Hippopotamus

The hippopotamus, often called the common hippo, is a massive semiaquatic mammal. It is native to the sub-Saharan regions of Africa. This animal is a megaherbivore, meaning it is a very large plant-eater. In fact, it is the third largest land mammal on Earth. Only elephants and some rhinoceros species are larger than the hippo. Within its specific group, the even-toed ungulates, it is the largest living member.

To understand how a hippo moves, we must look at its unique anatomy. Their skeletal structure is described as graviportal, which means it is built to support enormous weight. They have very dense bones and a low center of gravity. These features allow them to sink and walk along the bottom of rivers or lakes. Because the water supports much of their mass, they can have relatively short legs. Their toes are webbed to help with movement, and their pelvis sits at a 45-degree angle.

A hippo's body is specially designed for a life shared between land and water. Their eyes, ears, and nostrils are located high on the roof of the skull. This placement allows them to see, hear, and breathe while the rest of their body stays submerged. When they go fully underwater, their nostrils and ears can close tightly. They also have nictitating membranes, which are clear layers that cover and protect their eyes. Even their voices are adapted, as they have horizontal vocal folds similar to those found in baleen whales.

The hippo's mouth is one of its most famous features. Their jaws are powered by massive muscles called the masseter and digastric muscles. The jaw hinge is positioned far back, allowing them to open their mouths at a wide angle of 100 to 110 degrees. This wide gape is possible because of large, droopy cheeks that provide extra muscle attachment space. While they have large canine tusks that can reach 50 centimeters, these are used for combat rather than eating. For food, they use flattened, horny lips to pull up grasses, which are then chewed by their molars.

For a long time, scientists thought hippos were related to pigs because of their teeth. However, modern science has revealed a much different history. By studying DNA and blood proteins, researchers discovered that their closest living relatives are actually cetaceans. This group includes whales, dolphins, and porpoises. The lineage that led to hippos and whales split from other even-toed ungulates about 55 million years ago. This shows how evolutionary paths can diverge in surprising ways.

Evolutionary history shows that hippo ancestors likely entered Africa from Asia. One possible ancestor, the genus *Kenyapotamus*, lived in Africa between 15 and 5 million years ago. The oldest records of the modern *Hippopotamus* genus date back to the Pliocene epoch, roughly 5.3 to 2.6 million years ago. Throughout history, different species have lived in various places. For example, the *Hippopotamus gorgops* was much larger than modern hippos, with a body mass exceeding 3,000 kilograms.

Physical size and weight vary between the sexes and species. An adult male, or bull, typically weighs between 1,500 and 3,000 kilograms. Some exceptionally large males have reached 4,500 kilograms. Females, known as cows, are generally smaller and stop growing around age 25. While bulls continue to grow throughout their lives, cows reach a stable maximum weight.

Finally, we must look at how hippos protect their skin. They have thick, nearly hairless skin that secretes a special substance. This liquid is not actually blood or sweat, even though people sometimes call it "blood sweat." It is a secretion containing two acidic pigments: hipposudoric acid and norhipposudoric acid. These pigments act as a natural sunscreen by absorbing ultraviolet light. They also serve an important biological role by inhibiting the growth of disease-causing bacteria.