The term “tusk” describes an elongated, continuously growing tooth that protrudes from the mouth. While often associated with elephants, the massive front teeth of the hippopotamus fit this description in both function and appearance. These projecting weapons are highly modified incisors and canines. They are central to the hippo’s survival, serving a purpose far removed from simple chewing, and their composition has created a complex conservation issue.
The “Surprising Truth” About Hippo Teeth
Biologically, hippos have dramatically enlarged teeth that function as tusks. The common hippopotamus possesses two pairs of massive, curved lower canines and two pairs of lower incisors, all of which are continuously growing. These lower canines are the most prominent and dangerous of the dental array, with those of a large male capable of reaching lengths of up to 50 centimeters (20 inches).
The material making up these structures is ivory, primarily dentine, the same substance found in elephant tusks. Unlike the elephant’s tusks, which are modified incisors, the hippo’s main weapons are its lower canines. The sheer size and projection of these teeth justify the popular use of the word “tusk,” even though they are technically specialized canines and incisors. These teeth are not used for eating, which is handled by the molars and tough lips, but are reserved for combat.
Form and Function: Why Hippos Need These Teeth
The projecting teeth are primarily weapons of aggression and defense in the hippo’s territorial and social life. They are used in fights between males, known as bulls, who battle to establish dominance over stretches of river and the females within them. These contests involve opening the jaw to 150 to 180 degrees, a wide gape that serves as a visual threat display. If the display fails, the tusks inflict deep, severe wounds on an opponent’s thick hide.
The teeth are also the primary defensive tools used against predators like crocodiles and lions, which typically target young or solitary animals. Ironically, this powerful dental arsenal limits the animal’s ability to chew efficiently. The enormous size and interlocking structure of the front teeth restrict the side-to-side grinding motion that most herbivores use to mulch tough vegetation. This results in a less efficient digestive process, which forces the hippo to spend significant time near water sources where food is easily accessible.
The Biology of Tusk Growth
A defining characteristic of these teeth is their continuous growth throughout the hippo’s lifespan. Both the lower canines and incisors emerge from the jaw and never stop elongating. This constant growth necessitates a mechanism to prevent the teeth from becoming unwieldy or growing back into the animal’s own jaw.
Nature has provided the hippopotamus with a self-sharpening system that keeps the tusks razor-sharp. As the hippo closes its powerful jaws, the lower canines rub and grind against the smaller upper canines. This action wears down the ivory in a way that continuously hones the edges of the lower tusks, much like a pair of scissors. The material itself, hippo ivory, is dense and hard, which historically made it a prized material for carving and even for use in early dental prosthetics.
Hippo Ivory and Conservation Concerns
The composition of hippo teeth as solid ivory has made the species a target in the global wildlife trade. Following international restrictions on elephant ivory, hippo ivory has emerged as a readily available and less regulated substitute in the carving and ornamental markets. This shift has increased the pressure on hippo populations, particularly where poaching is already a threat. Hippo teeth are easier to conceal and smuggle than elephant tusks, making them an attractive commodity for illicit networks.
The common hippopotamus (Hippopotamus amphibius) is currently listed as a Vulnerable species on the IUCN Red List of Threatened Species. This conservation status means that the species does not receive the same high-level international protection afforded to endangered animals. Between 2009 and 2018, an estimated 13,900 hippos were killed for their parts to supply the trade, driven by both poaching and habitat loss. The pygmy hippopotamus (Choeropsis liberiensis) faces even greater peril, as it is classified as Endangered due to its smaller population and restricted range, making the trade in its teeth a profound threat to its survival.