Looking the river Horse in the Mouth: A Reexamination of the Dentitions of the Living Hippopotami

Dentitions of the two living species of hippopotamus, Hippopotamus amphibius and Choeropsis liberiensis were reexamined with regard to tooth numbers and types, and patterns of eruption, occlusion, and replacement. Dental formulae of both species of hippo were found to have been incorrectly interpreted by previous authors. In addition to thegosis, attrition caused by foraging behavior and tongue wear was noted on the incisors. Hippos have ever‐growing incisors and canines, and selection for the presence of unusually large teeth, i. e., tooth and tooth root space, orientation and positional requirements, have shaped the anterior portion of the skull in both species, for foraging and intraspecific competition. A diastema is produced by lateral displacement of the canine and elongation of the anterior rostrum to compensate for elongation of its root in H. amphibius . The latter factor has drastically reduced the available space for the first premolar, resulting in its elimination from the adult dentition, although the deciduous first premolar often persists into adulthood. An increased time interval between successive molar eruptions in the common hippo reflects a possible adaptation to a lifespan of up to sixty years.