The modern hippopotamus, represented by the massive Common Hippopotamus and the smaller, elusive Pygmy Hippopotamus, stands as a symbol of African river systems. These two species are the only surviving members of a lineage that has been present on Earth for millions of years. The fossil record indicates the Hippopotamidae family has been a distinct part of the global fauna for at least the last seven to eight million years.
The Hippo’s Closest Living Relatives
The hippopotamus was long classified alongside pigs and peccaries due to superficial similarities in body structure and dental patterns. However, advanced molecular and genetic analysis revealed a surprising evolutionary connection. Scientists discovered that the closest living relatives of the hippos are not other large terrestrial mammals, but rather the fully aquatic cetaceans, which include whales, dolphins, and porpoises. This unexpected pairing is recognized scientifically within a group called Whippomorpha. The two lineages are thought to have separated from a common semi-aquatic ancestor approximately 50 to 60 million years ago. This shared ancestry explains physiological traits, such as their smooth, nearly hairless skin and the unique habit of giving birth and suckling their young underwater.
Tracing the Origins of the Hippopotamidae Family
The first recognizable members of the Hippopotamidae family appear in the fossil record of Africa and the Arabian Peninsula during the Late Miocene epoch, dating back approximately 7.4 million years ago. This emergence is linked to an earlier group of extinct semi-aquatic mammals known as anthracotheres, which are considered the direct ancestors of the hippo family.
An early, enigmatic genus named Kenyapotamus is known from fossils in East Africa, existing between 15 and 9 million years ago. A later, better-identified genus called Archaeopotamus lived across Africa and the Middle East approximately 7.5 to 2.58 million years ago.
The diversification of these early hippos coincided with a significant ecological shift on the African continent. This period saw the expansion of C4 grasslands, which provided a new food source and habitat. This allowed hippos to rapidly establish themselves and spread out of Africa into Eurasia by around six million years ago.
Extinct Hippo Diversity and Geographic Range Contraction
The family’s success throughout the Pliocene and Pleistocene epochs led to greater diversity and a broader geographic distribution than seen today. During the Pleistocene, the Common Hippopotamus (Hippopotamus amphibius) dispersed widely, with remains found across Europe, reaching Great Britain during warm interglacial periods. Another extinct species, Hippopotamus antiquus, was the dominant hippo in Europe from the Early Pleistocene, around 2.1 million years ago, until the modern species replaced it.
Several unique dwarf hippo species evolved in isolation on Mediterranean islands. Fossils of the Cyprus dwarf hippopotamus (Hippopotamus minor) and similar small species in Crete and Malta reveal insular dwarfism, where large animals shrink due to limited resources. These island hippos, along with several species in Madagascar, survived until the Late Pleistocene or early Holocene.
The vast geographic range of the family began to contract significantly due to climate changes, such as the mid-Holocene aridification, which reduced permanent water sources. This environmental stress, combined with increasing human hunting pressure, led to the extinction of all European, Mediterranean island, and Malagasy hippos. Today, the two surviving African species are the last remnants of a once-widespread family.