Hippo Evolution

On this channel we’ve covered the evolutionary history of some of Earth’s largest creatures, from elephants to rhinos to giraffes. It’s only natural then that we continue this pattern today and take a look at the evolution of the hippopotamus.

There are currently two species of hippos that belong to the family Hippopotamidae: The common hippo, Hippopotamus amphibious and the Pygmy Hippo, Choeropsis liberiensis. They are the last in the lineage that dates back all the way to the Eocene epoch.

It was thought for a while that hippos were most closely related to pigs and peccaries, but it was later found out that these animals had stronger ties to whales and dolphins. These two groups of creatures formed the suborder whippomorpha which branched off from Ruminantia during the early Eocene, around 60 million years ago.

Whippomorpha saw its first major divergence around 5-6 million years later, with one group leading to what are now our modern whales, and the other group splitting off into Anthracotheriidae.

Anthracotheriidae

The anthracotheres were a group of pig-like animals that were prominent during the Eocene epoch. The relationships of these animals among other artiodactyls is still unclear in places, with some more liberal placings grouping it alongside the similarly pig-like entelodonts and the giant Andrewsarchus, with others believing the anthracotheres to be more distant from those ungulate groups. Regardless, it’s generally agreed upon by most scientists to be closely related to whales and hippos and argued by many to be the ancestors of hippopotamuses.

The earliest known member, Elomeryx, was a stout animal from Asia that was roughly 5 feet long in leg. It already showed adaptations for an at least semi-aquatic lifestyle, with incisors suitable for cropping aquatic plant matter. In addition this animal also had wider feet for aid while traversing wetter or muddier terrain, which would make for an ideal lifestyle near bodies of water.

Other members of the group include the two meter long Anthracotherium of Eurasia, which possessed a build not too dissimilar to those of hippos. Anthracotheres became widespread as the Cenozoic possessed, spreading to other continents such as North America and Africa, the latter of which was notable as it was one of the first times large mammals from Eurasia managed to garner a foothold in the continent against its native Afrothere residents.

Unfortunately, the Anthracotheres began to dwindle towards the end of the Miocene, with the early Pliocene genus Merycopotamus being the last known genus of the group. There were several reasons posited for their decline; one such reason deals with the general cooling the Earth faced during this time period and the drying up of the wetter habitats the Anthracotheres were comfortable in. But another reason deals with the fact that they could have been outcompeted by the hippopotamuses that they were supposedly the progenitors of.

The anthracotheres and hippopotamuses shared several morphological and behavioral characteristics that led scientists to link the two groups of animals together. These include the aforementioned aquatic lifestyle, which was believed to have emerged convergently from whales. In addition, the lower jaw of many anthracotheres resembled those of hippos as well.

Hippopotamidae

There are a few animals that are purported to be the first true hippopotamids descended from the anthractoheres, including Morotocheorus from early Miocene Kenya and Uganda. Much of these relationships are drawn upon from similarity in structures present between these animals and more modern hippos but there are still many contentious points regarding whether or not these animals are true members of hippopotamidae or if they’re part of a sister lineage.

The oldest universally agreed hippotamid is the middle Miocene Kenyapotamus, followed shortly after by the later Miocene Archaeopotamus. This particular genus was unique for having an elongated mandibular symphysis, which Wikipedia tells me is the median line between the two bottom halves of the mandible. You can feel it if you touch the middle part of your lower jaw, it’s pretty cool. This structure gave Archaeopotamus’s face a more narrowed look compared to its fellow hippos.

These early hippos would soon be replaced at the end of the Miocene by more modern hippo groups. One such group was the genus Hexaprotodon. This genus bore resemblances to the pygmy hippo, to the point where the pygmy hippo had the same genus name until it was later labeled as its own distinct genus. Hexaprotodon was notable for how far it managed to venture off from the African continent, finding new homes in regions of south Asia, where some species in India managed to cling on until the end of the Pleistocene, around 15,000 years ago.

The last two genera of modern hippopotamuses we’ll discuss are those of the Hippopotamus and Choeropsis genus. The first genus evolved during the tail end of the Pliocene and spawned a number of different forms that ranged from a variety of different sizes and environments.

One of the earliest hippos of this genus was also the largest hippo of all time, Hippopotamus gorgops. At nearly 10,000 pounds in weight, this animal dwarfed even the common hippo of today. It did lead a similarly amphibious lifestyle, and even had greater adaptations for life in water with protruding orbits that allowed its eyes to be placed higher up. This would greatly help it look at the surface when submerged underwater.

In addition, gorgops was also unique for its range. This animal originated in Africa, but migrated all the way into Europe as well.

This genus was notable for possessing numerous dwarf species that inhabited many islands around Africa and the Mediterranean sea. For example there were dwarf hippo species from Cyprus, Crete, and Malta.

What’s more interesting, however, were the Malagasy hippos from Madagascar. While they were nearly identical to modern hippos in their body plans and behavior, they were a fraction of their size due to island dwarfism. Despite their size, the hippos from Madagascar were likely the largest mammals on that island and would find very few threats from predators, with the largest predator on the island, the Fossa likely not having an easy time taking one down. These island hippos such as Lemerle’s Dwarf Hippopotamus and the Malagasy Dwarf Hippopotamus managed to cling on until the Holocene, where they were most likely wiped out by overhunting by humans who migrated to the island.

The only living member of this genus we have today is the Common Hippopotamus of Africa. Very similar to its cousins, this animal has few predators and is in fact one of most dangerous land animals in the world.

Last up is the genus Choeropsis, a much more basal genus that diverged from Hippopotamus around the Miocene. In fact, this genus and animals in it such as the pygmy hippo were more closely related to other extinct hippo genera such as Saotherium than it was to its larger relatives.  On that note, the pygmy hippo, Choeropsis liberiensis is the only living member of its genus today, living in more heavily forested areas compared to the common hippo which inhabits bodies of water near grasslands and savannas.

Conclusion

Both species of hippos today are threatened. The common hippopotamus is listed as threatened whereas the pygmy hippo is listed as endangered. I’ve said this before in my videos about giraffes, elephants, and rhinos, but hippos represent a very unique mammalian form on Earth, and their extinction would be a hard hit on the diversity of life on Earth.

The common hippo is primarily hunted for its meat and because it’s viewed as a dangerous species. While the pygmy hippo is also hunted for food, it also suffers the additional threat of habitat destruction as its forest homes are being destroyed for wood and land.

It’s very easy for me to tell you that in order to preserve these species we can take steps such as making donations to relevant conservation organizations that can assist these creatures out in the wild, as well as buying products that are ethically sourced. But that really is only a fraction of the solution.

This is something I’ve been hesitant to mention in my other videos simply because doing so would end them on a more negative note, but this comment on one of my more recent videos inspired me to bring this matter up. At the end of the day the conservation of many African and Asian species are simply out of our hands. There are a wide variety of reasons why people are driven to hunt these animals, and I’ve only listed a few of them as of now. Poorer individuals feel the need to poach animals for the sake of being able to survive, as their own governments fail to meet their basic needs. Then there’s the internal conflicts such as those in sub saharan Africa which not only affect local people but also the wildlife caught in the crossfire.

Then there’s the greedy and corrupt governments which either refuse to support conservation or indirectly incentivize the killing of vulnerable animal species. When it comes to wanting to preserve a species in the US or Europe such as, say, the Bison, it’s a comparatively easy task. These governments have shown a history of being responsive to environmental issues such as these with acts such as the endangered species act helping animals like Bison, Bald Eagles, and Grizzly Bear from being any more threatened. Even in countries like India there are several acts and laws in place to protect its many endangered animals such as tigers and elephants which have shown evidence of improvement. But I can’t come to you to mince words. At the end of the day, there’s only so much control we have over the fates of animals in countries who we can’t directly influence either because of their global dominance, such as China, or the complicated inner turmoil such as the African or Southeast Asian countries.

He mentions towards the end of his comment that taking steps such as supporting zoos that directly house and deal with the conservation of threatened species is a good way of helping these animals out, and I fully agree. Other than that all we can do is hope and pray for the best. In the meantime, we can also simply appreciate the diversity of life we currently have on Earth.