in the Iberian Peninsula date to around 1.7 million years ago. H. antiquus first became widespread north of the Alps around 1.1 to 1 million years ago, as evidenced from specimens found dating to this time in France, Germany, the Netherlands and southern Britain. The youngest remains of the species are from Condeixa in Portugal, suggested to date to approximately 400,000 years ago, and Malagrotta in central Italy, dating to 450-380,000 years ago. Later records of the genus Hippopotamus in Europe are believed to belong to the modern hippopotamus (Hippopotamus amphibius). The earliest generally accepted record of H. amphibius in Europe is around 500,000 years old, and it is therefore possible that H. antiquus and H. amphibius coexisted in Europe from 500-400,000 years ago, though this is uncertain.

Distribution
H. antiquus ranged across Europe, from the Iberian Peninsula and the Italian Peninsula, to the British Isles to the Rhine River to Greece. The easternmost record of the species is from the Caucasus, at the Akhalkalaki site in Georgia. Remains possibly attributable to the species are also known from the Ubeidiya site in Israel, though other authors assign these remains to the species H. behemoth. Their distribution was strongly controlled by temperature, with the species only extending to the northern parts of Europe during warmer interglacial intervals.

Description
Based on the transverse diameter of its limbs, H. antiquus has been estimated to weigh 3,500–4,200 kg, more than double the weight of the average specimen of H. amphibius. The species exhibited size variability, with individuals from the late Early Pleistocene and Middle Pleistocene being smaller on average than those from earlier in the Early Pleistocene. In comparison to modern Hippopotamus amphibius, the skull is more slender and elongate, but with a shorter neurocranium. Hippopotamus antiquus has been suggested to have been more aquatically adapted than Hippopotamus amphibius, with the skull having more elevated eyesockets and the feet having shorter metapodial bones than H. amphibius. An analysis of nitrogen isotopes suggests that H. antiquus preferred aquatic plants, in contrast to modern H. amphibius, which prefers terrestrial grasses.

The Cretan dwarf hippopotamus (H. creutzburgi) is believed to have evolved from H. antiquus through the process of insular dwarfism on the island of Crete. The extinct Cyprus dwarf hippopotamus (H. minor) may also derive from H. antiquus, but this is uncertain.

Relationship with humans
Remains of the species with cut marks suggestive of butchery by archaic humans have been reported from several sites in Spain, dating to the late Early Pleistocene, including Barranco León (~1.4 Ma), Fuente Nueva 3 (~1.3 Ma), and Vallparadís (~1.0 Ma), At the Marathousa 2 site in Greece, thought to date to the Middle Pleistocene around 500-400,000 years ago, remains of a juvenile Hippopotamus antiquus individual with cut marks were found associated with a lithic artefact. It is unclear whether the remains at these sites were hunted or scavenged. It is unlikely that archaic humans regularly hunted healthy adult hippopotamuses due to their dangerousness.