Hippopotamus gorgops

Hippopotamus gorgops is an extinct species of Hippopotamus known from remains found in Northern and Eastern Africa as well as the Levant. One of the largest hippopotamus species, it first appeared during the late Pliocene-Early Pleistocene, and became extinct during the early Middle Pleistocene.

Taxonomy
The species was described by German scientist Wilhelm Otto Dietrich in 1928. It is closely related and possibly ancestral to the large European species Hippopotamus antiquus.

Distribution
Hippopotamus gorgops is known from remains found across Northern and Eastern Africa, spanning from the Late Pliocene-Early Pleistocene boundary to the early Middle Pleistocene. The species, along with other hippopotamids, was abundant at Buia in present-day Eritrea. Remains assigned to H. gorgops alongside the species H. behemoth are known from the Ubeidiya locality in Israel, dating to approximately 1.6 million years ago, with some authors suggesting that H. behemoth is actually a synonym of H. gorgops, given their similar morphology.

Description
H. gorgops grew substantially larger than the living hippopotamus (H. amphibius), with an estimated body mass of over 4000 kg. In comparison to H. amphibius, the orbits and nasal openings are elevated higher above the rest of the skull, with the temporal fossa being shorter, resulting in the distance between the orbits and occiput being shorter. This likely meant a more forward attachment of the temporal muscles. The nuchal and sagittal crests were also proportionally taller, and the palate was elongate. In life H. gorgops would have likely greatly resembled H. amphibius.

Ecology
Isotopic analysis of specimens from the Lake Turkana Basin suggests a high consumption of C4 plants. For specimens from Olduvai Gorge in Tanzania, dental microwear suggests a mixed feeding diet (including both browse and grass), while mesowear suggests a largely grazing diet. The elevated orbits have led to suggestions of a more aquatic lifestyle than H. amphibius, though its robust limbs indicate that it was probably capable of moving efficiently on land, like H. amphibius.

Relationship with humans
Remains with cut or fracture marks from sites across Africa from the Early Pleistocene indicate that H. gorgops was butchered by archaic humans. These include El-Kherba in Algeria, dating to around 1.8 million years ago (mya), Kilombe caldera in Kenya, dating to around 1.76 mya, and the Buia site in Eritrea dating to the late Early Pleistocene, around 1 mya. Often at these sites tools from the Oldowan industry are present. At Kilombe and Buia, it is unclear whether the hippos were hunted or scavenged. It is unlikely that healthy adult individuals were hunted, as with living hippopotamuses, they were likely dangerous.